Imaging in PTAs

Written by: Cameron Jones, MD (NUEM ‘23) Edited by: Vidya Eswaran, MD (NUEM ‘20) Expert Commentary by: Josh Zimmerman, MD

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The Use of Imaging for Diagnosis and Management of Peritonsillar Abscesses

Among the many causes of sore throat that the EM physician may encounter, peritonsillar abscesses (PTAs) can be one of the more satisfying to diagnose and treat. A straightforward clinical diagnosis followed by a simple procedure resulting in a patient who feels much better than when they arrived...right? But what about that patient with the large, short neck and some drooling? Or the one with severe trismus giving you only the barest of glimpses at the back of their throat? Or, most feared of all, the crying child who develops lockjaw at the first glimpse of a tongue depressor? Maybe we should just get the neck CT to be on the safe side? And didn’t I hear about using ultrasound for this in some lecture? 

What is a peritonsillar abscess (PTA)?

A PTA is a discrete collection of pus between the palatine tonsil capsule and the pharyngeal muscles. It should be distinguished from peritonsillar cellulitis, which is an inflammatory reaction of the same area without a definitive collection. PTAs are often preceded by tonsillitis or pharyngitis with subsequent progression of the infection. However, they may also occur due to salivary gland obstruction without preceding tonsillitis or pharyngitis. Peritonsillar abscess is often considered a clinical diagnosis based on classic symptoms and exam findings:

• Throat pain (sometimes worse on the side of the abscess, but not always)

• “Hot potato” or muffled voice

• Unilateral swollen and erythematous tonsil +/- appreciable fluctuance

• Uvula deviation

What are signs or symptoms suggestive of a more dangerous diagnosis?

Though sometimes mistakenly considered features of more concerning deep space neck infections, all of the following can also be seen with PTA: 

• Neck swelling

• Trismus

• Pooling of saliva (though this should be minor, with minimal drooling)

Other findings or symptoms of more serious deep space infections, such as retropharyngeal abscess:

• Toxic appearance

• Respiratory distress

• Anxious appearance or leaning forward into “sniffing position”

• Significant drooling

• Neck pain or limited ROM out of proportion to presumed diagnosis

When should imaging be considered in the patient with suspected PTAs?

Routine imaging is not indicated for stable patients with a presumptive diagnosis based on exam. Sensitivity and specificity figures in the EM and ENT literature based on clinical exam alone are actually not very high (sensitivity <80% and specificity approximately 50%). However, these oft-cited figures are based on a comparatively small cohort of patients with presumed PTA, and in the large majority of missed diagnoses among this data, the true diagnosis is tonsillitis or peritonsillar cellulitis. CT scans, particularly contrast studies and those involving radiation of the head and neck, are not without risk, and should not be considered a screening study in well-appearing patients.  Therefore, the use of imaging by ED physicians in evaluation of PTAs should really be reserved for 3 purposes:

1. Ruling out serious deep space neck infections, such as retropharyngeal abscesses, in a patient with signs of peritonsillar swelling but some other concerning sign or symptom, as discussed above.

   - CT of the neck with contrast is best used for this purpose

2. Differentiating PTA from peritonsillar cellulitis or tonsillitis by identifying a discrete fluid collection

3. Guiding drainage in order to improve first-attempt success

   - Intraoral or submandibular/transcervical ultrasounds are most appropriate for these purposes

 There are few prospective studies examining the use of CT in uncomplicated PTAs, and those patients with red flags or signs of airway compromise are typically excluded. CT of the neck with IV contrast is nearly 100% sensitive and 75% specific for PTA and similarly accurate for the diagnosis of more dangerous conditions such as retropharyngeal abscesses. Increasingly, ultrasound has also become a useful option for better characterizing the location of abscesses in PTAs. 

Ultrasound offers the added utility of bedside confirmation of a drainable fluid collection and, depending on provider comfort and patient tolerance, may provide real-time guidance for needle drainage. As with other applications of ultrasound, the provider must be comfortable with the technique and relevant anatomy. Prospective data indicates EM providers can become comfortable with tonsillar ultrasound technique in as few as 3-4 patients.  In its use in the ED setting, ultrasound has demonstrated nearly 100% sensitivity in differentiating abscess from non-drainable inflammation or cellulitis. Thus, using ultrasound to confirm abscess in those suspected to have PTA may allow patients without drainable fluid collections to avoid unnecessary aspiration attempts.

Peritonsillar abscess seen on submandibular ultrasound. Adapted from Huang et al. 

Arrows indicating edges of the abscess

T : Tonsil

*  :  Submandibular gland

Peritonsillar abscess on CT. Adapted from Kew et al. 

Arrowheads indicating edges of the abscess.

Is imaging useful for guiding drainage of PTAs?

• Ultrasound has also been studied for its utility in guiding drainage and increasing success rate of aspiration attempts. Some studies have reported low patient tolerance or mechanical challenges when using real-time intraoral ultrasound to guide drainage. However, ultrasound has also been shown to improve success-rate of aspiration attempts even when it is used for preceding visualization of the abscess and not for guided drainage.

• More recently, extraoral ultrasound approaches, such as transcervical/ submandibular, have also been studied as an alternative to intraoral techniques, which can be challenging due to mechanical challenges, severe trismus, or patient discomfort. Very limited data suggests submandibular ultrasound may have lower sensitivity compared to intraoral ultrasound when evaluating PTAs, so caution is also warranted when utilizing this technique. 

Intraoral ultrasound approach

(adapted from Secko, Sivitz, et al.)

Submandibular ultrasound approach

(adapted from Secko, Sivitz et al.)

What about imaging in kids?

CT scans are often ordered in pediatric patients, who may have challenging exams due to patient intolerance, and these imaging studies are particularly common in community settings where ENT expertise is not readily available. Clinical accuracy for diagnosing PTA in children appears even lower than in adults, though, as with adults, in most children incorrectly diagnosed with PTAs, the true diagnosis is tonsillitis without a drainable abscess. Many providers would also prefer to avoid the added radiation exposure of CT scans amongst this population. Thus, extraoral ultrasound approaches may be particularly helpful in pediatric patients, many of whom are unlikely to cooperate with intraoral ultrasound. Transcervical ultrasound has also been shown to reduce length of stay, CT radiation exposure, and procedures performed amongst pediatric patients with suspected PTAs, with no change in readmission rates or treatment failures. Although the extraoral ultrasound approach appears to be more technically feasible in children, use of ultrasound may also be more logistically challenging and staffing-dependent. Scans in these studies were performed and read by radiology technicians and radiologists.  

So what is a reasonable approach to incorporating imaging in suspected PTAs?

The growing body of evidence described above has led to several expert recommendations that ultrasound be the first-line imaging for suspected PTAs. While there is variability in different departments regarding the ED provider’s comfort with bedside tonsillar ultrasound or, alternately, the availability of technicians and radiologists for interpreting formal ultrasounds. However, the use of ultrasound  in non-toxic patients with suspected PTA has been shown to be highly effective in differentiating PTAs from peritonsillar cellulitis or tonsillitis and may save patients the discomfort and time of an unnecessary procedure. CT imaging still has its place in those patients with less certain diagnoses or concerning symptoms, but should be reserved for specific scenarios rather than being ordered routinely. The following is an evidence-based algorithm for incorporating ultrasound and CT imaging into the emergency department evaluation of these patients

* : toxic appearance, substantial drooling, respiratory distress, severe neck pain or swelling, inability to fully range neck

+ : Most patients can be safely discharged with oral antibiotics, return precautions, and ENT follow-up. Exceptions include those patients  who are unable to tolerate oral medications, those with signs or symptoms of severe sepsis, patients with severe dehydration, or patient with severe comorbidities or immunocompromised state

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Expert Commentary

Thank you for an excellent review of a common ED diagnosis.  Sore throats are ubiquitous presenting complaints in any major ED.  The final diagnosis is often uncomplicated pharyngitis, however, recognizing the early and often subtle signs of more serious conditions before a true life threat develops is a critical role for the emergency physician.  While peritonsillar abscesses (PTA) in and of themselves are not typically life threatening, many of the signs and symptoms can overlap with those of more critical diagnoses such as retropharyngeal abscesses and epiglottitis.  

So, that said, when should you consider imaging a patient with a suspected PTA or acute sore throat in general?

The discussion above does a thorough review evidenced based imaging practices and offers a reasonable flowsheet to guide this decision.  In clinical practice imaging should help answer one of two questions: 

• Is a discrete fluid collection present that is amenable to drainage? 

• Are there findings of retropharyngeal or other deep space infection rather than a simple PTA?

I have made it my practice to consider imaging before any attempt at I&D or further care in the following circumstances: 

• Any patient toxic in appearance or with unstable vital signs

• Any patient demonstrating signs of airway compromise 

• Meningismus on exam

• Patients in which at PTA cannot be clearly visualized or lacking the typical secondary findings on exam 

With that list in mind, let us delve into the topic a bit more in detail.  Peritonsillar abscesses represent accumulation of purulent fluid which are unlikely to resolve spontaneously.  Some studies have shown that drainage alone results in >90% cure rate even without antimicrobial therapy. Classically, a PTA will present with trismus, severe pharyngitis, and on pharyngeal exam a displaced tonsil, typically inferiorly and medially, as well as uvular deviation contralateral to the abscess.  PTA can sometimes be confused with peritonsillar cellulitis on examination solely and is often one of the reasons clinicians opt for imaging. Peritonsillar cellulitis does not require drainage as there is no discrete fluid collection.  When there is a more subtle exam, this is one scenario in which imaging may be helpful.   

A practical approach that many ED physicians utilize is to consider a trial of drainage when the diagnosis is readily evident on exam.  As mentioned above, when the classic findings of a displaced tonsil and uvula are present one can have a high probability of successful drainage.  

Adjunct therapy – abx and steroids 

The scope of this segment is meant to focus on imaging and diagnostics but it is worth a brief moment to discuss antimicrobials and adjunct therapy.  While procedural drainage alone results in significant cure rates, it remains common practice to treat PTA’s with antimicrobial therapy as well.  A common misconception is that PTAs are a result of Streptococcal infections.  While Group A Strep is isolated from cultures, these typically tend to be polymicrobic infections with Fusobacterium additionally being a frequent culprit organism.  As such, antibiotic therapy tends to be more broad spectrum with coverage of anaerobic organisms included.  First line therapy remains a penicillin based antibiotic regimen.  Intravenously this can be ampicillin-sulbactam (Unasyn), Piperacillin-Tazobactam (Zosyn) or Ceftriaxone Plus Metronidazole.  In the penicillin allergic patient Clindamycin is a reasonable alternative.  When transitioning to oral therapies, Amoxicillin-Clavulanate (Augmentin) is typically first line therapy with Clindamycin providing a reasonable alternative in penicillin allergic patients.  Therapy typically is for a full 10 days.  

A brief note should be made regarding steroid therapy as well.  Steroids have been shown to provide significant symptomatic relief including decreasing length of symptoms and overall severity.  I typically will give patients a single dose or oral or IV Dexamethasone 10 mg as part of their treatment. 

Joshua Zimmerman, MD

Emergency Medicine Physician

Northwestern Lake Forest Hospital

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How To Cite This Post:

[Peer-Reviewed, Web Publication] Jones, C. Eswaran, V. (2021, Jan 11). Imaging in PTAs. [NUEM Blog. Expert Commentary by Zimmerman, J]. Retrieved from http://www.nuemblog.com/blog/imaging-in-PTAs.

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References

1. Carratola, M. C., Frisenda, G., Gastanaduy, M., & Lindhe Guarisco, J. (2019). Association of Computed Tomography With Treatment and Timing of Care in Adult Patients With Peritonsillar Abscess. Ochsner Journal, 19, 309–313. https://doi.org/10.31486/toj.18.0168

2. Costantino, T. G., Satz, W. A., Dehnkamp, W., & Goett, H. (2012). Randomized Trial Comparing Intraoral Ultrasound to Landmark-based Needle Aspiration in Patients with Suspected Peritonsillar Abscess. Academic Emergency Medicine, 19(6), 626–631. https://doi.org/10.1111/j.1553-2712.2012.01380.x

3. Cunha, B., Filho, A., Sakae, F. A., Sennes, L. U., Imamura, R., & De Menezes, M. R. (n.d.). Intraoral and transcutaneous cervical ultrasound in the differential diagnosis of peritonsillar cellulitis and abscesses Summary. Brazilian Journal of Otorhinolaryngology, 72(3), 377-81. http://www.rborl.org.br/

4. Fordham, M. T., Rock, A. N., Bandarkar, A., Preciado, D., Levy, M., Cohen, J., … Reilly, B. K. (2015). Transcervical ultrasonography in the diagnosis of pediatric peritonsillar abscess. The Laryngoscope, 125(12), 2799–2804. https://doi-org/10.1002/lary.25354

5. Froehlich, M. H., Huang, Z., & Reilly, B. K. (2017, April 1). Utilization of ultrasound for diagnostic evaluation and management of peritonsillar abscesses. Current Opinion in Otolaryngology and Head and Neck Surgery. Lippincott Williams and Wilkins. https://doi.org/10.1097/MOO.0000000000000338

6. Herzon, F. S., & Martin, A. D. (2006). Medical and Surgical Treatment of Peritonsillar, Retropharyngeal, and Parapharyngeal Abscesses. Current Infectious Disease Reports, 8:196–202. https://doi.org/10.1007/s11908-006-0059-8

7. Huang, Z., Vintzileos, W., Gordish-Dressman, H., Bandarkar, A., & Reilly, B. K. (2017). Pediatric peritonsillar abscess: Outcomes and cost savings from using transcervical ultrasound. The Laryngoscope, 127(8), 1924–1929. https://doi.org/10.1002/lary.26470

8. J Scott, P. M., Loftus, W. K., Kew, J., Ahum, A., Yue, V., & Van Hasselt, C. A. (2020). Diagnosis of peritonsillar infections: a prospective study of ultrasound, computerized tomography and clinical diagnosis. The Journal of Laryngology and Otology, 113, 229–232. https://doi.org/10.1017/S0022215100143634

9. Kew, J., Ahuja, A., Loftus, W. K., Scott, P. M. J., & Metreweli, C. (1998). Peritonsillar Abscess Appearance on Intra-oral Ultrasonography. Clinical Radiology (Vol. 53).

10. Lyon, M., & Blaivas, M. (2005). Intraoral Ultrasound in the Diagnosis and Treatment of Suspected Peritonsillar Abscess in the Emergency Department. Academic Emergency Medicine, 12(1), 85–88. https://doi.org/10.1111/j.1553-2712.2005.tb01485.x

11. Nogan, S., Jandali, D., Cipolla, M., & DeSilva, B. (2015). The use of ultrasound imaging in evaluation of peritonsillar infections. The Laryngoscope, 125(11), 2604–2607. https://doi.org/10.1002/lary.25313

12. Patel, K. S., Ahmad, S., O’leary, G., & Michel, M. (1992). The role of computed tomography in the management of peritonsillar abscess. Otolaryngology--Head and Neck Surgery, 107(6), 727-732.  https://doi.org/10.1177/019459988910700603.1 

13. Powell, J., & Wilson, J. A. (2012). An evidence-based review of peritonsillar abscess. Clinical Otolaryngology, 37(2), 136–145. http://doi.wiley.com/10.1111/j.1749-4486.2012.02452.x

14. Salihoglu, M., Eroglu, M., Osman Yildirim, A., Cakmak, A., Hardal, U., & Kara, K. (2013). Transoral ultrasonography in the diagnosis and treatment of peritonsillar abscess. https://doi.org/10.1016/j.clinimag.2012.09.023

15. Valdez, T. and Vallejo, J., 2016. Infectious Diseases In Pediatric Otolaryngology. Springer International Publishing.

Non Contrast CT Head for the EM Physician

Written by: Philip Jackson, MD (NUEM ‘20) Edited by: Logan Weygandt, MD, MPH NUEM ‘17) Expert Commentary by: Katie Colton, MD

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Relying on in-house radiology reads of imaging is a habit that EM trainees are encouraged to avoid, but one that can be appealing when practicing in a busy, large academic facility with 24-hour radiologist staffing. By reading one’s own images, not only do EM physicians gain skills in diagnostic radiology, which they can employ when an attending radiology read is not readily available but more importantly, the EM physician can correlate history and physical with imaging and help detect subtle pathology. Recent studies have shown that even attending EM physicians are often deficient in reading non-contrast CT scans of the head, however, with minimal training residents have been shown to make significant improvements. [2,3]

An elderly male with a history of hypertension and Fuch’s corneal dystrophy presented to our ED the morning after developing acute on chronic worsening of the blurry vision in his R eye. He suffered from persistent blurry vision but stated that it had suddenly worsened while watching TV the previous night. He then developed a left-sided occipital headache that continued through the following morning. He also noticed that his thinking was “cloudy” and despite being a healthcare professional could not describe his own medical history or list of medications. He described blurriness especially on the right. On visual field confrontation, the patient was found to have a binocular R sided superior quadrantanopsia. The rest of his neurologic exam was unremarkable. As these findings were concerning for stroke specifically in the left temporooccipital region known as Myer’s loop, we obtained a STAT non-contrast head CT.

As the so-called green arrow-signs on the CT image indicate, there was indeed a significant amount of cerebral edema present in the L temporal lobe white matter, which  contains the anterior optic radiations carrying information from the R superior visual field and corresponds to our patient’s deficit. Upon discovering this lesion, our team immediately called our radiology colleagues who confirmed our concern for an acute ischemic infarct.

Like any other task in the ED, reading a head CT should be conducted as efficiently and accurately as possible using a standardized approach. EM residents have been found to be somewhat deficient in our ability to evaluate noncontrast head CTs; however, studies have shown that with adequate training, our skills can significantly improve. [3] Perron et al describe the simple but systematic approach “Blood Can Be Very Bad.” This mnemonic reminds residents to examine for the presence Blood, the shape and consistency of the Cisterns, the texture of the Brain parenchyma, the Ventricles, and the presence of fractures and symmetry of the Bony structures. 

• Blood:  In a non-contrast CT, blood will appear as hyperdense (bright/white) fluid.  As blood ages over weeks, it will become increasingly hypodense (darker).  Blood will present in one of the four following ways:

  • Subarachnoid hemorrhage - A dreaded complication of trauma, a ruptured aneurysm, or an arteriovenous malformation can lead to blood pooling in gravity-dependent areas correlating with the particular arterial defect. Rupture of the anterior communicating artery (ACA) will distribute blood in and around the interhemispheric fissure, suprasellar cistern, and brainstem.  Rupture of the middle cerebral artery (MCA) will distribute blood in the Sylvian and suprasellar cistern, while the posterior cerebral artery (PCA) will also distribute in the suprasellar cistern.

  • Subdural hemorrhage (SDH) – Caused by rupture of the bridging veins, SDHs will present as a crescentic lesions that often cross suture lines. SDHs can be acute, chronic, or mixed, and thus will have varying degrees of density.

  • Epidural Hemorrhage - Another serious complication of trauma, epidural hemorrhages will present as a lenticular (biconvex) areas of hyper-attenuation.     Caused by arterial laceration, with the most common being the middle meningeal artery, epidural hemorrhages can rapidly expand and cause significant and rapid mass effect.  Early identification is thus crucial to reducing mortality from these injuries.

  • Intraparenchymal/intraventricular hemorrhage - Often the result of hypertensive disease in elderly patients or as hemorrhagic strokes, intraparenchymal hemorrhage will most often be located in the basal ganglia. Amyloid angiopathy  (associated with Alzheimer’s dementia) often presents as wedge-shaped areas of hemorrhage in the outer cortex. Trauma leading to brain contusion can also present with intraparenchymal hemorrhage. All intraparenchymal hemorrhages (as well as subarachnoid hemorrhages) can potentially rupture into ventricles causing intraventricular hemorrhage and resultant hydrocephalus.

• Cisterns:  Cisterns are spaces surrounding and cushioning brain matter with cerebrospinal fluid. Each of the four major cisterns should be examined for blood or signs of mass effect: the sylvan fissure (in between temporal and parietal lobes), the circummesencephalic or peripontine cistern, the suprasellar (surrounding the circle of Willis), and the quadrigeminal (atop the midbrain).

• Brain matter: Always examine the gyri for and for distinct grey-white matter differentiation. Ischemic strokes, as in our case, will present with blurring of the grey-white differentiation and cerebral edema (areas of hypodensity).  Early strokes may not be apparent on CT, but after 6 or more hours hypodense lesions should be present with maximal edema occurring approximately 3-5 days after the event. Always examine the falx for midline shift through multiple slices.

• Ventricles:  Examining the third and fourth ventricles is crucial in determining the presence of blood hydrocephalus (dilation) or mass effect (asymmetry).

• Bone:  The bony structures of the head should all be examined for fractures, especially depressed skull fractures, which usually denote intracranial pathology. Also, examining the sphenoid, maxillary, ethmoid, and frontal sinuses for air fluid levels should raise suspicion for a skull fracture. Separate bony windows are available for close examination of these high-density structures. [1]

As our case illustrates, it is crucially important for EM physicians to interpret non-contrast CT scans in a systematic and accurate manner. Clinical correlation is a distinct advantage that we, as emergency physicians, possess and it should be exploited to allow for timely and effective patient care.

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Expert Commentary

Thanks to Drs. Jackson and Weygandt for this great primer to the emergent head CT.  One of the obvious challenges of EM is the breadth of pathology we see, and so having a strategic approach like this one will reveal most of the emergent diagnoses we are looking for.  I will never be a radiologist, but nothing is faster than looking at my own scan. A few thoughts: I start by scrolling a scan through quickly to identify obvious pathology (a bleed, midline shift, etc.) and then try to actively redirect my attention back to a systematic approach. It is easy to hone in on the obvious abnormality and miss smaller but crucial clues. Go through the same progression every time. Get comfortable with finding different windows for your imaging. If you only look in a brain window, you’ll miss critical diagnoses. Symmetry is your best friend - until it is not.  We are remarkably good at picking out asymmetry when looking at imaging, which reveals many of the emergent diagnoses, but keep some of the symmetric processes in the back of your mind.  Many of these can wait for a radiologist’s fine- tooth comb, but a few stand out.  Get used to finding the basilar artery, particularly in your unconscious patient; an acute occlusion in this midline structure is potentially devastating but quick intervention is life-saving. Similarly, acute hydrocephalus merits immediate intervention that can lead to dramatic clinical improvement. Bilateral or midline subdural hemorrhage can also be easily missed; finding these requires a level of comfort with windowing the images and identifying abnormal CSF spaces.

Katie Colton, MD

Instructor, Feinberg School of Medicine

Department of Neuro Critical Care and Department of Emergency Medicine

Northwestern Memorial Hospital

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How To Cite This Post:

[Peer-Reviewed, Web Publication] Philip, J. Weygandt, L. (2020, Feb 10). Non Contrast CT Head for the EM Physician. [NUEM Blog. Expert Commentary by Colton, K]. Retrieved from http://www.nuemblog.com/blog/non-contrast-ct-head-for-the-em-physician

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References

1. Adams, James, and Erik D. Barton. Emergency Medicine: Clinical Essentials. 2nd ed. N.p.: Elsevier Health Sciences, 2013;633-644.

2. Jamal K, Mandel L, Jamal L, Gilani S. 'Out of hours' adult CT head interpretation by senior emergency department staff following an intensive teaching session: a prospective blinded pilot study of 405 patients. Emergency medicine journal : EMJ. 2014;31(6):467-470.

3. Perron AD, Huff JS, Ullrich CG, Heafner MD, Kline JA. A multicenter study to improve emergency medicine residents' recognition of intracranial emergencies on computed tomography. Annals of emergency medicine. 1998;32(5):554-562.

4. Mayfield Brain & Spine. "Visual field test." Visual Field Test | Mayfield Brain & Spine. N.p., n.d. Web. 19 Dec. 2016.

Contrast Allergies for the Emergency Medicine Physician

Written by: Niki Patel, MD (NUEM ‘22) Edited by: Jesus Trevino (NUEM ‘19) Expert Commentary by: Seth Trueger, MD, MPH

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Expert Commentary

Thank you for this nice review. The main points I try to keep in mind is that contrast reactions are rare; they are rarely severe; and if a patient did not have a prior severe reaction (especially with pretreatment), it is very unlikely that they will have a severe reaction. Pretreatment probably does little but there are only so many hills to die on and most radiology departments won’t let us completely forego pretreatment. The key is working politely with the radiologists & techs to advocate for the patient and what they need (and if that means a consent form or removing a spurious allergy from the EHR, sure).

In my experience, institutional guideline are generally taken directly from the ACR guidelines (which is the point of specialty guidelines!) and therefore means ED patients need, at most, 4 hour prep; and anyone who hasn’t had a serious airway or anaphylactic reaction can probably be safely scanned with pretreatment as the potential benefit of the scan is higher than the potential risk of a reaction. Any scan that can wait for an 8 or 13 hour prep can be ordered by the admitting team (although I will get the pretreatment ball rolling to help them out). Occasionally a patient needs a scan so urgently they can get immediate doses of steroids and antihistamines and scanned immediately, and with proper SDM & documented consent, we can usually make this happen.

For preps, I try to document all the timing as clearly as possible because shifts change (docs, RNs, radiology techs, etc) and will usually put it clearly in the note & trackboard:

• 0730 methylpred 40mg IV

• 1030 diphenhydramine 50mg IV

• 1130 methylpred 40mg IV + CTPE

In my experience, communicating clearly with everyone involved as to what the plan is is the best way to ensure the plan gets carried out.

And lastly, there is no relation between seafood allergies and contrast allergies; you can’t be allergic to “iodine” (although that is fine as shorthand in the EHR to document a reaction); and there is no cross-allergy between topical povidine-iodine irritation and iodinated contrast (don’t ask).

Seth Trueger, MD, MPH

Assistant Professor of Emergency Medicine

Department of Emergency Medicine

Northwestern University expert commentator

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How To Cite This Post:

[Peer-Reviewed, Web Publication] Patel, N. Trevino, J. (2020, Aug 10). Contrast Allergies for the Emergency Medicine Physician. [NUEM Blog. Expert Commentary by Treuger, S]. Retrieved from http://www.nuemblog.com/blog/contrast-allergies-for-the-em-physician.

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A Practical Approach to Abdominal Imaging

Written by: Zach Schmitz MD (PGY-3) Edited by: David Kaltman, MD (PGY-4) Expert commentary by: Samir Abboud, MD

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I often find myself in a gray zone when it comes to imaging abdominal pain. Any third year medical student worth their salt can tell you to get the RUQ ultrasound for the fat, fertile, forty year-old female with RUQ abdominal pain, fever, positive Murphy’s sign, and leukocytosis. However, my patients don’t usually fit the textbook, and I’m often thinking about what I might miss or see with test X vs test Y. Below, I’ll touch on a few common dilemmas where the optimal choice of imaging modality isn’t immediately clear by focusing on what you actually gain or lose by ordering one imaging test over another.

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Scenario 1: Stone or Appendicitis?

Case: 62 year old female with HTN and HLD presents with RLQ pain. The pain woke her this morning and has been intermittent all day, occurring exclusively when she urinates. It is sharp, non-radiating, and increasing in intensity. She never had a pain like this and can now barely sit still. She has thrown up a few times over the past few hours. Vitals are stable and she is afebrile. She appears uncomfortable with RLQ tenderness but no rebound or guarding. Labs show slight leukocytosis, and urine has no blood.

If I suspect stone over appendicitis, will a CT without contrast miss appendicitis?

• CT, MR, and US are well studied in their ability to detect and accurately diagnose appendicitis.[1] 

  • CT with IV contrast is 96-100% sensitive and 91-100% specific. Per the American College of Radiology’s (ACR) appropriateness system, this is the most appropriate initial test for suspected appendicitis in adults.[2]

  • MR is 96% sensitive and 96% specific.[3]

  • Ultrasound has a wide range of data, with sensitivity ranging from 21-95.7% and specificity of 71-97%.[2]

• CT without oral or IV contrast is nearly as useful for diagnosing appendicitis

  • A meta-analysis by Xiong et al included seven original studies investigating a total of 845 patients.[4]

    • Pooled sensitivity - 0.90 (95% CI: 0.86-0.92)

    • Pooled specificity - 0.94 (95% CI: 0.92-0.97)

    • Pooled positive likelihood ratio - 12.90 (95% CI: 4.80-34.67)

    • Pooled negative likelihood ratio - 0.09 (95% CI: 0.04-0.20)

Will a contrast enhanced CT for appendicitis ruin my chance to catch a kidney stone?

• Non-contrast CT is the emergency standard in diagnosing nephrolithiasis with good reason - it is 97% sensitive and 95% specific.[5]

• Will contrast ruin the ability to detect a stone?

  • This makes theoretical sense as stones and contrast are both hyper-intense on CT.

  • Sensitivity is decreased for small stones with contrast enhanced studies.

  • However, for stones > 3mm, sensitivity remains 95%.[5]

  • Only about 5% of stones that small ultimately require intervention.

Takeaways: You sacrifice a bit with a non-contrast study looking for appendicitis and a contrast enhanced study looking for stone, but both still work well. The American Urology Association recommends consultation for stones > 10mm.[6] Urology would also need to be involved with signs of sepsis, abscess, deterioration in renal function, intractable symptoms, or a transplant/solitary kidney. It seems I am very likely to see a stone requiring something other than watchful waiting on a CT with contrast. It is worse to miss an appendicitis than a 2mm stone, so contrast might make more sense if it’s close. 

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Scenario 2: RUQ Ultrasound after Negative CT San

Case: 84 year old male with a history of prostate cancer and hypertension presents from a nursing home with 4 days of diffuse abdominal pain. He has had no vomiting or bowel movements over this time. No urinary symptoms. He is hemodynamically stable, and his abdomen is diffusely tender (maybe worse in the RUQ) and distended but overall not terribly impressive. You order a CT for possible obstruction and it just shows a large stool burden. The gallbladder was visualized and looked normal. 

If a CT is negative, should I get a RUQ US to look for cholecystitis?

• RUQ Ultrasound

  • Per ACR, this is the most appropriate initial study for RUQ pain and suspected biliary disease.[7]

  • A 2012 meta analysis showed a sensitivity of 81% (95% CI 75-87%) and specificity of 88% for acute cholecystitis.[8]

  • It has the advantage of being dynamic, with a sonographic Murphy sign independently showing an 86% sensitivity and 35% specificity, positive predictive value of 43%, and negative predictive value of 82%.[9] 

• Computed Tomography (CT) 

  • The same 2012 meta analysis only had one study with CT, but noted a sensitivity of 94% with fairly broad confidence intervals (95% CI 73-99) and a specificity of only 59%.[8]

  • ACR notes CT’s NPV for acute cholecystitis approaches 90%.[7]

  • A 2015 study looked at 101 patients who went to the OR and got both a CT and US. For acute cholecystitis, the sensitivities for CT and US were 92% and 79% respectively. For cholilithiasis, sensitivities for CT and US were 60% and 89% respectively.[10,11]

  • ACR states it is “usually appropriate” to proceed with CT for RUQ pain and suspected biliary disease with a negative or equivocal ultrasound.[7]

  • Although it lacks a sonographic murphy’s sign equivalent, its advantage is to help in operative planning and seeing complications, such as perforation or gangrene.

• MRI has a sensitivity of 85% and a specificity of 81%. It is also considered “usually appropriate” by ACR if ultrasound is negative or equivocal[7]

• Cholescintigraphy is the best imaging, showing 97% sensitivity and 90% specificity for acute cholecystitis. It is also the most appropriate study if you suspect acalculous cholecystitis.[7]

Takeaways: There are a few interesting points from this set of data. First, CT seems to have at least as good of ability to pick up cholecystitis compared to ultrasound. However, it is much worse in detecting gallstones themselves, which may be very relevant to a patient with abdominal pain. Second, the sensitivity of both RUQUS or CT isn’t really that great and we are probably missing a few episodes of cholecystitis. If there is a very high index of suspicion but negative imaging, it may be worthwhile to pursue additional workup. Overall, if the CT shows a normal gallbladder, and you are not worried about intractable biliary colic, the ultrasound probably won’t add much. 

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Scenario 3: Female Pelvic Pain

Case: 33 year old female with a history of chlamydia infection presenting with right sided abdominal pain. The pain has gradually been getting worse for 1 day. She has had a few episodes of vomiting. There is some white vaginal discharge she always has. On exam, she is tachycardic, normotensive, and febrile to 101.5. She has RLQ tenderness with voluntary guarding. On pelvic exam, there is some white vaginal discharge, CMT, R adnexal tenderness that seems less intense than her RLQ tenderness, and no masses noted.

If this patient had a normal appendix and ovaries after a contrast enhanced CT for appendicitis, how useful is an additional transvaginal ultrasound to rule out gynecologic pathologies?

For ovarian torsion:

• A retrospective study of 834 patients showed the NPV of a contrast enhanced CT of the pelvis for ovarian torsion is 100%.[12]

• A prospective study of 199 patients showed doppler ultrasound has a sensitivity and specificity for torsion of 100 and 97%.[13]

For Tubo-Ovarian Abscess (TOA):

• CT is thought to be between 78 and 100% sensitive.[14]

• 2011 literature review gives a broad range of sensitivity and specificity for US in TOA with a sensitivity of 56-93% and specificity from 89-98%.[15]

Takeaways: ACR appropriates rates ultrasound as the most appropriate test for female pelvic pain.[14] However, it also rates CT with contrast as more appropriate for suspected appendicitis.[2] This patient raises concerns for both, and a CT was done first. CT is good for finding intra abdominal and pelvic abscess. It is more difficult to assess how useful ultrasound is for TOA, as many studies in the literature review were either before year 2000 or used a transabdominal approach. Overall, if someone has a CT scan for appendicitis that shows normal ovaries, the transvaginal ultrasound seems to add little for either torsion or TOA.

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One potential dangerous conclusion from this set of data is that we should just CT everyone up front. While CT shows good sensitivities for many of the pathologies in question, simply ordering a CT first ignores the many good reasons - such as cost, radiation dose, speed, improved specificity and comparable sensitivity, resource utilization, sonographic murphy sign - RUQUS and pelvic ultrasound are the most appropriate initial tests for suspect biliary and pelvic pathology. That said, it a patient has an entirely normal CT that was already performed for other indicated reasons, the use of additional imaging may be unnecessary and should be considered carefully. Overall, the question of exactly what imaging test to order when ruling out common, emergent, abdominal pathologies is often a difficult one with shades of gray. By having a better understanding of exactly what type of information we are getting and missing from each test we order, emergency physicians can more quickly, safely, and accurately diagnose and treat our patients.

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Expert Commentary

This is a thoughtful, well-reasoned approach to optimizing the imaging strategy in challenging, atypical clinical scenarios. To add a few nuances to some of the points raised:

When considering a contrast-enhanced versus non-contrast CT (both IV and PO) in the clinically ambiguous scenario, it is important to consider your patient’s body habitus. Figure 1 includes representative images from a non-contrast enhanced CT of a patient with a BMI above 25. You can clearly see the inflammatory stranding in the right lower quadrant mesenteric fat (Figure 1a) and portions of an appendicolith (Figure 1 b), in this patient who ultimately proved to have appendicitis. The natural contrast provided by the patient’s mesenteric fat in this scenario helps us work around the absence of IV contrast.

Figure 1a

Figure 1b

Figure 2 includes representative images from a contrast enhanced CT of a very thin patient, with a relative paucity of intra-abdominal fat. In this patient, the relative absence of natural contrast would greatly reduce our chances to diagnose appendicitis (or even identify the appendix) in the absence of IV contrast. PO contrast is additionally likely to be most helpful in very thin patients [Alabousi 2015].

Figure 2

The author asks (and answers) a very insightful question with regards to identifying kidney stones on contrast enhanced CT. A few points to add:

Assuming the contrast enhanced study is obtained prior to the excretory phase of imaging (and most routine studies are) ureteral stones should still be largely visible - the stones that will generally be more difficult to identify will be the non-obstructing stones still within the collecting system. Additionally, while there is indeed a small sacrifice in sensitivity for small stones with contrast enhanced studies, the identification of secondary complications is much improved.

Consider Figure 3, which demonstrates a 2 mm stone in the proximal left ureter identified on a contrast enhanced study. Notice the slightly delayed nephrogram on the left relative to the right, which could indicate a component of obstructive uropathy. Similarly, identification of such complications as pyonephrosis, pyelonephritis, and perinephric abscess is much improved with contrast enhanced images. For this reason, I would suggest that in the clinically ambiguous scenario, erring on the side of the contrast enhanced study would be wise.

Figure 3

It is important to note that the CT scanner installed in our emergency department is a dual-energy machine. Many of our other departmental scanners are dual-energy as well. With these scanners, we are able to apply algorithms to deconstruct the elemental composition of stones and provide more information than simply size and location - i.e. uric acid or non-uric acid stone - if requested. We can additionally generate virtual non-contrast images from the contrast-enhanced images, without exposing our patients to additional radiation. While it is tempting to think that we could recapture some of the sensitivity for renal stones using these virtual non-contrast images, this has unfortunately not been borne out in the literature at this time [Vrtiska 2010], though remains an area of continued investigation as imaging technology is further improved.

The advantages of dual-energy imaging are not only limited to the kidneys. With regards to the evaluation of biliary colic, virtual monochromatic images can be generated with resulting increased conspicuity of gallstones, even those that appear isodense to bile on the conventional images [Ratanaprasatporn 2018].

In general, if you find yourself with a high degree of suspicion for any disease process and discordant imaging findings, I would encourage you to call your radiologist. The additional clinical information exchanged during such a call may direct what additional data sets should be generated and what additional imaging studies may be of most benefit. Last, but certainly not least, that “second look” armed with additional clinical information can pick up on subtle findings that are, in isolation, entirely non-specific, but in a certain clinical scenario could clinch the diagnosis you are seeking.

References:

Alabousi A et al. Is Oral Contrast Necessary for Multidetector Computed Tomography Imaging of Patients With Acute Abdominal Pain? Canadian Association of Radiologists Journal. 2015;66(4): 318 - 322

Ratanaprasatporn L et al. Multimodality Imaging, including Dual-Energy CT, in the Evaluation of Gallbladder Disease. Radiographics 2018;38(1): 75-89

Vrtiska TJ et al. Genitourinary Applications of Dual-Energy CT. American Journal of Roentgenology. 2010;194: 1434-1442.

Samir Abboud, MD

Assistant Professor of Radiology

Northwestern University

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How To Cite This Post:

[Peer-Reviewed, Web Publication] Schmitz, Z. Kaltman, D. (2020, Feb 10). An Approach to Abdominal Imaging. [NUEM Blog. Expert Commentary by Abboud, S]. Retrieved from http://www.nuemblog.com/blog/abdominal-imaging.

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References

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2. American College of Radiology. ACR Appropriateness Criteria®: RLQ pain. Available at https://acsearch.acr.org/docs/69357/Narrative/ Accessed 5/10/19.

3. Duke E, Kalb B, Arif-Tiwari H, et al. A Systematic Review and Meta-Analysis of Diagnostic Performance of MRI for Evaluation of Acute Appendicitis. AJR Am J Roentgenol 2016;206:508-17.

4. Xiong B, Zhong B, Li Z, Zhou F, Hu R, Feng Z, Xu S, Chen F. Diagnostic Accuracy of Noncontrast CT in Detecting Acute Appendicitis: A Meta-analysis of Prospective Studies. Am Surg. 2015 Jun;81(6):626-9.

5. Curhan G, Aronson M, Preminger G. Diagnosis and acute management of suspected nephrolithiasis in adults. UpToDate.com. April 30 2019. 

6. Assimos D, Krambek A, Miller N et al. Surgical Management of Stones: AUA/Endourology Society Guideline (2016). https://www.auanet.org/guidelines/kidney-stones-surgical-management-guideline. Accessed 5/10/19.

7. American College of Radiology. ACR Appropriateness Criteria®: RUQ pain. Available at https://acsearch.acr.org/docs/69474/Narrative/ .

8. Kiewiet J.J., Leeuwenburgh M.M., Bipat S., et al: A systematic review and meta-analysis of diagnostic performance of imaging in acute cholecystitis. Radiology 2012; 264: pp. 708-720.

9. Bree, Robert L. Further observations on the usefulness of the sonographic Murphy sign in the evaluation of suspected acute cholecystitis. Journal of Clinical Ultrasound. March/April 1995.

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12. Lam A1, Nayyar M2, Helmy M2, Houshyar R2, Marfori W2, Lall C2.Assessing the clinical utility of color Doppler ultrasound for ovarian torsion in the setting of a negative contrast-enhanced CT scan of the abdomen and pelvis. Abdom Imaging. 2015 Oct;40(8):3206-13. Doi: 10.1007/s00261-015-0535-4.

13. Laufer, M. Ovarian and fallopian tube torsion. UpToDate. April 30 2019. https://www.uptodate.com/contents/ovarian-and-fallopian-tube-torsion?search=ovarian%20torsion&source=search_result&selectedTitle=1~70&usage_type=default&display_rank=1 .

14. Beigi, R. Epidemiology, clinical manifestations, and diagnosis of tubo-ovarian abscess. UpToDate. April 30 2019. https://www.uptodate.com/contents/epidemiology-clinical-manifestations-and-diagnosis-of-tubo-ovarian-abscess?search=tuboovarian%20abscess&source=search_result&selectedTitle=2~24&usage_type=default&display_rank=2 .

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16. American College of Radiology. ACR Appropriateness Criteria®: Female Pelvic Pain. Available at https://acsearch.acr.org/docs/69503/Narrative/ .