Tag Archives: Abscess

Student Corner: CT Evaluation of Appendicitis

April 9, 2015


Appendicitis is commonly encountered in the ER and is the leading cause of surgical emergency in the abdomen. The initial evaluation for a presentation that is concerning for appendicitis often includes history taking and exam, supplemented by labs. The Alvarado Score is a 10 point rating scale that is widely used as a tool to help decide whether or not a patient presenting with abdominal pain requires CT imaging (although it’s overall clinical usefulness is controversial). It is outlined here by MDCalc. According to the rule, a score of greater than 4 warrants CT evaluation and greater than 7 requires immediate surgical consult.  CT scan is a highly sensitive and specific tool in diagnosing appendicitis, however it comes with radiation, cost, and sometimes IV contrast risks.  In the pediatric patient population radiation from CT scans are not as desirable as the long-term consequences have theoretical potential to be deleterious (long discussion…for another post maybe!).

The purpose of this article is to go over characteristics of appendicitis that can be seen on a CT scan. The use of contrast is a long debated point of contention amongst the emergency medicine community and the usual practice varies between institutions. Medscape has a great rundown of the issue here, which notes that the use of contrast may be more beneficial in circumstances where appendicitis is a relatively less likely diagnosis because the contrast better helps characterize other possibilities.  Contrast studies are also more helpful in the patient not expected to have a large amount of intraperitoneal fat.

As usual, it is important to understand the local anatomy when analyzing radiological images of the abdomen. The image below is an example of an axial cut, non-contrast abdominal CT of a patient who came in with abdominal pain concerning for appendicitis. Try to identify the following structures: vertebrae, psoas major, IVC, iliac arteries, small bowel, colon and appendix.


And below is a labeled version of the same image:

Appendicitis labeled

Key: Blue arrow = bowel gas, ascending colon; Green arrows = small bowel; Purple arrows = L and R Iliac arteries; Yellow arrow = IVC; Red arrow = inflamed appendix

This image contains several signs that indicate that the appendix is inflamed. They include:

  • Diameter greater than 6mm–this usually implies the the appendix has either been twisted or blocked off from the cecum by an appendicolith, which causes inflammation
  • Periappendiceal fat stranding–seen as distinct lines that radiate out from the appendix in the image above, it is caused by inflammation of the appendix causes fluid accumulation around the wall of the appendix which turns the normally hypodense surrounding fat into a hyperdense area; note that the visceral fat around the appendix on the L side of the image looks much different than the visceral fat on the other side of the image
  • Appendiceal wall thickening–normally the wall of the appendix is thin and barely noticeable, but this image shows that the wall is generally thickened and may even be slightly more hyperdense than expected (more below)

Other signs that aid in the diagnosis of appendicitis include:

  • Appendiceal wall enhancement–the wall of the appendix becomes slightly more hyperdense when you compare it to the wall of any other loop of bowel, which is again a product of inflammation; note that this finding is usually more evident on contrast-enhanced CT
  • Abscess–the colon has a large reservoir of commensal bacteria, which can grow and wall off into an abscess if they are trapped in the appendix
  • Appendicolith–a calcified mass that is hyperdense on CT which can be an obstruction between the cecum and the appendix

Overall, CT has a high degree of sensitivity and specificity when used to evaluate the possibility of appendicitis. The clues outlined above, especially when seen together and as a part of a larger clinical picture that fits with appendicitis, are instrumental in confirming the diagnosis.


Ohle R, O’Reilly F, O’Brien KK, Fahey T, Dimitrov BD. The Alvarado score for predicting acute appendicitis: a systematic review.BMC Med. 2011 Dec 28;9:139. doi: 10.1186/1741-7015-9-139. Review. PubMed PMID: 22204638; PubMed Central PMCID: PMC3299622.

Reich B, Zalut T, Weiner SG. An international evaluation of ultrasound vs. computed tomography in the diagnosis of appendicitis.Int J Emerg Med. 2011 Oct 29;4:68. doi: 10.1186/1865-1380-4-68. PubMed PMID: 22035447; PubMed Central PMCID: PMC3215954.

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Liver mass…differential diagnosis

July 14, 2014


This patient presented with right upper quadrant pain.  I asked last week what your differential diagnosis would be:

Liver Mass 1

Liver mass 2

The CT above shows a multiloculated, rim-enhancing mass in the liver parenchyma.  This is consistent with an abscess.  The differential diagnosis starts by breaking down the categories into bacterial, fungal, and amebic causes. 

Bacterial:  Abscesses can form from ascending cholangitis, especially in setting of biliary malignancies.   Klebsiella pneumoniae has been reported to cause hepatic abscesses, especially in E. Asia (1).  Patients with recent instrumentation (hepatocellular carcinoma embolization, etc) are at risk for MRSA, streptococcus species.  Tuberculosis has been known to cause hepatic abscesses as well.

Fungal:  Disseminated candidiasis in the immunocompromised host can lead to liver and splenic abscesses

Amebic:   Liver abscess is the most common manifestation of extraintestinal entamoeba histolytica (2).  In endemic areas or travelers to endemic areas are at risk for this occurrance. 

Author:  Russell Jones, MD


1.  Davis J, McDonald M.  Pyogenic Liver Abscesses.  www.uptodate.com

2.  Leder K, Weller P.  Extraintestinal Entamoeba Histolytica Amebiasis.  www.uptodate.com


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Liver mass…

July 7, 2014


This patient presented with right upper quadrant pain…

Liver Mass 1

Liver mass 2

The CT above shows a multiloculated, rim-enhancing mass in the liver parenchyma.  What is your differential diagnosis?

Author:  Russell Jones, MD

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Necrotizing Fasciitis

January 17, 2013

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I saw a patient the other day with a gluteal/perianal swelling consistent with abscess.  It looked erythematous, swollen, tender and indurated as a usual abscess would be…roughly 10cm extending from the external anal sphincter into the gluteal area.  What made this abscess interesting was that we could feel a small amount of crepitus on exam.  Bedside ultrasound was hindered by what appeared to be air (unfortunately I didn’t save the ultrasound!).  Here is what appeared on CT imaging of her pelvis:

Nec Fasc 1

This is a non-contrast CT because the patient’s creatinine was elevated.  However you can see extensive gas formation in the gluteal area.  It extended up near the sacrum and rectum.  The patient was taken to the operating room for debridement with concerns for necritizing fasciitis.  The amount of gas on CT was not anticipated based on physical exam (the patient had only a little bit of crepitus that could have been missed).

Necrotizing fasciitis on imaging shows up as air in the soft tissue.  This can be seen on plain films but the extent is better characterized on CT.

A couple learning points from this case:

1.  Use ultrasound on your abscesses!  You never know what you may find.

2.  Crepitus is bad.  Even a little bit.  Consider a deep, serious infection that could spread rapidly.

3.  If Necritizing Fasciitis is suspected:  obtain early broad spectrum antibiotics, resuscitation, surgical consultation, and CT imaging for characterization.

Author:  Russell Jones, MD

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Left Lower Quadrant Pain

December 15, 2012

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Here is an interesting CT abdomen in a middle-aged patient with 10 days of left lower quadrant pain and fevers:

This patient has an 8cm abscess from perforated diverticulitis.

In the center of the image you can see a large air and fluid filled cavity with surrounding fat stranding.  This is consistent with an intraperitoneal abscess.  In middle-aged and elderly patients diverticulitis is a very common cause of intraabdominal abscess.  Other causes include perforated appendicitis, post-surgical infection, inflammatory bowel disease, surgical site anastomotic leak, perforated peptic ulcer, gangrenous cholecystitis, mesenteric ischemia with perforation, and pancreatic abscess.

Abscesses on CT have several classic features:

1.  Heterogeneous contents including various densities of fluid and debris with gas formation

2.  Rim enhancement with IV contrast due to high blood flow to the structure

3.  Surrounding inflammation seen as fat stranding

Radiology usually likes oral contrast if you suspect an intraabominal abscess because it helps distinguish abscess cavities from surrounding loops of bowel.  If you are studying abscesses in soft tissues or organs such as the liver, oral contrast is unnecessary.

Author:  Russell Jones, MD

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Why can’t you inject Heroin into your gluteus musculature?

October 1, 2012


Because it can easily end up in abscesses:

Notice the two rim-enhancing lesions with center hypoattenuation consistent with abscesses on both gluteal areas.  He also has stranding surrounding the area of concern.  This CT image is near the distal sacrum of the pelvis.

He admitted to injecting “tar heroin” intramuscularly in his bilateral gluteal areas.  Last injection was over three days ago and he had a fever, leukocytosis.  With the stranding, rim enhancement, and the clinical picture these were considered abscesses rather than simple fluid of the injected heroin.  This patient would be at risk for MRSA (Methicillin-resistant Staph. Aureus) and was covered with IV clindamycin and admitted to the surgical service for further evaluation and possible operating room intervention.

Author:  Russell Jones, M.D.

Imaging Study:  CT Pelvis with IV Contrast

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