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:
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
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
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