During morning rounds, the surgical team examines a 41-year-old male patient who underwent… — USMLE Step 2 CK

During morning rounds, the surgical team examines a 41-year-old male patient who underwent an emergency appendectomy for a perforated appendix six days ago. Over the last 24 hours, he has developed lower abdominal discomfort, tenesmus, and the passage of several small-volume, loose stools. His temperature is $38.9^\circ\text{C}$ ( $102^\circ\text{F}$ ), blood pressure is 118/76 mmHg, pulse is 105/min, and respirations are 18/min. Cardiopulmonary examination is unremarkable. The midline abdominal incision is clean, dry, and intact with no surrounding erythema, fluctuance, or induration. Deep palpation of the lower abdomen elicits moderate tenderness, but no rebound or guarding is appreciated. Digital rectal examination reveals a markedly tender, boggy mass positioned anteriorly. Laboratory studies show a leukocyte count of $18,500/\text{mm}^3$ . Which of the following is the most appropriate next step in the management of this patient?

Computed tomography scan of the abdomen and pelvisAnswer
B
Stool assay for Clostridioides difficile toxins
C
Opening of the abdominal incision at the bedside
D
Immediate empiric administration of intravenous vancomycin and piperacillin-tazobactam
E
Immediate return to the operating room for exploratory laparotomy

Answer

Computed tomography scan of the abdomen and pelvis

This patient is presenting with classic signs of a postoperative pelvic abscess, a recognized complication following surgery for a ruptured intra-abdominal organ such as a perforated appendix. These deep space infections typically manifest between postoperative days 5 and 7 with fever, leukocytosis, and localized abdominal pain. Because fluid preferentially tracks down into the dependent portion of the peritoneal cavity (the recto-vesical pouch in men), a localized abscess often irritates the adjacent rectum. This rectal irritation produces symptoms of tenesmus and frequent, small-volume diarrhea, which can easily be misdiagnosed as gastroenteritis or antibiotic-associated colitis. The key physical examination finding is a tender, fluctuant, or boggy mass palpable on a digital rectal examination. The most appropriate next step is to obtain a computed tomography (CT) scan of the abdomen and pelvis. This imaging modality will confirm the diagnosis, characterize the size and location of the fluid collection, and determine if the abscess is amenable to less invasive percutaneous CT-guided or ultrasound-guided drainage, which is the standard of care over open surgical re-exploration.

Step-by-Step Solution

Analyze the postoperative timeline and vital signs.

The patient is on postoperative day 6 following a contaminated surgery (perforated appendix) and has developed a new fever and tachycardia.

Timing of postoperative fever helps narrow the differential diagnosis; POD 5-7 strongly correlates with deep surgical site infections or intra-abdominal abscesses.

Evaluate the localized symptoms and physical examination findings.

The patient exhibits tenesmus, small-volume diarrhea, lower abdominal tenderness, and a tender, boggy mass anterior to the rectum on digital rectal exam.

These findings localize the pathology. The boggy mass in the recto-vesical pouch (or pouch of Douglas in females) is the hallmark physical exam finding of a pelvic abscess.

Determine the diagnostic modality of choice.

A CT scan of the abdomen and pelvis is selected.

Imaging is required to definitively diagnose the presence, size, and loculation of the abscess to guide subsequent management, such as percutaneous image-guided drainage.

Key Concept

Pelvic Abscess Presentation and Management

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