During morning rounds, a 64-year-old woman is evaluated for a newly elevated temperature. … — USMLE Step 2 CK

During morning rounds, a $64$ -year-old woman is evaluated for a newly elevated temperature. She is currently on her sixth postoperative day following a low anterior resection with a primary colorectal anastomosis for rectal adenocarcinoma. Her postoperative course was initially uncomplicated, and a transurethral bladder catheter was removed $3$ days ago. Over the past $24$ hours, the patient has developed suprapubic pressure, frequent voiding of small urine volumes, and three episodes of loose, watery stool.

Her temperature is $38.7^\circ\text{C}$ ( $101.7^\circ\text{F}$ ), blood pressure is $122/78$ mmHg, pulse is $110$ /min, and respirations are $18$ /min. Physical examination reveals a dry and intact midline laparotomy incision with no surrounding erythema or fluctuance. Palpation of the lower abdomen elicits moderate deep tenderness, but there is no involuntary guarding or rebound tenderness.

Laboratory results are as follows:
Leukocyte count: $16,500/\text{mm}^3$
Urinalysis:
Color: Yellow
Appearance: Cloudy
Specific gravity: $1.015$
Leukocyte esterase: Positive
Nitrites: Negative
WBCs: $30$ - $40$ /hpf
Bacteria: None

Which of the following is the most appropriate next step in the management of this patient?

Computed tomography of the abdomen and pelvisAnswer
B
Initiation of empiric oral fluoroquinolone therapy
C
Bedside opening of the skin and subcutaneous tissues
D
Insertion of a nasogastric tube for gastric decompression
E
Immediate transfer to the operating room for exploratory laparotomy

Answer

Computed tomography of the abdomen and pelvis

The correct answer is a CT scan of the abdomen and pelvis. This patient's presentation of fever, lower abdominal tenderness, diarrhea, and sterile pyuria on postoperative day 6 following a low anterior resection is highly suspicious for a pelvic abscess. An anastomotic leak leading to a contained fluid collection in the pelvis can directly irritate the adjacent rectum (causing diarrhea) and the urinary bladder (causing sympathetic cystitis, characterized by urgency, frequency, and leukocytes in the urine without bacteriuria or nitrites). In a hemodynamically stable patient, a CT scan with contrast is the diagnostic modality of choice to confirm the presence of an abscess, evaluate the integrity of the anastomosis, and potentially guide percutaneous drainage.

Step-by-Step Solution

Analyze the patient's timeline and vital signs.

The patient is on postoperative day (POD) 6 with a new high fever and tachycardia.

Establishing the postoperative timeline is crucial for narrowing the differential diagnosis of a fever (e.g., abscesses typically present around POD 5-7).

Evaluate the localizing symptoms and laboratory data.

The patient exhibits suprapubic pressure, sterile pyuria (WBCs present but negative for bacteria and nitrites), and recent onset of diarrhea.

These findings point to inflammation adjacent to the bladder and rectum, rather than isolated pathology within the urinary tract or intestinal lumen.

Synthesize the findings with the patient's specific surgical history.

The patient underwent a low anterior resection, a procedure with a notably high risk for anastomotic leak and subsequent pelvic abscess formation.

A pelvic fluid collection resting in the Pouch of Douglas can directly irritate the adjacent bladder wall (causing 'sympathetic cystitis') and rectum (causing diarrhea).

Determine the appropriate diagnostic test for the suspected condition.

A CT scan of the abdomen and pelvis is required.

Imaging is the definitive study to identify and localize an intra-abdominal or pelvic abscess in a hemodynamically stable patient, guiding potential percutaneous drainage.

Key Concept

Pelvic abscesses following colorectal surgery typically present 5-7 days postoperatively and can cause 'sympathetic cystitis' (sterile pyuria, urgency, frequency) and diarrhea due to contiguous inflammation of the adjacent bladder and rectum. The next best step for diagnosis in a hemodynamically stable patient is a CT scan of the abdomen and pelvis.

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