A 51-year-old woman is admitted to the surgical ward with a 24-hour history of severe abdo… — USMLE Step 2 CK

A 51-year-old woman is admitted to the surgical ward with a 24-hour history of severe abdominal pain, nausea, and obstipation. She has not passed flatus since the symptoms began. Her past medical history is significant for an open appendectomy for perforated appendicitis 15 years ago. The pain was initially intermittent and crampy but transitioned to a continuous, dull ache over the past 4 hours. Temperature is $37.4^\circ\text{C}$ ( $99.3^\circ\text{F}$ ), blood pressure is $138/82\text{ mmHg}$ , pulse is $92/\text{min}$ , and respiratory rate is $16/\text{min}$ . On physical examination, the abdomen is moderately distended and tympanitic. There is focal tenderness to deep palpation in the right lower quadrant, but no rebound tenderness, rigidity, or guarding. Bowel sounds are high-pitched and tinkling. Laboratory studies show a leukocyte count of $10,500/\text{mm}^3$ and a serum lactate level of $1.5\text{ mmol/L}$ (normal: $0.5-2.2\text{ mmol/L}$ ). An intravenous contrast-enhanced CT scan of the abdomen and pelvis reveals a transition point in the distal ileum. Proximal to this point, a distinct, radially distributed, C-shaped cluster of fluid-filled small bowel loops is visualized. The mesenteric vessels supplying this segment demonstrate a converging, twisted configuration. The bowel wall of the involved segment shows normal contrast enhancement, and there is no pneumatosis intestinalis. Which of the following is the most appropriate next step in management?

Immediate exploratory laparotomyAnswer
B
Placement of a nasogastric tube and serial clinical assessments
C
Administration of oral water-soluble contrast medium
D
Intravenous administration of piperacillin-tazobactam and observation
E
Colonoscopic decompression

Answer

Immediate exploratory laparotomy is required due to the presence of a closed-loop obstruction.

The correct answer is immediate exploratory laparotomy. This patient presents with a small bowel obstruction complicated by a closed-loop mechanism. A closed-loop obstruction occurs when a segment of bowel is obstructed at two adjacent points (often by a single adhesive band or a hernia), creating an isolated loop. Radiographic hallmarks include a U-shaped or C-shaped distended fluid-filled loop, and a 'whirl sign' representing the twisting of the mesentery and its vessels. Because the loop is isolated, it cannot be decompressed via vomiting or a nasogastric tube. Fluid secretion rapidly increases intraluminal pressure, leading to impaired venous return, arterial compromise, ischemia, and eventual perforation. Therefore, even when patients are hemodynamically stable and lack overt signs of ischemia (such as normal wall enhancement and a normal lactate level), the anatomical diagnosis of a closed-loop obstruction warrants immediate surgical exploration to prevent bowel infarction.

Step-by-Step Solution

Analyze the patient's history and vital signs.

The patient has signs of a mechanical bowel obstruction (obstipation, vomiting, distension, prior abdominal surgery) but is currently hemodynamically stable without systemic inflammatory response or lactic acidosis.

Initial assessment determines if the patient is in immediate shock or possesses signs of frank bowel necrosis (which would easily mandate surgery).

Evaluate the specific findings on the contrast-enhanced CT scan.

The CT scan shows normal bowel wall enhancement and no pneumatosis, indicating the bowel is not yet necrotic. However, the presence of a C-shaped cluster of loops and a mesenteric 'whirl sign' definitively identifies a closed-loop obstruction.

Differentiating between a simple obstruction and a closed-loop obstruction dictates the entire management pathway.

Synthesize the diagnosis with the standard of care for surgical management.

A closed-loop obstruction isolates a segment of bowel at two points, preventing proximal decompression (e.g., via nasogastric tube). As secretions accumulate, venous pressure rises rapidly, leading to strangulation and infarction even if current labs are normal.

Understanding the pathophysiology of closed-loop obstructions confirms that conservative management is dangerous and immediate surgical exploration is mandatory.

Key Concept

A closed-loop small bowel obstruction (indicated by a C-shaped loop and mesenteric whirl sign on CT) carries an imminent risk of strangulation and is an absolute indication for urgent exploratory laparotomy, even in the absence of peritonitis, leukocytosis, or hemodynamic instability.

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics

More questions from this topic