What is the admitting impression for a patient presenting with a change in bowel pattern, decreased stool caliber, and alternating constipation and diarrhea?

Admitting Impression: Partial Bowel Obstruction vs. Fecal Impaction

The most likely admitting impression for this patient is partial bowel obstruction secondary to fecal impaction, particularly if the patient has risk factors such as immobility, advanced age, or institutionalization. 1, 2

Primary Differential Diagnosis

Fecal Impaction (Most Likely)

• Alternating constipation and liquid stool is pathognomonic for fecal impaction or partial bowel obstruction 1
• Immobility dramatically slows gastrointestinal motility and is the primary risk factor for fecal impaction in bedridden patients 2
• Digital rectal examination can immediately identify fecal impaction in 80% of cases and is both diagnostic and potentially therapeutic 2
• Elderly, institutionalized patients under psychotropic medications causing chronic constipation are classic presentations 1

Partial Small Bowel Obstruction (Secondary Consideration)

• Adhesions account for 55-75% of intestinal obstructions, followed by hernias (15-25%) and malignant tumors (5-10%) 3
• CT abdomen/pelvis is the gold standard with approximately 90% accuracy for identifying the level and cause of obstruction 3, 2
• The transition point on CT appears as focal area where bowel caliber abruptly changes from dilated (>3 cm) proximally to collapsed distally 3

Sigmoid Volvulus (Less Likely but Critical to Exclude)

• Classic presentation includes abdominal pain, constipation, and vomiting (late sign) 1
• 30-41% of patients report previous episodes of abdominal distention 1
• Plain abdominal radiographs showing classic "coffee bean sign" projecting toward upper abdomen are diagnostic 1
• More common in elderly institutionalized patients but presents more acutely than fecal impaction 2

Critical Clinical Assessment Points

History Elements That Matter

• Previous abdominal surgery significantly increases likelihood of adhesive small bowel obstruction 4
• Chronic constipation history points toward fecal impaction, especially with immobility 2, 5
• Duration of symptoms: several days suggests fecal impaction or low-grade obstruction; acute onset suggests volvulus 1
• Neuropsychiatric issues may make history unreliable, requiring greater reliance on physical examination 1

Physical Examination Findings

• Abnormal bowel sounds and abdominal distention are the best physical examination predictors of bowel obstruction 4
• Empty rectum on digital examination is classic for sigmoid volvulus 1
• Absence of peritonitis does NOT exclude bowel ischemia 1
• Asymmetric gaseous abdominal distention with emptiness of left iliac fossa is pathognomonic for sigmoid volvulus, though challenging to detect 1

Laboratory Red Flags

• Elevated white blood cell count, elevated lactic acid, or elevated serum amylase raise suspicion for ischemic complications 1
• Blood gas and lactate levels are crucial, although bowel ischemia may be present without hyperlactatemia 1
• Electrolytes and renal function testing necessary due to dehydration risk in elderly patients with comorbidities 1

Diagnostic Imaging Algorithm

Initial Imaging

1. Plain abdominal radiographs first to look for coffee bean sign (sigmoid volvulus) or obvious obstruction 1

   • However, plain radiographs have limited value with only 50-60% sensitivity and may delay definitive diagnosis 2

2. CT abdomen/pelvis with IV contrast is the definitive study 1, 3

   • Diagnostic accuracy >90% for distinguishing obstructive from non-obstructive ileus 1, 3
   • No oral contrast required in suspected high-grade obstruction as nonopacified fluid provides adequate intrinsic contrast 1
   • Oral contrast may delay diagnosis and increase aspiration risk 3

CT Findings to Report

• Transition point location where dilated bowel meets collapsed bowel 3
• Signs of ischemia: abnormally decreased or increased bowel wall enhancement, intramural hyperdensity, bowel wall thickening, mesenteric edema, ascites, pneumatosis, or mesenteric venous gas 1
• High-risk features: closed-loop obstruction, volvulus, mesenteric edema, free intraperitoneal fluid, "feces sign" in small intestine 3

Important Pitfall to Avoid

Do NOT attribute decreased stool caliber alone to colorectal cancer. 6

• "Pencil thin stool" is a lay misconception from the 19th century with no reliable data support 6
• Low caliber stool occurs with any loose stool or diarrheal state, which are much more common than colorectal cancer 6
• In absence of red flag symptoms (rectal bleeding, weight loss, anemia, positive occult blood), decreased stool caliber alone does not warrant cancer workup 7, 6

Admission Justification

Admit for:

• Bowel rest with NPO status 1
• IV fluid resuscitation for dehydration and electrolyte correction 1
• Nasogastric tube decompression if evidence of high-grade obstruction 1
• Serial abdominal examinations to monitor for peritonitis or clinical deterioration 1
• Surgical consultation if CT shows ischemia, closed-loop obstruction, volvulus, or complete obstruction requiring urgent intervention 1, 3