What are the signs and physical findings of fecal impaction?

Signs of Fecal Impaction

Fecal impaction presents with a large mass of dry, hard stool in the rectum or proximal colon confirmed by digital rectal examination, though paradoxical watery diarrhea from overflow is the most commonly misinterpreted sign. 1, 2

Clinical Presentation

Gastrointestinal Symptoms

• Paradoxical overflow diarrhea is the hallmark sign where watery stool from higher in the bowel leaks around the impaction, mimicking diarrhea despite underlying severe constipation 1, 2
• Absence of passage of flatus (90% of cases) and/or feces (80.6% of cases) 1
• Abdominal distension and bloating (65.3% of cases) 1
• Colic-like abdominal pain, particularly in the left lower quadrant 1
• Recurrent abdominal pain with gradual symptom development 1
• Vomiting (less frequent than in small bowel obstruction) 1

Physical Examination Findings

Digital rectal examination is the diagnostic gold standard for distal impaction, revealing a large mass of hard, compacted stool in the rectum 1, 3. However, a critical pitfall is that proximal impactions in the sigmoid colon will have a non-diagnostic DRE, requiring imaging for confirmation 1, 3.

Abdominal Examination

• Tenderness on palpation 1
• Abdominal distension 1
• Hyperactive bowel sounds (early) or absent bowel sounds (late/severe cases) 1
• Possible palpable fecal mass through the abdominal wall 4

Rectal/Perineal Examination

• Hard stool mass palpable on digital rectal examination (distal impaction) 1, 3
• Empty rectum on DRE suggests proximal impaction requiring imaging 1, 3
• Possible rectal bleeding from stercoral ulceration 1, 5

Atypical Presentations in High-Risk Populations

Elderly debilitated patients may present with life-threatening circulatory, cardiac, or respiratory symptoms rather than gastrointestinal complaints 6. This atypical presentation is particularly dangerous as the diagnosis may be missed.

Systemic Signs

• Fever, tachypnea, tachycardia, and confusion (if perforation has occurred) 1
• Signs of dehydration: orthostatic hypotension, tachycardia, dry mucous membranes, poor skin turgor 2
• Urinary retention or overflow incontinence from mass effect on the bladder 5
• Fecal incontinence from paradoxical overflow 5

Laboratory Findings

• Electrolyte imbalances, particularly elevated urea nitrogen and metabolic alkalosis from vomiting and dehydration 1
• Leukocytosis and neutrophilia (suggests perforation or necrosis) 1
• Elevated amylase levels and lactic acidosis (ominous signs suggesting perforation) 1

Diagnostic Confirmation

Imaging Studies (When DRE is Non-Diagnostic)

• Plain abdominal X-ray can image the extent of fecal loading and exclude bowel obstruction, though it has limited sensitivity 1
• CT scan is the diagnostic test of choice for confirming large bowel obstruction, identifying proximal impaction location, and detecting complications 1, 2
• Abdominal ultrasound performs better than plain X-ray but worse than CT 1

Critical Pitfalls to Avoid

• Never assume a negative DRE rules out fecal impaction—proximal sigmoid impactions require imaging for diagnosis 1, 3
• Don't treat the "diarrhea" with antidiarrheals—the watery stool is overflow from impaction, and treating it will worsen the underlying problem 2
• Don't miss atypical presentations in the elderly—cardiopulmonary symptoms may be the only manifestation 6
• Be vigilant for life-threatening complications: colonic perforation, stercoral ulceration, urinary tract obstruction, renal insufficiency, and severe electrolyte imbalances 5