Hirschsprung disease (HD) is usually diagnosed early in childhood, but can rarely manifest in later childhood (age > 10 years old) or adulthood. Complications of HD include bowel obstruction, bowel necrosis, bacterial overgrowth and infection from stool stasis. Our case highlights the need for a high index of suspicion for HD in patients with chronic constipation without a clear medical etiology, in order to avoid long term complications. A 42-year-old man with a past medical history of chronic constipation presented with abdominal pain, nausea, vomiting, and diarrhea for 4 days. He had similar episodes in the past requiring intravenous fluids during Emergency Department visits. On physical examination, the patient had hypoactive bowel sounds, abdominal distention, and stool in rectum. Computed tomography of the abdomen/pelvis revealed severe constipation and dilated rectosigmoid colon measuring 19 cm. The patient was placed on an extensive bowel regimen with moderate stool clearance. He refused elective colon resection or biopsy. Follow-up imaging showed decreased stool content. He was discharged home on Miralax twice a day and Linzess daily, with adequate bowel movements. Outpatient colonoscopy demonstrated erythematous rectal mucosa with a hyperplastic polyp. Outpatient anorectal manometry showed normal resting and squeeze pressures and an absent rectal sensation and recto-anal inhibitory reflex suggestive of HD. The patient eventually became amenable to a rectal biopsy that revealed aganglionic neural bundles on S100 immunostatin stain consistent with a diagnosis of HD In 75% of cases, the rectosigmoid is the affected colonic segment and in 10% there is total aganglionosis of the colon. Usually, symptoms present within the first year of life and account for 80% of cases; late diagnosis is often consistent with ultra-short segment hirschsprung disease (USHD), which lacks increased acetylcholinesterase in the mucosal layers when compared to HD. Anorectal manometry is a reliable tool to aid in the diagnosis of HD with specificity and positive predictive value of 97% and 95 % respectively when combined with rectal biopsy. There is controversy surrounding the diagnostic criteria for USHD. Some believe the criteria should be modified to include ≤4 cm of aganglionosis; this would help define proper biopsy technique and decrease recurrence from insufficient resection. This area of contention warrants further study.Figure: CT A/P (8/2/16) Severe constipation with massive dilatation of the rectosigmoid colon with the sigmoid colon measuring up to 19 cm in diameter with moderate wall thickening of the rectosigmoid colon which may represent a stercoral colitis.Figure: Anorectal manometry showing normal squeeze pressures.Figure: Anorectal manometry showing normal resting pressures.