Hirschsprung disease is diagnosed definitively through a rectal biopsy that checks for missing nerve cells in the bowel wall. This biopsy has a sensitivity between 93.7% and 100% and a specificity up to 100%, making it one of the most reliable diagnostic tests in pediatric surgery. But reaching that biopsy typically involves a stepwise process: recognizing early warning signs, performing imaging, and sometimes doing a pressure test on the rectum before confirming with tissue analysis.
Early Signs That Raise Suspicion
The first clue often appears in the newborn period. Healthy full-term newborns typically pass their first stool (meconium) within 48 hours of birth. A delay beyond that window raises concern for Hirschsprung disease, though only about 50% of affected infants actually show this delay. The other half pass meconium on time, which means a normal first stool does not rule the condition out.
Beyond the newborn period, the hallmark symptoms are chronic constipation, a visibly swollen belly, and poor feeding or slow weight gain. Infants may vomit green bile. In older children, the presentation can look a lot like ordinary constipation, which is one reason the diagnosis is sometimes delayed by months or even years. A key distinguishing feature: children with Hirschsprung disease rarely soil their underwear, because the problem is a segment of bowel that cannot relax, not a behavioral or dietary issue.
What Happens During the Physical Exam
A doctor examining a child with suspected Hirschsprung disease will look for abdominal distension and signs of malnutrition. The most telling part of the exam is a digital rectal examination. In a characteristic finding sometimes called the “squirt sign,” the examiner inserts a gloved finger into the rectum and finds it empty. When the finger is withdrawn, a sudden gush of stool and gas follows. This happens because the finger temporarily opens the narrowed, non-functioning segment and allows trapped contents to escape. While not present in every case, this finding is highly suggestive and usually triggers further testing.
Contrast Enema Imaging
The first formal diagnostic step is usually a contrast enema, an X-ray study where a radiologist introduces contrast dye into the rectum and takes images of the large intestine. The hallmark finding is a transition zone: a funnel-shaped area where the bowel abruptly changes from a narrow, non-functioning segment to a dilated, backed-up segment above it. This transition zone sits at the boundary between the bowel that lacks nerve cells and the bowel that has them.
In one study of 27 confirmed patients, the transition zone was visible on contrast enema in 67% of cases. Of those, 78% showed the transition at the rectosigmoid junction (where the rectum meets the sigmoid colon), which is the most common location for the disease. Plain abdominal X-rays can also hint at the diagnosis. Researchers found that a simple upright abdominal film showed a tapering of the colon gas shadow with an abrupt cutoff in 89% of patients, sometimes making it a useful screening tool before a full contrast study.
Contrast enema is helpful but not perfect. It can miss the transition zone in very young newborns (whose colon hasn’t had time to dilate above the affected segment) and in cases where the entire colon is involved. Radiologists also look at the ratio of the rectum’s width to the sigmoid colon’s width. Normally the rectum is wider; when it’s narrower than the sigmoid, that reversal supports the diagnosis.
Anorectal Manometry
This pressure-based test measures how the muscles of the rectum and anus respond to stretching. A small balloon is inflated inside the rectum while sensors measure the pressure in the internal anal sphincter (the ring of muscle that keeps the anus closed at rest). In a healthy person, inflating the balloon triggers a reflexive relaxation of that sphincter, a response called the rectoanal inhibitory reflex. The reflex is considered present when sphincter pressure drops by at least 25%.
In Hirschsprung disease, this reflex is completely absent. The nerve cells that coordinate the relaxation response are missing, so the sphincter stays tight regardless of how full the rectum becomes. This is the same mechanism that causes the chronic obstruction: the affected bowel segment cannot relax to let stool pass through.
Anorectal manometry is useful as a screening tool, especially in older children where the clinical picture overlaps with functional constipation. A normal reflex essentially rules out Hirschsprung disease. An absent reflex, however, still needs to be confirmed with a biopsy.
Rectal Biopsy: The Definitive Test
The gold standard for diagnosing Hirschsprung disease is a rectal biopsy. The most common method is a suction rectal biopsy, which can be done at the bedside or in an outpatient setting without general anesthesia. A small instrument is inserted into the rectum and uses gentle suction to collect a tiny sample of the bowel wall, including the deeper layer (submucosa) where the nerve cells normally reside.
Pathologists then examine the tissue under a microscope looking for two things: the absence of ganglion cells (the nerve cells that control bowel movement) and the presence of abnormally thickened nerve bundles. In a study of 216 biopsy specimens, 83.8% of Hirschsprung cases were identified by these two features. Pathologists typically examine an average of 10 tissue sections before concluding that ganglion cells are truly absent, because missing them on a few slices doesn’t necessarily mean they aren’t there.
Systematic reviews put the overall sensitivity of suction rectal biopsy at about 96.8% with a specificity of 99.4%. These numbers mean false negatives are rare but possible, and false positives are almost unheard of. When initial results are uncertain, the tissue is re-examined by a second experienced pathologist before additional specialized staining techniques are used.
Special Staining Techniques
Standard tissue staining identifies the presence or absence of ganglion cells in most cases, but borderline samples sometimes need additional analysis. For decades, a stain that highlights a specific enzyme in nerve fibers was considered the go-to supplement. However, this technique requires fresh (unfrozen) tissue, is technically demanding to perform, and shows significant disagreement between pathologists interpreting the results.
A newer staining method using a protein called calretinin has largely replaced the older approach in many centers. Calretinin staining works on preserved, paraffin-embedded tissue (the standard way biopsies are processed), making it far more practical. The interpretation is also straightforward: nerve fibers in the submucosa either stain positive (normal bowel, Hirschsprung unlikely) or negative (no ganglion cells, consistent with Hirschsprung disease). Studies report sensitivity of 93.3% to 100% and specificity of 93.8% to 100%, with significantly less disagreement between pathologists compared to the older method.
Conditions That Can Mimic Hirschsprung Disease
Several other conditions cause similar symptoms, particularly in newborns. Meconium plug syndrome and meconium ileus both cause failure to pass stool in the first days of life. Low imperforate anus (a structural abnormality) and distal intestinal atresia (a blockage) can also look identical in the earliest days. These are usually distinguished through imaging and physical examination before a biopsy is needed.
In older children, the main diagnostic challenge is separating Hirschsprung disease from functional constipation, which is far more common. Contrast enema usually distinguishes the two. A rarer and more difficult group of conditions involves other motility disorders where the nerve cells are present but abnormal. These include intestinal neuronal dysplasia, hypoganglionosis (too few ganglion cells rather than none), and internal sphincter achalasia. Because these conditions can produce similar symptoms and overlapping imaging findings, the rectal biopsy is essential for telling them apart.
The Role of Genetic Testing
Hirschsprung disease has a strong genetic component, particularly involving mutations in the RET gene. In families with a known history of the disease, RET mutations appear in up to 50% of cases. Among children with no family history (sporadic cases), 15% to 35% still carry a RET mutation. Genetic testing is not used to make the initial diagnosis, since the biopsy is faster and more definitive. But it becomes relevant for family planning and genetic counseling, especially when one child in a family has already been diagnosed, as it helps estimate the risk for future siblings.