Pathophysiology of Hypoganglionosis

Hypoganglionosis associated with chronic stool retention, similar to that seen in Hirschsprung disease (HD), is rare, accounting for only 5% of all classified congenital innervation defects of the colon (1). In 1964, Bentley first described five cases of hypoganglionosis in 22 cases of megasigmoid and megarectum (2). However, the understanding of hypoganglionosis is controversial because diagnostic criteria are not strictly defined internationally. A consensus conference recommended that three to five full-thickness biopsies of the intestinal wall should be used to demonstrate the features characteristic of hypoganglionosis: very low overall level of acetylcholinesterase (AchE) activity in the intestinal mucosa, significant deficiency of nerve cells in myenteric plexuses, and hypertrophy of the muscularis mucosa and muscle layers (3). The aim of this study was to make a comparison between three cases of hypoganglionosis we have studied and those cases previously reported in the literature to document the clinical and histochemical features of hypoganglionosis, to make recommendations for its management, and to describe its prognosis. During the past 13 years, three cases of hypoganglionosis (all boys) were identified by examining full-thickness biopsy specimens taken during surgery of the proximal and distal jejunum; the proximal, middle, and distal ileum; the colon; and the rectum. Hematoxylin and eosin (H&E) staining and assessment of AchE activity visualized by the method described by Karnosvsky and Roots were used (4). These patients died of severe enterocolitis at 4, 4, and 7 months of age. At autopsy, the enteric nervous system of the entire gut (esophagus to rectum) was examined. Each segment was cut into 0.5×0.5-cm specimens and either snap frozen for AchE histochemistry or embedded in paraffin for H&E staining. Specifically, we investigated the location of disease and histologic abnormalities and attempted to correlate them with symptoms and prognosis. We compared our cases with cases previously reported in the English literature. A search of the English-language literature using the key word “hypoganglionosis” was performed and previous reports reviewed. CASE REPORT In our cases, on H&E staining, ganglion cells were observed in submucosal and myenteric plexuses, from the esophagus to the colon and rectum. Two patients had hypoganglionosis extending from the upper jejunum to the rectum, and one had hypoganglionosis extending from the esophagus to the rectum. Preoperative rectal-suction biopsy specimens from all three patients showed absence of AchE-positive nerve fibers and presence of ganglion cells in the submucosa. In full-thickness specimens taken during surgery, no proliferation of AchE-positive nerve fibers in the mucosa was identified, although some AchE-positive nerve fibers were noted in the circular and longitudinal muscle layers throughout the gut (Fig. 1). All specimens from affected bowel had normal submucosal plexuses, and hypoganglionotic myenteric plexuses (Fig. 2). Ganglion cells that were present were mature (Fig. 3). No nerve trunks were identified in specimens from any of our patients.FIG. 1.: Acetylcholinesterase (AchE) histochemistry. No proliferation of AchE-positive nerve fibers in the mucosa is identified, although a moderate number of AchE-positive nerve fibers can be seen in the circular and longitudinal muscle layers in the ascending colon in this specimen from a patient with hypoganglionosis (×200). Cm, circular muscle layer; lm, longitudinal muscle layer; ms, mucosal layer ganglion cell (arrow).FIG. 2.: Acetylcholinesterase histochemistry. Normal submucous and hypoganglionotic myenteric plexuses from the ileum of a patient with hypoganglionosis (×200). Cm, circular muscle layer; lm, longitudinal muscle layer; ms, mucosal layer.FIG. 3.: Hematoxylin–eosin staining. Ganglion cells (arrowhead) in submucous plexuses were mature in the ileum from a patient with hypoganglionosis (×400). Cm, circular muscle layer; lm, longitudinal muscle layer).DISCUSSION In the literature, all previous reports have described hypoganglionosis of myenteric plexuses (5–9), but only three reports have described submucosal plexuses (10–12). Munakata et al. (12) reported six cases of hypoganglionosis of myenteric plexuses associated with small ganglia in submucosal plexuses. In four of these, the diseased segment was short and involved only the rectum. In the remaining two, the diseased segment was long and extended to the middle of the descending colon. MacMahon et al. (11) reported finding normal ganglion cells in rectal-suction biopsy specimens but found zonal hypoganglionosis of myenteric plexuses (11). Ariel et al. (10) reported decreased ganglion cells in the myenteric plexuses in the rectum and sigmoid colon of a 16-year-old girl. Ganglia in submucosal plexuses were normal and mature. Howard et al. (7) reported hypoganglionosis associated with a few scattered ganglion cells in the intermyenteric zone that were often associated with findings of hypertrophic nerve trunks. Schärli et al. (8) reported seven cases: five showed hypoganglionosis localized to the descending and transverse colon, whereas two showed involvement of only the small intestine. Other reports in the literature describe hypoganglionosis localized to the colon and rectum (2,3,5,6,9–13). In general, no clear and consistent information on innervation exists in the literature; only one paper reported changes in AchE activity with age (13). All three of our patients had severe symptoms (abdominal distension, bilious vomiting, and enterocolitis) from birth, and all died well before the age of 1 year. Almost all cases reported in the literature occurred relatively late in childhood, and usually involved mild constipation (7,8). Ure et al. (9) reported that only one of their nine patients had ileus, whereas the other eight patients had constipation. Our three patients each had a gastrostomy and jejunostomy, but despite being maintained on parenteral nutrition, each developed severe enterocolitis and died at 4, 4, and 7 months of life. In the literature, Ure et al. (9) reported that seven of their nine patients who underwent resection had histologic evidence of hypoganglionosis. One of these died, four had constipation, one had overflow encopresis, and the other patient had no symptoms. Howard et al. (7) reported that in 17 of their 20 patients, symptoms disappeared after anorectal myectomy alone. Schärli et al. (8) reported that each of their seven patients had good outcome following resection of the hypoganglionotic segment after thorough bowel preparation. Hypoganglionosis a controversial condition because 1) definitive criteria do not exit for diagnosing hypoganglionosis based on the location of pathology or the clinical course; 2) hypoganglionosis occurs in two subtypes, isolated hypoganglionosis and hypoganglionosis associated with HD and intestinal neuronal dysplasia; The transitional segment in HD is often called hypoganglionosis. Thus, hypoganglionosis has been used to describe two different conditions, which causes confusion. Finally, hypoganglionosis also normally exists immediately above the dentate line. We believe that hypoganglionosis should be diagnosed based upon clinical symptoms and the corresponding location of histologic abnormalities. In 1965, Bentley (2) originally described hypoganglionosis in a review of five cases of hypoganglionosis in 22 patients with megasigmoid and megarectum. In 1966, Duhamel and Pages reported two patients with hypoganglionosis, but the location and extent of involvement was not defined (5). In 1968, Ehrenpreis et al. (6) described a patient with colonic hypoganglionosis; however, they did not define the location or extent of the hypoganglionotic segment. The problem with all of these reports of colonic hypoganglionosis is that they lack a description of the exact location and extent of colonic involvement. According to Munakata et al. (13), the abnormal segment in hypoganglionosis is short in most cases, confirming Bentley's findings. Munakata also mentioned that hypoganglionosis proximally throughout the entire small intestine has not been reported (12) with most reports in the literature describing rectal or colonic involvement only; that is, there are few reports of extensive intestinal involvement (8,14). Therefore, in the literature, hypoganglionosis is a condition affecting the colon and rectum (2,3,5–7,9–13) and the histologic feature generally recognized as being pathognomonic of hypoganglionosis is decreased numbers of ganglion cells in myenteric plexuses. Surprisingly, the morphology of the submucosal plexuses has not been reported in detail. This partially explains why it is so difficult to make a definitive diagnosis of hypoganglionosis solely based on examination of mucosal biopsy specimens. In our cases of hypoganglionosis, we found submucosal plexuses were normal despite a decreased number of ganglion cells in myenteric plexuses. Meier-Ruge et al. (1) have emphasized the necessity of analyzing the intramural plexus to make a reliable diagnosis of hypoganglionosis. They recommend a full-thickness rectal biopsy for histologic assessment, and contend that a precise diagnosis may be possible only with multiple open-biopsy specimens. In patients with a clinical picture suggesting hypoganglionosis, the possibility of abnormal myenteric plexuses should be borne in mind despite normal mucosal biopsy findings. Hypoganglionosis may occur as an isolated entity or exist proximal to a segment of typical aganglionosis, the transitional zone in HD. This transitional area where ganglion cells are present in reduced numbers is histologically similar to the entity that Bentley et al. (2) described as hypoganglionosis. Munakata et al. (13) also reported that the histologic findings of hypoganglionosis are quite similar to those of the proximal transitional segment in HD (13). Recently, Schärli et al. (8) suggested that an innervation disorder, otherwise called oligoneuronal disease, may exist on its own or may accompany HD or intestinal neuronal dysplasia. Nevertheless, the hypoganglionosis in HD and isolated hypoganglionosis without HD should be regarded as distinctly different conditions. In hypoganglionosis associated with HD, an absolute decrease in the number of ganglion cells occurs in the submucosal and myenteric plexuses between the aganglionic segment and the normal segment. On the other hand, in isolated hypoganglionosis, the submucosal plexuses seems to be normal, whereas there are decreased ganglion cells in the myenteric plexuses. In our cases of isolated hypoganglionosis, AchE histochemistry showed some positive nerve fibers in the circular and longitudinal muscle layers. However, no positive nerve fibers were seen in the circular and longitudinal muscle layers in hypoganglionosis associated with HD (Fig. 4). As a result, we use the term “hypoganglionosis” to refer only to isolated hypoganglionosis.FIG. 4.: Acetylcholinesterase (AchE) histochemistry. Less AchE activity occurs in the circular and longitudinal muscle layers in the transitional segment of bowel from a patient with Hirschsprung disease (×200). Cm, circular muscle layer; lm, longitudinal muscle layer).Aldridge et al. (15) and Weinberg (16) have shown that a short segment of hypoganglionosis can exist, normally above the dentate line, in infants and children with normal anorectal function. For this reason, knowing the precise location of hypoganglionosis is vital to avoid confusing this normally occurring segment with pathologic segments of hypoganglionosis. When rectal-suction biopsy specimens are examined, the point of biopsy is important to avoid making a diagnosis of hypoganglionosis when in fact the bowel is normal. If patients have very short-segment HD, a rectal-suction biopsy specimen could be taken from the transitional area. The diagnosis of HD could be misdiagnosed as hypoganglionosis and consequently mismanaged. Schärli et al. (8) described seven patients with hypoganglionosis, including two with hypoganglionosis of the entire colon and small bowel who were still dependent on parenteral nutrition after 3 and 9 years, respectively. They reported that extensive bowel resection was not indicated, but that the intestine should be used segmentally for enteral feeding. This may necessitate two or more enterostomies. These patients had clinical courses quite similar to our three patients. Toyosaka et al. (14) reported a poor prognosis with hypoganglionosis, with a mortality rate of 39.2%. Symptoms of functional ileus appeared soon after birth, and were frequently associated with microcolon or narrowing of the left half of the colon. They found that when a long segment was involved, lesions usually involved the entire colon, in particular, the intestine proximal to the ileocecal valve. Two patterns of isolated hypoganglionosis exist. Type A is a mild condition involving a short area in older children; it has a good prognosis when treated conservatively or by surgical intervention (sphincterotomy or pull-through). Type B is a severe condition present from birth, affects the small intestine, and has poor a prognosis even after surgical intervention. All three patients whom we describe in this report have type B. In conclusion, if an infant has signs and symptoms indicative of HD but rectal-suction biopsy findings are normal or inconclusive, an open full-thickness biopsy should be performed to evaluate for isolated hypoganglionosis. Careful investigation of H&E stained specimens and AchE histochemistry are vital. Without detailed histologic assessment correlated to clinical findings, misdiagnosis is likely because many innervation disorders of the bowel are difficult to definitively distinguish. Maturation of ganglion cells, the actual number of ganglion cells, and nerve distribution are important in the differential diagnosis of these bowel motility disorders. Further investigations are necessary to determine whether the degree of abnormally of intramural ganglia is associated with symptoms.