SID is a rare congenital anomaly characterized by sharply demarcated dilatation of gastrointestinal tract without any evidence of mechanical obstruction . The most common localization of dilated segment is the ileum and followed by the colon, jejunum, and duodenum [6,7]. Approximately half of the SIDs present in the first day of life . Rarely, some cases become symptomatic during infancy and adolescence. SID is encountered in both sexes with a slight male predominance . The most common clinical presentation is intestinal obstruction, and abdominal pain, anemia, and failure to thrive can be seen in older children . Anemia is the first sign of SID in patients with heterotopic gastric mucosa. It has been reported that one third of SID cases have been detected incidentally during laparotomy . Omphalomesenteric remnants and malrotation are reported as associated anomalies in SID. Malrotation associated with SID was also recognized in our patient during laparotomy.
Although diagnostic criteria are well established, the etiology of the disease is unclear. It has been suggested that transient embryonic structures such as vitelline vessels and omphalomesenteric bands cause extrinsic compression of both ends of bowel [9,10]. In addition, in utero vascular accidents, primary aplasia of an intestinal segment, and congenital damage to the nerves in myenteric plexus are considered as possible causes of SID . The role of enteric nervous system and interstitial cells of Cajal was also investigated, and no neurogenic etiology could be attributed to SID . We have also detected normal distribution of interstitial cells of Cajal in our case.
SID can also be detected as an intra-abdominal cystic mass in prenatal ultrasonography . On abdominal X-ray, it is associated with dilated bowel loops with or without air-fluid levels and can be easily misdiagnosed as other causes of intestinal obstruction . As in our case, contrast enema studies can be performed to differentiate other gastrointestinal anomalies. Contrast enema studies show marked segmental dilatation of small bowel loop with normal colon findings. Since most of the neonates undergo contrast enema studies, the use of computed tomography in the diagnosis of SID is limited and reserved for older patients.
The treatment of SID is resection of dilated segment and end-to-end anastomosis . Most patients have uneventful course, and prognosis is excellent after surgical resection.
In most of the cases, histology of the resected segment is usually normal . However, some of the cases showed hypertrophied or very thin muscle layer in the involved segment in histopathological evaluation. Heterotopic esophageal or gastric mucosa or cartilaginous foci are also reported in dilated intestinal segment . Kobayashi et al. suggested that ectopic gastric mucosa causes interruption in the neural and muscular network in the dilated intestine . However, all resected segments show normal presence of ganglion cells in myenteric and submucosal plexuses . Histopathological recognition of localized vacuolization of the smooth muscle layer has suggested that myopathy might contribute to the pathogenesis of SID . However, there are no reports of additional smooth muscle layer in the involved segment of SID in the literature. In the case reported here, no mucosal abnormality was present, ganglia and plexuses were normal in distribution, and there was no vacuolization in smooth muscle layer.
Architectural malformations of muscularis propria consist of supernumerary and/or haphazard orientation of muscle fibers with an additional neural plexus. Smith et al. have described supernumerary muscle coat in five patients and classified them as diffuse or segmental . SIMC is also reported in a patient with Hirschsprung disease and considered as a congenital anomaly rather than an acquired histopathological alteration . X-linked intestinal pseudo-obstruction due to filamin A mutation should be also considered in the differential diagnosis of SMIC. Kapur et al. reported FLNA mutations with intestinal pseudo-obstruction. They usually show male predominance, short small intestinal length, and malrotation . FLNA mutations include abnormal intestinal layering throughout a longer segment of the intestine with neurologic impairment in histology. In our patient, abnormal layering is limited to a short segment of the intestine, with normal ganglia and without associated neurologic disease. In our case with SID, we have found segmental SIMC in the dilated segment. There was no vacuolar change in the muscle layers, but haphazard orientation was remarkable in some areas. Myenteric plexuses and ganglion cells were normally placed between the inner circular layer and the longitudinal layer, but some plexuses were also present between the longitudinal layer and the outermost circular extra smooth muscle layer. Although the role of myopathy was suggested in the etiology of SID, SIMC as a cause of SID has not been reported previously. We suggest that hypertrophied muscle or very thin muscle layer should be considered as result rather than the cause of SID . SIMC or architectural malformation of the intestinal smooth muscle should be considered as the most likely cause of segmental dilatation. Presence of myenteric plexuses and ganglion cells towards the external surface also supports that this is a primary developmental problem.