Segmental absence of intestinal musculature in an extremely low birthweight preterm infant

Introduction

The segmental absence of the intestinal musculature (SAIM) or segmental congenital defect of intestine musculature is a rare clinical entity [1], [2], [3]. The first case of the absence of the gastric musculature was described in 1943, by Herbut et al. [2], [4]. SAIM was first reported as a distinct clinical entity in 1967, by Emanuel et al., as a cause of intestinal obstruction [2], [5], [6]. Since then, about 30 cases of SAIM have been described in the medical literature [1], [5], [7].

SAIM is a clinical entity characterised by thinning or complete absence of the muscularis propria with preservation of the mucosa, submucosa and adventitia [1], [8]. It may affect the stomach, the small intestine (often the antimesenteric border of distal ileum) and the colon [2], [3], [4], [5], [6], [9].

SAIM typically presents in the neonatal period, usually during the first 2 weeks of life, as either an intestinal perforation or intestinal obstruction, with or without intussusception [2], [4], [5], [7], [8], [9], [10]. Its aetiology remains unclear, although multiple theories have been proposed [1], [2], [4], [6].

The definite diagnosis can only be rendered through histopathological examination of the resected segment in infants requiring exploratory laparotomy [1], [7], [8], [9]. Prognosis depends on the extent of intestine involved, early diagnosis and prompt surgical treatment [4], [10].

The authors present a case of an extremely low birthweight (ELBW) infant with intestinal obstruction due to a segmental absence of the intestinal musculature.

Case presentation

A 30-week-gestational age (GA) ELBW newborn male was admitted to the neonatal intensive care unit (NICU) and on the fourth day of life presented a progressively acute abdomen.

He was the third son of non-consanguineous parents. The mother had chronic hypertension and her pregnancy was complicated by gestational diabetes and severe pre-eclampsia at 30 weeks and 3 days of GA requiring a caesarean delivery. He was born with a birthweight of 750 g and Apgar score 9/10. He was transferred to the NICU without requiring respiratory or haemodynamic support. In the NICU he underwent umbilical venous and arterial catheterisation and started caffeine citrate and parenteral nutrition. On the third day of life, he started trophic enteric feeding with mother’s breast milk. First meconium elimination was documented in the first 48 hours.

During the fourth day of life, the infant presented high gastric residuals following feedings, progressive abdominal distension and tenderness, and hyperglycaemia (no diarrhoea, bloody faeces, vomiting or cutaneous discoloration; no thermic, respiratory or haemodynmic instability). Blood analysis revealed mild leukopenia and lymphopenia [8.2 × 10⁹/L white blood cells; 0.83 × 10⁹/L (10.1%) lymphocytes], thrombocytopenia (67 × 10⁹/L) and an elevated C reactive protein of 4.0 mg/dL. Abdominal radiography showed marked distension of the intestinal loops and suspicion of intestinal perforation with pneumoperitoneum but without intestinal pneumatosis or portal venous gas (Figure 1). Enteral feeding was interrupted, broad spectrum antibiotic therapy was started, and the infant underwent an emergency laparotomy.

Figure 1:

Abdominal radiographies made on the fourth day of life.

(A) Supine abdominal radiography with marked distension of the intestinal loops and suspicion of intraperitoneal free gas (arrow); no visible intramural or portal venous gas. (B) Cross-table lateral abdominal radiography with suspicion of free gas below the anterior abdominal wall (arrows).

During the surgery, a distended, thin-walled, 7 cm long ileal loop segment was found 10 cm away from the ileocecal valve. Intestinal perforation was not confirmed. The remaining small bowel intestine and colon was normal. The infant was submitted to segmental ileal resection and reanastomosis; surgery was uneventful.

In the immediate postoperative period, he presented transitory haemodynamic instability requiring vasoactive support. On day 11 he successfully re-started breast milk. Parenteral nutrition was withdrawn with 15 days of life. There were no further complications and the infant had a favourable clinical course.

The histopathological examination revealed a small intestine segment with an area of severe hypoplastic muscularis propria; the remaining layers were preserved, with no signs of ischaemia or inflammation; the nervous plexus was in the normal location, number and morphology (Figure 2). It was concluded that this was a case of SAIM complicated with intestinal obstruction.

Figure 2:

Comparation between the histopathological examination of the ileal segment resected and a normal small intestine segment.

(A) Small intestine segment with severe hypoplastic muscularis propria (arrow); remaining layers preserved; no signs of ischaemia or inflammation. (B) Small intestine segment with a normal muscularis propria (arrow). (Microscopy, H&E, 40×.)

Discussion

Segmental absence of intestinal musculature is a rare clinical entity that usually manifests in the neonatal period. It is more frequent in preterm infants, particularly very low birthweight (VLBW) infants, and in infants with severe hypoxia and the need for cardiovascular resuscitation [2], [3], [6], [8], [10].

The precise aetiology of SAIM is still uncertain. The literature presents two main hypotheses: (1) SAIM as a congenital defect (incomplete intestinal myogenesis during embryogenesis, failure of small intestine diverticula resorption, abnormal resorption of the ileal muscle during the regression of the omphalomesenteric duct or familial visceral myopathy); (2) SAIM as an acquired disease (an in utero or after birth ischaemic event causes transmural intestinal necrosis and differences in the mucosa and muscularis propria regenerative capacity result in the exclusive absence of the musculature) [1], [2], [5], [6], [7], [9], [10]. All these possible aetiologies have been supported by different clinical reports but are difficult to prove in the laboratory. Probably, the pathogenesis of SAIM is multifactorial.

In the presented clinical case, it is difficult to determine an exact aetiology. After birth, the infant did not suffer any possible ischaemic event, although in most cases that insult occurs during foetal life. Being an ELBW infant is an important risk factor for acquired SAIM. The absence of local histological scarring and fibrotic changes, normally seen with focal ischaemia, do not support this theory. Therefore, the congenital defect hypothesis must be considered.

The most common presentation of SAIM is intestinal perforation. Obstruction, as seen in this case, may also occur, mostly in adults. Acute abdomen, with moderate to severe abdominal distension, failure to pass meconium and diminished bowel sounds, is the most frequent clinical manifestation. Less commonly, patients may present subacute intolerance to feeding, bilious vomiting and abdominal cutaneous discolouration [1], [8]. Imaging studies often reveal grossly dilated bowel loops, air-fluid levels and, ultimately, pneumoperitoneum [1].

Treatment involves an emergent laparotomy, complete resection of the diseased segment and re-anastomosis or ostomy creation [1], [4], [10]. Whenever possible, primary repair is the procedure of choice, but the decision is multifactorial and depends on the surgeon’s clinical judgment [1], [3]. In the presented case, the paediatric surgery team decided for an immediate reanastomosis, with no complications.

Preoperative diagnosis of SAIM is extremely difficult and its detection during the surgical procedure is nearly impossible [1], [4], [5], [10]. The intraoperative findings may include isolated perforation or a localised area of dilated intestine with an extremely thin wall [1], [7]. However, it is suggested that transillumination of the intestinal wall may be helpful to recognise the defect [1], [4], [5], [10].

Definitive diagnosis is made only after histopathological examination of the resected bowel (intestinal wall devoid, partial or completely, of the external and internal layers of the muscularis propria, but with mucosa, submucosa and adventitia anatomically intact, without signs of inflammation or necrosis) [1], [2], [4], [5], [6], [7], [10]. The disease is typically segmental, affecting an area usually less than 5 cm long [7], [8]. In the presented clinical case, the affected segment was a little longer. If SAIM is suspected, the surgical resection of the abnormal intestine should be complete to prevent recurrent complications and permit the definitive histological diagnosis.

The initial prognosis for this entity was rather poor. However, since 1980, because of improved management and better intensive care facilities, most infants have survived [6]. Early detection of the intestinal perforation or obstruction, immediate surgical treatment and resection of the affected bowel contribute to successful treatment [3], [7].

In summary, SAIM remains a challenging disease with variable clinical presentation and a not fully understood aetiology. The clinicians and pathologists should consider this condition in VLBW infants with progressive acute abdomen and localised intestinal disease (distinct from the more common necrotising enterocolitis), even when an intestinal perforation is not identified. Although most cases of SAIM have been reported in infants with respiratory distress syndrome or haemodynamic instability, this pathology is not always preceded by a postnatal ischaemic event. Progressive compilation of clinical case reports may ultimately yield a more complete understanding of this disease.