Necrotizing Enterocolitis (NEC, Neonatal Necrotizing Enterocolitis)

General: May develop as a complication of specific clinical problems, such as Hirschprungs disease, severe diarrhea, hypothermia, asphyxia/hypoxia, etc. May vary from relatively mild distension, diarrhea, & bleeding to septicemia, shock, and perforation. The most reasonable and reliable investigation is detection of gas in the gut wall &/or intrahepatic veins on imaging, though ~15% of patients will be false negative. Most pathologic examinations have been of fulminant NEC following colectomy, at autopsy, or following resolution and repair, thus biopsy diagnosis is not well defined. It most commonly affects the terminal ileum and adjacent colon, though any portion of the gut may be involved.

Gross: Dusky or frankly hemorrhagic, with variable ulceration of the mucosa (although at surgery a dusky serosa may mean transient ischemia or congestion rather than necrosis; intra-operative histologic evaluation used to help minimize resection). Areas of deep mural necrosis may show marked mural thinning. Perforations are present in ~50% of pathologic specimens. Multiple discrete areas of involvement are present in about half of patients.

Microscopic: In mild cases necrosis (coagulative) is confined to the mucosa, but may progress to transmural necrosis and perforation. Necrosis is associated with hemorrhage, intramural vascular thrombi (assumed in the case of NEC to be secondary), and hydrogen containing vacuoles in the wall due to bacterial production. Acute inflammatory infiltrate may be surprisingly minimal versus the amount of hemorrhage and necrosis, though it increases as lesions progress. Healing is evidenced in ~66% of cases, manifested by granulation tissue and re-epithelialization of ulcers. Healing may lead to a relatively normal colon, permanent mural fibrosis with architectural distortion or stricture/obstruction, or aganglionosis.

Stains:

• Positive:
• Negative:
• Suggested, focused panel:

((()))Perspectives in Pediatric Pathology: Gastrointestinal Diseases. #20, 1997.

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