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The lesions are usually confined to the terminal part of the ileum and adjacent cecum; the intestinal wall may be thickened with a roughened peritoneal surface. The bowel lumen frequently contains fresh or digested blood (melena). The ileocolic lymph nodes are typically enlarged, 1.0 cm or more in diameter, soft, smooth and gray-white. Occasionally nodes may contain focal hemorrhages. Enlarged lymph nodes may coalesce and encase the ileocolic junction. This lymph-adenopathy may extend more diffusely to involve colonic and jejunal nodes. The mucosa near the ileocecal junction may be congested and thickened but ulcers are not usually visible to the naked eye.

Infantile cortical hyperostosis in rhesus monkeys (Macaca mulatta) is encountered as a congenital enlargement of the diaphyses of long bone. Enlargements, or hyperostoses, are typically hard, bilaterally symmetric and widest at the mid-diaphysis (Fig. 128). The periosteum is mildly to moderately thickened and overlying soft tissues are atrophic, fibrotic and difficult to dissect from underlying bone. Longitudinal sections of long bones reveal morphologically normal epiphysis and physis. Cross-sections through affected diaphyses reveal a relatively normal medullary cavity with discernable cortical bone surrounded by hyperostotic proliferations. Gross features are particularly striking in radiographs (Fig. 129). Lesions are restricted to the musculoskeletal system.