Schwannosis with mature collagen in the spinal cord of a calf.

Schwannosis is a rare syndrome in which Schwann cells ectopically invade and proliferate within the CNS, often resulting in myelination of central axons. A 1-mo-old, male Holstein-Japanese Black crossbred calf with wry tail had hindlimb paresis and urinary incontinence from birth. A subpial plaque-like mass was located in the dorsal funiculi of the sacral spinal cord. The mass was composed of nerve bundles containing axons surrounded by spindle cells, admixed with abundant fibrous connective tissue. No prominent changes were observed in the surrounding tissue. Immunohistochemically, the spindle cells within the nerve bundles were immunolabeled with anti-myelin protein zero and anti-S100 but lacked immunolabeling with anti-myelin basic protein, suggesting that these cells were immature Schwann cells. Our case is an unusual mixture of immature Schwann cells and mature collagen without evidence of atypia or spinal cord injury. We hypothesize that this lesion resulted from the aberrant incorporation of Schwann cells and mature collagen fibers into the spinal cord during embryonic development.