Claudin-1 and Glucose Transporter 1 Immunolabelling in a Canine Intraneural Perineurioma

A 4-year-old male leonberger was diagnosed tentatively with a peripheral nerve sheath tumour of the median nerve based on neurological examination, electrodiagnostic testing and ultrasound evaluation. The lesion was excised and submitted for pathological examination. Histopathology revealed an irregularly enlarged, hypercellular nerve fascicle with neoplastic tissue consisting of a uniform population of spindle-shaped cells arranged in 'pseudo-onion bulb-like' whorls around axons. Minimal anisocytosis and anisokaryosis were present, together with a low mitotic index. Electron microscopy showed spindle cells with a discontinuous basal membrane and intercellular junctions, as well as pinocytotic vesicles. Immunohistochemistry for neurofilament, S100 and glucose transporter 1 was negative, whereas labelling for claudin-1 and laminin was positive. Based on these observations, a definitive diagnosis of intraneural perineurioma was made.