Malignant peripheral nerve sheath tumour with perineurial differentiation and hyaline eosinophilic globules (thanatosomes): A rare tumour.

Malignant peripheral nerve sheath tumour (MPNST) with perineurial differentiation is a rare variant of MPNST. The pathological features and clinical significance of this variant remain to be characterised. We reported the clinicoradiological and pathological features of a case of recurrent right arm mass related to the ulnar nerve in a 42-year-old female patient. On pathological examination, the tumour showed dual features of conventional and perineurial MPNST which was proven by positive immunostaining for S-100 and EMA. The pathological diagnosis was MPNST with perineurial differentiation. In addition, a peculiar and rare finding of intracytoplasmic eosinophilic hyaline globules (thanatosomes) within tumour cells is reported. We document a rare tumour with hybrid features between conventional and perineurial MPNSTs. Further studies are needed to establish its biological behaviour.