Primary central nervous system extranodal NK/T-cell lymphoma predominantly composed of anaplastic cells: A case report

Extranodal NK/T-cell lymphoma (ENKTL) of the central nervous system (CNS) is very rare. We herein report a case of ENKTL originating from the CNS in a 79-year-old woman. The patient presented with episodic seizures, left-sided limb weakness, altered mental status, and dysarthria for more than 1 month. Radiological examination revealed a solitary mass in the (laterality) frontal lobe of the brain, which was surgically removed. Histopathology revealed a tumor showing diffuse growth of large anaplastic cells with multiple reniform nuclei, horseshoe nuclei, and doughnut-like nuclei. Immunohistochemically, the tumor cells were diffusely positive for CD3, CD30, Gramazyme B, and TIA1 and negative for ALK and CD56. It was almost misdiagnosed as ALK-negative anaplastic large cell lymphoma, but positivity for cytotoxic markers and EBER-ISH helped establish the diagnosis of ENKTL. To the best of our knowledge, this anaplastic variant of ENKTL has not been reported in the CNS. We present this case to describe an uncommon aggressive variant of ENKTL at CNS as a rare location with diagnostic pitfalls.