Which One is The Real Zebra

A repeat MRI showed an interval decreased thickening and enhancement of the infundibulum and sellar contents. Due to steroid related side effects, a rheumatologic consultation was obtained for consideration of steroid sparing agents and a re-review of the pathology was requested. Additional H&E stain recuts and immunohistochemical stains were performed for CD1a, 3, 4, 5, 8,10,20,68, 79a, 138, BCL1&6 and Ki67. Pathology showed an atypical lymphoid aggregate composed of CD20, CD 79a+ B cells with focally high Ki67 index, negative kappa and gamma staining. A very small focus of cells on the biopsy was seen which looked atypical although given the rarity of diagnosis, it was difficult to determine whether they were part of the inflammatory process or whether they represented a small focus of neoplastic cells. Given the lack of radiographic progression seen on MRI and modest response to steroids it was felt that this was an aggressive form of LYH. The patient was started on steroid sparing agents. Over the next 8 weeks he received mycophenolate, plasmapheresis, rituximab, and cyclophosphamide. After initial stability the vision progressively declined to 20/150 in the left eye with presence of bilateral visual field defects. An MRI scan continued to show stable enlargement of the pituitary stalk and the optic chiasm. The slides were sent to the National Cancer Institute for another opinion. CD-117 (c-kit) immunostaining was performed on the destained H&E section. The large atypical cells were strongly positive for CD 117 consistent with a CNS germinoma. A repeat metastatic work up was negative including negative lumbar puncture for cytology and tumor markers and a negative brain and spine MRI. The patient underwent proton radiation therapy and vision stabilized at 20/20 in the right eye and 20/80 in the left eye at last follow up visit.