Spindle cell oncocytoma of the pituitary gland
Unrelated initial presentation with falls.
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Large (exceeding 1cm) sellar region solid tumour with suprasellar extension. Heterogeneous hypoenhancement. Adenohypophysis and pituitary stalk are displaced anteriorly. Optic chiasm displaced and bowed superiorly.
The patient went on to have surgery.
Moderately cellular. Proliferation of spindle cells with abundant eosinophilic, focally granular cytoplasm. Cells arranged in loose vesicular architecture, and in other areas in haphazard arrangement. Marked variation in nuclear size and shape, with numerous cells showing marked nuclear enlargement with irregular nuclear outlines and prominent nucleoli. No mitotic activity.
Lymphoplasmacytic cell infiltration. Large tumour cells seen to lie within neutrophil-like stroma.
Positive for: S-100, TTF-1, vimentin.
Very focal EMA staining. Patchy GFAP staining. Patchy and weak staining for CD68.
Negative for synaptophysin.
Variable Ki-67 index, but less than 5%.
Final diagnosis: Spindle cell oncocytoma. WHO Grade 1.
Comment: Granular cell tumour, pituicytoma, and spindle cell oncocytoma would all show evidence of pituicyte as the cell of origin. These 3 tumours may represent a morphologic spectrum of one entity. Spindle cell oncocytoma is the most likely of these lesions to show nuclear pleomorphism.
On imaging, this would be called a pituitary macroadenoma more than 99.9% of the time.
Craniopharyngioma and, in this age group, metastasis, can be DDx. The fact that the adenohypophysis and stalk are displaced anteriorly are unusual, but would probably not be sufficient to sway the diagnostician towards other extremely rare pituitary gland tumour.
The tumour has nevertheless succeeded in distracting the radiologists into missing the AComm aneurysm over multiple studies.