Presentation
Five months constant neck pain. An MRI cervical spine was initially performed which demonstrated a posterior fossa abnormality. MRI brain was subsequently performed.
Patient Data
Bilobed extra-axial mass of the right posterior fossa crossing the tentorium cerebelli. The inferior, larger component of the mass is peripherally low signal on T2 with internal high T2 components. The superior component is markedly hypointense on T2 and hyperintense to grey matter on T1. The mass has facilitated diffusion and avid, heterogenous enhancement. Associated mass effect on the right cerebellar hemisphere and compression of the 4th ventricle. No hydrocephalus.
Case Discussion
The patient went on to have a resection.
Histology
Sections show lesional tissue composed of areas of sclerosis and hypocellularity and areas of moderate cellularity. The lesional cells are bland with inconspicuous cytoplasm and wavy nuclei with tapered ends. The cells are arranged in short fascicles with some storiform pattern, separated by collagen bands. The vascular spaces are ectatic. Focal islands of entrapped meningothelial cells are present. There is no necrosis or nuclear pleomorphism. Mitotic count numbers at 1 per 50 high power fields. By immunohistochemistry, the lesional cells expression STAT6. There is no expression of EMA, PR or Sox10 (entrapped meningothelial cells show normal EMA and PR staining).
Final diagnosis: solitary fibrous tumor, WHO grade I
Discussion
This case demonstrates a common location for solitary fibrous tumor of the dura, as well as the "yin yang sign".