MR Imaging of pial melanosis secondary to a posterior fossa melanotic ependymoma

Abstract

A 36-year-old man presented with trouble speaking and bilateral progressive hearing loss. MR imaging and histopathologic results revealed a posterior fossa melanotic ependymoma. Pial surfaces appeared hyperintense on T1-weighted images and hypointense on T2-weighted images. Histopathologic examination revealed that tumor cells and interstitial spaces had abundant melanin accumulation. There was no evidence of hemosiderin in tumor cells and in interstitial spaces. Pial melanin accumulation secondary to a posterior fossa melanotic ependymoma explained our MR findings.

Fig 1.

Contrast-enhanced (A) and nonenhanced (B) T1-weighted axial MR images reveal a posterior fossa mass that extends cranially through 4th ventricle and left cerebellopontine cistern and caudally through foramen magnum. Nonenhanced T1-weighted sagittal MR image (C) shows that a hyperintense melanin-containing mass displaces the medulla oblongata and spinal cord and extends down to the level of the 6th cervical vertebra. T2-weighted axial MR image (D) shows a heterogeneous posterior fossa mass.

Fig 2.

Four sequential T1-weighted nonenhanced sagittal MR images (A) show linear high signal intensity on the pial surfaces of the cerebrum, cerebellum, brain stem, and spinal cord secondary to pial melanin accumulation (arrows). T2-weighted axial MR image (B) shows striking signal intensity voids on the pial surfaces of brain stem (arrows).

Fig 3.

Photograph of the surgery shows diffuse black and dark brown pigmentation of the pial surfaces of medulla oblongata and medulla spinalis (arrows). C indicates cerebellum; B, bulbus; CS, cervical spinal cord.

Fig 4.

A, Microscopy shows characteristic histopathologic features of ependymoma with true rosettes and pseudorosettes, perivascular orientation (hematoxylin-eosin; original magnification × 200). B, Tumor cells have abundant brown melanin pigment (arrows) in the cytoplasm that shows positivity for Masson-Fontana (original magnification ×100). C, Brown melanin pigment is also present in the interstitial space of the tumor (arrows; hematoxylin-eosin; original magnification ×40).