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A 52-year-old man presents with neurologic signs suggesting a right hemispheric brain lesion. MRI demonstrated an extra-axial right parietal mass measuring 12.0 cm in greatest dimension. There was compression of the underlying cortex with a right-to-left midline shift. The overlying calvarium did not show bony involvement by the mass. The tumor was resected and grossly appeared red-brown and gelatinous.
Archive Case and Diagnosis:
This case first appeared as Performance Improvement Program in Surgical Pathology (PIP) 2008, Case 13, and is chordoid meningioma.
Criteria for Diagnosis and Comments:
The microscopic sections show a heterogeneous tumor with pools of myxoid matrix, syncytial cords of cells, and stellate cells intermixed with more solid areas composed of plump spindle cells assuming a “whorled” pattern. The nuclear features of both the spindle cells and cells situated in myxoid stroma are similar and show elongation with delicate “bubbly” or vesicular chromatin and inconspicuous nucleoli. Mitotic figures are rare (< 4 per 10 hpf). The more solid and whorled areas are typical of meningioma and the presence of myxoid matrix and chordoma-like cells warrant classification as the chordoid subtype of meningioma.
Chordoid meningioma is uncommon (<1% of all meningiomas), but distinguishing it from other subtypes is important because of the high rate of local recurrence compared to conventional meningiomas (meningothelial, transitional, fibroblastic). Consequently chordoid meningioma is considered a grade II tumor in the W.H.O. classification, with a prognosis similar to atypical and clear cell meningioma subtypes. Conventional meningiomas are considered grade I tumors in the W.H.O. system.
Like other meningiomas, the cells in chordoid meningioma are positive for EMA and vimentin, but negative for keratin, GFAP, and S-100. Prominent lymphoplasmacytic infiltration is often seen, sometimes with lymphoid follicles. Chordoid meningioma can occur anywhere along the dura mater, including the skull base, but (unlike chordoma and myxoid chondrosarcoma) bony involvement is exceptional. Though they are dural-based lesions, they can invade brain parenchyma. Because of their abundant matrix, they can also reach considerable size and may appear to grow faster than other meningioma types. Because of their delicate supporting stroma, they also often show intratumoral hemorrhage and hemosiderin.
Typical areas of meningioma are always present in chordoid meningioma (the main criterion for diagnosis), but the abundant intermingled myxoid matrix and non-typical meningioma cells can be mistaken for a number of similar-appearing lesions, especially in biopsy material.
As the namesake for this subtype of meningioma, chordoma is a close mimic of the myxoid areas in chordoid meningioma. Chordoid meningiomas may arise in the skull base region, but chordoma always occurs there with an epicenter around the clivus and sella turcica. The right parietal location of the tumor in this case essentially excludes chordoma from consideration. Chordoma cells do classically have more vacuolated cytoplasm and lack the nuclear features of meningioma. Although more densely cellular areas can also be seen, whorling is not common in chordomas. Unlike meningiomas, chordomas show keratin, S-100 protein and Glut1 expression, though they are also positive for EMA.
Myxoid or chondroid sarcomas
These lesions lack areas of typical meningioma and have a greater propensity for bony permeation. Areas of true chondroid differentiation are not seen in chordoid meningioma. Unlike chordoid meningioma, these lesions would not be expected to show expression of EMA.
Mucin producing carcinomas may also resemble chordoid meningioma; though they would likely show greater cytologic atypia without the nuclear features described above and, again, lack areas of classic whorled meningioma. Their keratin profile as well as any tissue specific antigen expression would also be of diagnostic utility.
Chordoid glioma is a very rare tumor of the CNS, and is restricted to around the 3rd ventricle. Like all gliomas, they are strongly GFAP positive.