Granulofilamentous meningioma

Abstract

A 55-year old female was referred to the Department of Neurosurgery, Kitasato Hospital, because of a hearing impairment. Neuroimaging revealed a typical meningioma attached to the falx in the right frontal region. During surgery, an encapsulated, circumscribed, reddish-gray, slightly hard tumor attached to the falx was completely removed by an interhemispheric approach. On light microscopy, many of the tumor cells contained eosinophilic inclusions with single or multiple vacuoles that displaced the cytoplasm. The nuclei of the tumor cells were eccentric. There were no signs of malignancy in the specimen. Electron microscopy revealed that most of the eosinophilic inclusions were composed of filaments measuring 12 nm in diameter. There have been several reports of benign meningiomas with eosinophilic inclusions composed of intermediate filaments. The microscopic differences between these types of tumor and rhabdoid meningiomas are very subtle, and it is important the two types of tumors are not confused. Benign meningiomas with eosinophilic inclusions comprising intermediate filaments, for example the tumor described in this report, have been diagnosed as granulofilamentous meningiomas, which is a subtype of benign meningioma.

Intraoperative touch cytology for an orbital tumour

“…Conversely, although granulofilamentous meningiomas also have eccentric nuclei and eosinophilic globular inclusions, vacuoles are often included in their inclusions . Furthermore, they have an inconspicuous cell border, no cellular atypia, rare mitosis and no necrosis . By electron microscopical analysis, inclusions of granulofilamentous meningioma are observed as an electron‐dense granular inclusion with vacuole and attached by intermediate filaments .…”

“…In addition, necrosis and frequent mitotic figures are found in rhabdoid meningiomas at a median number of 5/10 high‐power fields . Conversely, although granulofilamentous meningiomas also have eccentric nuclei and eosinophilic globular inclusions, vacuoles are often included in their inclusions . Furthermore, they have an inconspicuous cell border, no cellular atypia, rare mitosis and no necrosis .…”

“…Therefore, granulofilamentous meningiomas can be differentiated from AT/RTs on the basis of immunohistochemistry. The electron microscopic features of AT/RT inclusion are described as whorled bundles of intermediate filaments, whereas those of granulofilamentous meningioma are observed as an electron‐dense granular inclusion with a vacuole and attached by intermediate filaments …”

“…In conclusion, although granulofilamentous meningioma is not widely recognised, it is necessary to accurately distinguish among granulofilamentous meningiomas (WHO grade I), rhabdoid meningiomas (WHO grade III) and AT/RTs (WHO grade IV) to predict the prognosis and frequency of recurrence, and the need for postoperative radiation therapy. In particular, the two variants of meningiomas with globular inclusions demonstrate the aggressiveness of different ends of the spectrum . Therefore, a differential diagnosis, particularly with intraoperative frozen‐section studies and cytology, is important.…”

“…In addition, histopathologically, they proliferate with whorl formation. Therefore, this tumour can be considered as a benign meningeal tumour with intracytoplasmic globular inclusion, granulofilamentous meningioma . Question 2Answer: a and d This tumour is a benign meningeal tumour and shows no necrosis . The neoplastic cells proliferate with syncytium‐like sheets with an indistinct cell border and often form whorl structures.…”