高位円蓋部発生原発性硬膜外髄膜腫の1例—症例報告と文献的考察

A Case of Primary Extradural Meningioma Located at the High Convexity:A Case Report and Review of the Literature

Ⅰ．はじめに

　髄膜腫の多くは，硬膜内に発生する¹²⁾．一方，稀ながら硬膜外に発生する髄膜腫も存在し^2,4,7-9)，それらは原発性硬膜外髄膜腫と呼ばれている⁷⁾．今回われわれは，intraosseous typeと思われる原発性硬膜外髄膜腫の1例を経験した．本例を呈示し，かつ原発性硬膜外髄膜腫の臨床的事項に関し，文献的考察を加えて報告する．

　OBJECTIVES:Primary meningiomas arising outside the intracranial component are rather rare and have been termed primary extradural meningiomas（PEMs). We present a case of an intraosseous-type PEM occurring at a high convexity location and discuss the clinical characteristics of PEMs.

　CASE:An 80-year-old woman presented with a soft and painless subcutaneous mass of approximately 10 cm in diameter in the right parietal region, which had appeared 1 year previously. Mild cognitive dysfunction and left hemiparesis were observed upon admission. A skull radiograph and a bone window computed tomography scan revealed an osteolytic lesion at the above-mentioned site. Magnetic resonance imaging indicated that the mass was inhomogeneously enhanced and seemed to extend through the skull defect both intra- and extra-cranially. The preoperative diagnosis was a metastatic skull bone tumor due to the patient's history of breast cancer. During surgery, the tumor was found to be solid and had expanded through both the inner and outer tables of the skull, destroyed the inner table at one location, and perforated into the subdural space via the thinned, but not infiltrated, dura mater. The tumor was removed along with a wide margin of surrounding healthy bone and a cranioplasty was performed using a titanium plate. The histopathological diagnosis was atypical meningioma（World Health Organization grade Ⅱ). Postoperatively, no adjuvant therapies（radiation and/or chemotherapy）were administered and the patient was reported to be well at 8 months post-surgery with no evidence of tumor recurrence.

　CONCLUSIONS:Although PEMs are rather rare, clinicians should consider the differential diagnosis of osteolytic skull vault tumors.