Primary extracranial meningiomas of the nasal cavity are extremely rare. To date, about 36 cases have been reported [5
]. The origin of PEMs is unclear. PEMs are thought to arise from undifferentiated mesenchymal stem cells that get trapped or misplaced in intraosseous locations [13
]. Conceivably, PEMs could arise from undifferentiated arachnoid cap cells associated with blood vessels or cranial nerves traversing the skull [14
Atypical meningioma is a rare variant. According to WHO criteria, meningiomas are classified into three grades. Most meningiomas are benign (WHO Grade I); 5–15% of meningiomas are atypical (WHO Grade II); and 1–2% are anaplastic/malignant (WHO Grade III) [15
Atypical meningiomas are diagnosed when increased mitotic activity (defined as ≥4 mitoses/10 HPF) or three or more of the following features are encountered: increased cellularity, small cells with a high nucleus:cytoplasm ratio, prominent nucleoli, uninterrupted patternless or sheet-like growth, and necrosis [16
Malignant meningiomas (WHO Grade III) exhibit histological features of malignancy, including obviously malignant cytology (e.g., an appearance similar to sarcoma, carcinoma, or melanoma) and/or a high mitotic index (≥20 mitoses/10 HPF) [16
]. Moreover, malignant meningiomas are usually fatal and have a higher rate of recurrence and metastasis [15
] than the benign variant. Perry et al. [17
] showed that the median survival time for malignant meningiomas was 1.5
years, with a 5-year mortality rate of 68%.
The incidence of metastases in meningiomas is very low. Although surgical removal may increase the risk of iatrogenic metastases of histologically aggressive meningiomas [18
], malignant meningiomas can disseminate with no previous surgery [19
]. The reported incidence of distant metastases in malignant meningioma is around 43% [20
]. The mode of metastatic spread is unclear. Three possible dissemination patterns have been described: hematogenous, lymphatic, and via the CSF [20
]. In PEMs, the likely routes of distant metastases are venous and lymphatic, because PEMs have no intracranial attachments. Metastasis via the venous system usually causes pulmonary, hepatic, and skeletal metastases, while that via the lymphatic system causes lymph node and subcutaneous metastases [21
]. In this case, distant metastases were seen in the anterior chest wall and scalp 2
months after local recurrence. However, with time, multiple subcutaneous tumors developed over the entire body, so it is possible that distant metastasis to vital organs, such as the lungs or liver, occurred.
We presented the case of a middle-aged male with distant metastasis from a PEM of atypical histology originating from the nasal septum. Although classified histologically as atypical, the meningioma exhibited unusually aggressive behavior and transformed to a malignant meningioma after surgery. Additionally, it is known that meningiomas tend to become more histologically aggressive with each recurrence [21
]. In our case, this clinical characteristic was seen.
Currently, complete surgical excision of PEMs is the treatment of choice and there is no need for adjuvant treatment [11
]. However, our case showed that tumors invade adjacent septal cartilage, and it has been reported that adjuvant radiotherapy contributed significantly to improvements in overall survival and recurrence-free survival in intracranial meningiomas with local tissue invasion [22
]. Given their anatomical complexity and the fact that they are covered with mucosal epithelium, which has many vascular and lymphatic channels, PEMs in the nasal cavity have a higher risk of incomplete tumor resection. Therefore, routine postoperative adjuvant radiotherapy and careful postoperative imaging may be necessary to improve the outcome in patients with atypical PEMs in the nasal cavity.