Benign metastasizing meningioma

Dear Editor, Meningiomas are typically considered benign and intracranial neoplasms. However, they can rarely appear in extracranial regions, originating even from initially diagnosed low-grade tumors. Here, we report a rare case of benign metastasizing meningioma of the skin. A 69-year-old Asian male presented to our hospital with an asymptomatic flesh-colored nodule on the left perinasal region, which had slowly grown over a decade [Figure 1a]. His medical history included hypertension, hyperlipidemia, chronic kidney disease stage 3, and an 18-year history of left sphenoidal ridge meningioma. Sixteen years before presenting to our hospital, the patient underwent partial resection and radiotherapy for the meningioma. Achieving complete eradication was difficult due to its precarious location, resulting in residual meningioma remaining in the left cavernous sinus region. Three years prior, another partial resection was performed due to enlargement and the resulting mass effect of the residual meningioma causing severe headache. Pathology reports confirmed World Health Organization (WHO) Grade 1 transitional meningioma. There was no relapse during the 3-year follow-up period.Figure 1: (a) Clinical presentation: A 7 mm × 8 mm, well-defined, asymptomatic, and slowly enlarging flesh-colored nodule with elastic consistency on the left perinasal region; (b) Dermoscopic finding: A yellow-orange structureless area; (c-e) Histopathological findings of whorls and nests of meningothelial cells with occasional intranuclear pseudoinclusions (black arrow) in the dermis and subcutis; (f and g) The meningothelial cells showing strong immunostaining for epithelial membrane antigen (EMA) (f) and somatostatin receptor 2A (SSTR2A) (g). (c) H and E stain, ×25, (d) H and E stain, ×100, (e) H and E stain, ×400, (f) EMA stain, ×50, (g) SSTR2A stain, ×50.On physical examination, the skin nodule appeared well defined, measuring 7 mm × 8 mm, and was elastic, nonmovable, and nontender. The subsequent dermoscopy revealed a yellow-orange structureless area [Figure 1b]. An excisional biopsy of the nodule was performed. Histological examination of the skin biopsy revealed infiltrative nests of neoplastic meningothelial cells with occasional intranuclear pseudoinclusions, forming abundant whorls in the dermis and subcutis [Figure 1c-e]. The growth, including lobular and fascicular patterns, was consistent with the transitional subtype of meningioma. The lesion exhibited the same benign histological grade as the preexisting intracranial meningioma, classified as WHO Grade 1. Immunohistochemical studies of the lesion showed positivity for epithelial membrane antigen and somatostatin receptor 2A [Figure 1f and g] and negativity for S100, P40, and glial fibrillary acidic protein. Magnetic resonance imaging of the skull revealed no direct extension of the intracranial meningioma to the skin lesion [Figure 2]. Therefore, this cutaneous meningioma was classified as distant metastatic meningioma. Based on its benign histological features and resemblance to the original tumor, the final diagnosis was “benign” metastatic meningioma of the skin.Figure 2: T2-weighted magnetic resonance imaging showed no direct extension of the intracranial meningioma (red arrow) to the skin lesion (red circle).Cutaneous meningiomas are categorized into three types based on their etiology. Type I lesions are congenital, arising from ectopic arachnoid cells trapped in the dermis and subcutis during embryologic development. Type II and III lesions are acquired forms, with Type II lesions developing from ectopic arachnoid cells along cranial and spinal nerves, often without a corresponding meningioma in the neuroaxis. Type III lesions arise from meningeal tumors that secondarily involve the skin through direct extension or cutaneous metastasis.[1] Our case exemplifies a Type III cutaneous meningioma metastasizing from an intracranial meningioma. The WHO classifies meningiomas into three histological grades: grade 1 (benign), Grade 2 (atypical), and Grade 3 (anaplastic). Higher grades are associated with more malignant behavior, including metastatic potential and recurrence. Most meningiomas are WHO Grade 1, accounting for 85%–95%, characterized by a low mitotic index, fewer than 3 atypical features, and no brain invasion.[2] Meningioma metastasis is uncommon, reported in approximately 0.1% of patients, primarily in WHO Grade 3 tumors.[3,4] However, even WHO Grade 1 meningiomas can metastasize, with the metastases often being benign.[3,4] Benign metastasizing meningiomas are extremely rare, the incidence of which remains unclear. The mean period until metastasis is significantly longer for Grade 1 (11 years) compared to Grades 2 (5.4 years) and 3 (2 years).[5] Common metastatic sites include the lung, bone, and liver,[6] with rare reports of skin metastasis. In our thorough literature search, there are currently fewer than thirty previous case reports of skin metastasis, with the majority being WHO Grade 2 and most commonly located on the scalp [Supplementary Table 1].The causes of extracranial metastases from Grade 1 meningiomas are largely unknown, although potential explanations include tumor invasion into venous sinuses leading to hematogenous spread or iatrogenic seeding during resection which can spread through the lymphatics and venous sinuses.[5,6] Prognosis after metastasis varies with the WHO grade of the distant metastasis. In a previous report, only one death with an unknown survival time was noted for Grade 1, with no other deaths recorded during the observation period. However, for Grades 2 and 3, the mean survival times were 3.3 and 0.98 years, respectively.[5] Due to the rarity, there is no established consensus regarding the staging and treatment of metastatic meningiomas.[7] Local treatment options include surgical resection and radiotherapy, while systemic management options such as antiangiogenic medications and immunotherapy are being investigated.[8] In conclusion, we here present a rare case of meningioma metastasizing to the skin. Dermatologists should consider cutaneous meningioma as a potential diagnosis in patients with a history of intracranial meningioma or neurological signs and symptoms. Ethical approval This study was conducted in accordance with the Declaration of Helsinki and was approved by the Institutional Review Board of Chang Gung Medical Foundation, approval number:2403140040, approval date: 2024/04/30. The patient consent was waived by the IRB. Data availability statement The datasets generated during and/or analyzed during the current study are publicly available. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.