Soft tissue
Peripheral nerve
Other benign
Ectopic meningioma
Authors: Azfar Neyaz, M.D., Rana Naous, M.D.
Editorial Board Member: Laura Warmke, M.D.
Deputy Editor-in-Chief: Borislav A. Alexiev, M.D.
Last author update: 3 March 2025
Last staff update: 3 March 2025
Copyright: 2019-2025, PathologyOutlines.com, Inc.
PubMed Search: Ectopic meningioma
Table of Contents
Definition / general | Essential features | Terminology | ICD coding | Epidemiology | Sites | Pathophysiology | Etiology | Clinical features | Diagnosis | Radiology description | Radiology images | Prognostic factors | Case reports | Treatment | Gross description | Gross images | Frozen section description | Microscopic (histologic) description | Microscopic (histologic) images | Cytology description | Cytology images | Positive stains | Negative stains | Electron microscopy description | Molecular / cytogenetics description | Sample pathology report | Differential diagnosis | Additional references | Practice question #1 | Practice answer #1Cite this page: Neyaz A, Naous R. Ectopic meningioma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/softtissueectopicmeningioma.html. Accessed September 25th, 2025.
Definition / general
- Ectopic (extracranial) meningiomas are morphologically identical to their central nervous system (CNS) counterparts and characterized by the proliferation of meningothelial cells in syncytial nests with whorl formation and occasional psammomatous calcification; by definition, they occur in the absence of any intracranial / intraspinal connection or extension
- Meningothelial hamartomas are collections of nonneoplastic meningothelial / arachnoid cells and represent a developmental rest
Essential features
- Ectopic meningiomas most commonly occur in the head and neck region, followed by mediastinal / thoracic and paravertebral locations
- Morphologic features, including different histologic patterns, immunohistochemical features and tumor grading, are identical to their CNS counterpart
- They usually follow a favorable course after complete surgical resection; however, intraosseous skull based lesions show a relatively higher propensity for local recurrences
- Meningothelial hamartoma is a benign developmental rest commonly found in the scalp, lung and lymph nodes and cured with surgery alone
Terminology
- Ectopic meningioma: extracranial / extraspinal meningioma, extraneural meningioma, extradural meningioma, cutaneous meningioma, calvarial meningioma, heterotopic meningioma, intraosseous meningioma
- Meningothelial hamartoma: meningothelial rest, meningothelial choristoma, meningothelial heterotopia, meningothelial proliferation, meningothelial nodule
ICD coding
Epidemiology
- Ectopic meningioma is extremely rare, with an incidence rate of ~1% of all meningiomas (Int J Surg Pathol 2019;27:457)
- Most of the available literature suggests it has a predilection for younger adults compared to its CNS counterpart; however, some literature suggests bimodal age distribution (commonly second decade and fifth to seventh decades) (J Neurosurg 2000;93:940)
- There is a slight female preponderance
- Meningothelial hamartomas are most commonly reported in infants and young children
- Meningothelial nodules are frequently encountered incidentally in resected lung specimens
- There is no racial or gender predilection
Sites
- Most commonly affected location is the head and neck region, with the most commonly reported intraosseous sites being skull bones, maxilla and mandible, while among soft tissue, scalp, sinonasal tract, middle ear, orbit and oral cavity are the most commonly affected locations (Head Neck Pathol 2016;10:95, Head Neck Pathol 2009;3:116)
- Outside of head and neck region, lung, mediastinum / thoracic, paraspinal and cutaneous locations are the most commonly reported sites (World J Clin Cases 2022;10:4196, Head Neck Pathol 2009;3:116)
- Other exceptionally rare sites are the kidney, retroperitoneum, adrenal gland and extremities
- Meningothelial hamartomas can present as a solitary mass in the scalp and have been described commonly in lung and lymph nodes (Am J Dermatopathol 2022;44:602)
Pathophysiology
- A few reports of familial syndromes (neurofibromatosis type 2, Cowden syndrome and Gorlin syndrome) associated with ectopic meningioma have been reported (Am J Dermatopathol 2022;44:e39)
Etiology
- Pathogenesis is not fully understood; however, the following 4 hypotheses have been proposed (Head Neck Pathol 2009;3:116)
- Arises from ectopic arachnoid cells present in peripheral nerve sheaths, since meningothelial cell clusters are found beyond the points of dura penetration
- Arises from pluripotent mesenchymal cells
- Misplacement or migration of meningothelial cells from intracranial locations during embryogenesis or entrapment during closure of midline structure
- Traumatic displacement of meningothelial cells
- Pathogenesis of meningothelial hamartoma in the head and neck region is suggested to be similar to meningoceles and meningoencephaloceles
Clinical features
- Symptoms are not specific and vary greatly depending on the involved location
- Overall, the most common presentation is a slow growing, painless mass
- Scalp lesions can give rise to alopecia and tenderness
- Reference: Rom J Morphol Embryol 2023;64:467
Diagnosis
- Imaging modalities are not diagnostic in most instances, given its unusual locations
- Histological findings along with immunohistochemical results are usually enough to reach a definite diagnosis
- By definition, the establishment of no direct connection to the CNS is required
- In ectopic meningiomas from other distant sites (for example, thoracic / mediastinum), metastasis from CNS needs to be ruled out before making this diagnosis (World J Surg Oncol 2012;10:17)
- Regarding the distinction between ectopic meningioma and meningothelial hamartoma / meningothelial proliferation, there are no definite criteria as of now; sometimes differentiating between these 2 entities can be very subjective and a bit arbitrary
Radiology description
- Given its rare occurrences at different uncommon locations, ectopic meningiomas are difficult to diagnose on radiologic imaging; however, exclusion of any direct connection of CNS is crucial in making a diagnosis
- Computed tomography (CT) imaging shows hyperdense or isodense signals with slight to heterogenous enhancement with contrast; compression deformation, hyperplasia and superficial bone resorption are commonly observed (J Oral Maxillofac Surg 2016;74:2216, Ear Nose Throat J 2022;101:NP383)
- In some cases, magnetic resonance imaging (MRI) is the preferred diagnostic imaging modality, with meningiomas being hypointense on T1 weighted images and hyperintense on T2 weighted images (J Oral Maxillofac Surg 2016;74:2216)
Radiology images
Images hosted on other servers:
CT findings
CT findings
MRI findings
Prognostic factors
- Like primary intracranial meningioma, tumor grade and extent of surgical resection are the most important prognostic factors for ectopic meningioma
- In general, ectopic meningioma of the head and neck tends to show a higher recurrence rate due to complex anatomy and difficulty in obtaining complete surgical resection (Ear Nose Throat J 2022;101:NP383)
- Rare instances of distant metastasis have been noted in few reported cases of anaplastic meningioma (J Neurosurg 2000;93:940, Head Neck Pathol 2009;3:116)
- Overall, prognosis is better than typical CNS meningioma (J Neurooncol 2011;102:81)
Case reports
- 19 year old man with meningothelial hamartoma of the scalp (Am J Dermatopathol 2022;44:602)
- Woman in her early 20s with primary extracranial meningioma of the pelvis (BMJ Case Rep 2023;16:e256988)
- 31 year old man with primary heterotopic meningioma of nasal cavity (Ear Nose Throat J 2022;101:NP383)
- 55 year old woman with primary ectopic meningioma in the thoracic cavity (Front Oncol 2023;13:1149627)
- 70 year old woman with ectopic thoracic meningioma (BMJ Case Rep 2021;14:e242020)
Treatment
- Given its propensity for local recurrence, complete surgical resection is recommended (Head Neck Pathol 2009;3:116)
- For cases in which complete resection is not possible due to complex anatomical location, radiotherapy and antiprogesterone treatment have been suggested by some studies; however, the efficacy of radiotherapy remains controversial (J Neurooncol 2011;102:81)
Gross description
- Usually 1 - 5 cm in size
- Tan-white, rubbery mass (Am J Dermatopathol 2022;44:e39)
- Overall, cellularity, collagen deposition and tumor grade affect the ultimate macroscopic appearance
- Ectopic pulmonary meningiomas show sharply marginated borders and are easily dissected from the surrounding lung; calcification and hemorrhage are seen (Front Oncol 2023;13:1149627, World J Surg Oncol 2012;10:17)
- Areas of necrosis in atypical and anaplastic cases can be seen
Gross images
Images hosted on other servers:
Solid pulmonary mass with bleeding and calcification
Pulmonary tumor with smooth surface
Frozen section description
- Identical to primary CNS meningioma (see primary CNS meningioma)
Microscopic (histologic) description
- Histologic features, including various morphologic variants, are identical to the intracranial counterpart
- Meningothelial meningioma, characterized by nests and lobules with meningothelial whorl formation, is by far the most common histologic type
- Psammomatous calcification is seen in a significant subset of ectopic meningiomas (Head Neck Pathol 2009;3:116)
- Meningothelial hamartomas are usually characterized by slit-like pseudovascular spaces reminiscent of lymphatics but lined by meningothelial cells
- Meningothelial nodules, with or without psammomatous calcification, can be seen (Am J Dermatopathol 2022;44:602)
Microscopic (histologic) images
Contributed by Rana Naous, M.D. and Azfar Neyaz, M.D.
Meningothelial meningioma
Meningothelial nodule in lung
Psammomatous calcification
Psammomatous calcification
Meningothelial meningioma (EMA)
Meningothelial meningioma (PR)
Meningothelial meningioma (SSTR2)
SSTR2
Cytology description
- Cytologic findings identical to primary intracranial meningioma (see primary CNS meningioma)
Cytology images
Images hosted on other servers:
Proliferation of spindle to round cells
Positive stains
- Vimentin
- EMA (variable intensity)
- SSTR2 (Acta Neuropathol 2015;130:441)
- Progesterone receptor (PR) (variable intensity)
Negative stains
- Cytokeratins are mostly negative (rare reports of cytokeratin positivity)
- Synaptophysin and chromogranin
- HMB45 and MelanA / MART1
- S100 mostly negative; some reported positivity
- p63 may be rarely expressed; tends to express in higher grade tumors
- CD34, STAT6 (Histol Histopathol 2022;37:1253)
Electron microscopy description
- Identifies numerous overlapping cytoplasmic processes, attached by prominent desmosomes and other intercellular junctions (Am J Surg Pathol 1996;20:492)
Molecular / cytogenetics description
- Similar to primary CNS meningioma, monosomy of chromosome 22 is seen in majority of ectopic meningiomas
Sample pathology report
- Scalp mass, excision:
- Ectopic meningioma (see comment)
- Comment: Microscopic examination reveals a relatively well circumscribed proliferation comprised of small clusters of bland, round to ovoid shaped meningothelial cells with interspersed pseudovascular spaces, hyalinization and psammomatous calcification. Immunohistochemistry is positive for EMA, SSTR2 and PR. Overall, the findings are compatible with ectopic meningioma.
Differential diagnosis
- Metastatic primary CNS meningioma or direct extension of primary intracranial meningioma:
- One of the most important factors to consider when dealing with ectopic meningiomas
- By definition, any intracranial connection would exclude the diagnosis of ectopic meningioma
- Depending upon meningioma morphology (meningothelial versus fibroblastic versus others), different diagnostic entities would enter into the differential diagnosis
- In addition, given a particular location, differential diagnosis varies greatly
- For example, ectopic meningioma arising from the head and neck needs to be differentiated from paraganglioma, schwannoma, melanoma, middle ear adenoma and metastatic carcinoma
- At lung / mediastinal location, the differential diagnosis includes sarcomatoid mesothelioma, solitary fibrous tumor, spindle cell thymoma, synovial sarcoma, amelanotic melanoma and sarcomatoid carcinoma
- Some common differential diagnoses
- Paraganglioma:
- Absent whorling
- Positive for neuroendocrine markers (synaptophysin and chromogranin)
- Cellular neurothekeoma:
- Positive for PGP9.5, CD63 (NKI / C3), neuron specific enolase (NSE) and MITF
- EMA, PR and SSTR2 negative
- Solitary fibrous tumor:
- Plexiform schwannoma:
- Perineurioma:
- Carcinoma, thymoma and mesothelioma:
- Positive cytokeratin markers
- Melanoma:
- Positive for melanocytic markers (HMB45, MelanA / MART1 and MITF)
- Well differentiated angiosarcoma:
- In the differential diagnosis for meningothelial hamartoma
- Positive for vascular markers (ERG, CD34 and CD31) (Am J Surg Pathol 1990;14:1)
- Paraganglioma:
Additional references
Practice question #1
Which of the following features is required by definition for the diagnosis of ectopic meningioma?
- Diffuse positivity of vimentin, EMA and PR immunostains
- Exclusion of any central nervous system (CNS) connection
- No evidence of cytologic atypia or any features of anaplasia
- Presence of prominent meningothelial whorl formation and psammomatous calcification
Practice answer #1
B. Exclusion of any central nervous system (CNS) connection. By definition, intracranial meningioma needs to be ruled out before making a diagnosis of ectopic meningioma. Answer A is incorrect because a diffuse positive result in these immunohistochemical stains is typically absent and not necessary for this diagnosis. Focal / weak staining of these IHC markers is often seen. Answer D is incorrect because although meningothelial whorls and psammomatous calcification are characteristic features of meningioma, their presence is not required for this diagnosis. Answer C is incorrect because atypical and anaplastic ectopic meningiomas have been reported in the literature and the presence of these features does not preclude ectopic meningioma.
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Reference: Ectopic meningioma
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Reference: Ectopic meningioma
