Abstract
Meningioma is a well-recognized tumour of the central nervous system. However, extracranial non-dural or ectopic meningiomas are rare and in most of the reported cases, meningiomas are diagnosed only after histopathologic examination. Over the last 5 years, the authors have seen three cases. In these case reports, they discuss the salient features of these lesions, which can aid the preoperative diagnosis and management of these patients. One of the cases is a rarity, owing to the extreme extracranial position which allowed the pressure of the tumour abrade the adjacent structures. In one case, reconstruction of the skull bone using polymeric materials (Acrylic matter) was necessary. In the other two cases, titanium plates and screws were used to reconstruct the jaw.
Meningioma is a common intracranial tumour with a variety of histomorphologic growth patterns, which are usually easily recognized . Their extracranial location is rare but two categories can be distinguished: primary and secondary extracranial meningiomas. The primary type arises from either displaced embryonic arachnoid cells or from multipotential mesenchymal cells, and the secondary type arises as a direct extension of an intracranial mass. Primary extracranial (ectopic, extracalvarial) meningiomas of the nasal cavity, temporal bone, paranasal sinuses, and nasopharynx (hereinafter referred to collectively as the sinonasal tract) are very rare.
The literature is generally limited to isolated case reports with a few reviews . Histologically, meningiomas of the sinonasal district are identical to their intracranial counterparts, although diagnostic difficulties are frequently encountered in the differential diagnosis with carcinoma, melanoma, and olfactory neuroblastoma resulting from the rarity of meningiomas in this location.
Meningiomas represent about 20–30% of all primitive encephalic tumours. They probably arise from the meningeal coverings, and arachnoidal cap cells of the brain and spinal cord and 1–2% have an extracranial location . Possible mechanisms for extracranial meningioma have been proposed .
The most frequent sites of an external mass are the orbit, the outer table and scalp, the paranasal sinuses, the nasal cavity, the parotid and parapharyngeal region. It has been estimated that about 20% of intracranial meningiomas could develop an extracranial extension, and the most common site is the orbit. Following invasion of the temporal bone, the most common extension route is through the jugular and lacerate foramina into the nasopharyngeal, retromaxillary, retromandibular and cervical spaces, whilst invasion of the external auditory canal is very uncommon . Extension through the foramina rotundum, spinosum and ovale, such as the pterygomaxillary fissure, the sphenopalatine foramen and the pterygopalatine canal is rare. When meningiomas occur in the head and neck, the diagnosis and management often represent a great challenge.
The differential diagnosis of extracranial meningiomas includes a variety of benign and malignant neoplasms, including epithelial tumours (carcinoma), neurogenic tumours (melanoma and olfactory neuroblastoma), vascular tumours (angiofibroma, paraganglioma), and mesenchymal tissue tumours (aggressive psammomatoid-ossifying fibroma) .
According to the WHO classification there are 15 histologic subtypes of meningiomas ( Table 1 ). Amongst these subtypes, meningothelial, fibrous and transitional (mixed) are the most common. The prognostic significance of these subtypes is very low, although some subtypes, such as clear cell meningiomas and papillary meningiomas, are clinically aggressive; 2–10% of these tumours are malignant.
| WHO grade | |
|---|---|
| Meningiomas with low risk of recurrence or aggressive growth | |
| Meningothelial | I |
| Fibrous (fibroblastic) | I |
| Transitional (mixed) | I |
| Psammomatous | I |
| Angiomatous | I |
| Microcystic | I |
| Secretory | I |
| Lymphoplasmacyte-rich | I |
| Metaplastic | I |
| Meningiomas with greater likelihood of recurrence and/or aggressive behaviour | |
| Atypical | II |
| Clear cell (intracranial) | II |
| Chordoid | II |
| Meningiomas of any subtype or grade with high proliferative index and/or brain invasion | |
| Rhabdoid | III |
| Papillary | III |
| Anaplastic (malignant) | III |
Meningiomas are soft, smooth-surfaced masses with a broad dural attachment; the microscopic findings show lobules of neoplastic cells creating a syncytial appearance, and fibrous tissue is typically scant. The cells show round to oval nuclei, delicate chromatin, small solitary nucleoli, and often nuclear-cytoplasmic invaginations called pseudoinclusions (syncytial variant). The transitional variant demonstrates prominent lobules, whorls, collagenized blood vessels, and psammoma bodies. The fibrous variant is generally less cellular and consists of elongated cells immerged in a collagen-rich matrix. The classic ultrastructural findings show interdigitating processes, well-formed desmosomes and hemidesmosomes. Atypical and malignant meningiomas demonstrate hypercellularity, necrosis, sheet-like growth and the cytologic findings include high nuclear-cytoplasmic ratios, coarse chromatin, prominent nucleoli, and high mitotic activity.
The clinical and radiographic features of these tumours are non-specific, and consequently an accurate diagnosis requires histologic evaluation. Histologically and immunophenotypically, extracranial meningiomas are the same as their intracranial counterparts. An awareness of these pathologic and immunohistochemical features should allow them to be distinguished from other sinonasal tract tumours. The clinical manifestations, radiographic findings, and histologic features cannot predict the clinical outcome accurately, even though, with complete surgical extirpation, sinonasal tract meningiomas have a good overall prognosis .
During the last 5 years, the authors have observed three cases of extracranial meningiomas. They discuss the salient features of these lesions, which can aid the preoperative diagnosis and management of these patients.
Case reports
Case 1
A 75-year-old female patient presented with progressive swelling over the right side of the outer head and temporal region. It was associated with local pain and progressive proptosis. She denied vertigo, imbalance or tinnitus. Her medical history was unremarkable. On examination, she had a 6 cm, firm, nontender, noncompressible swelling on the right temporal region, fixed to the underlying bone. The skin over the swelling was normal and the underlying mass could be pinched off ( Fig. 1 ). There were no other neurological symptoms or deficits. Neurologic examination, including evaluation of the cranial nerves, and head and neck examination were normal. Computed tomography (CT), before and after contrast administration, showed a large enhancing extracranial lesion located into the infratemporal fossa; the underlying bone was irregular and soft in places and it was infiltrated by the tumour ( Fig. 2 ).
An emicoronal skin incision was made on the right side ( Fig. 3 a ) and dissection revealed the tumour ( Fig. 3 b). The temporalis muscle was extensively infiltrated by the neoformation, so it was completely removed. The lesion was removed ( Fig. 3 c). It was also necessary to remove part of the temporal bone, which was partially destroyed by the tumour. This extremely rare presentation revealed a totally extracranial meningioma the pressure of which eroded the bone. Skull bone reconstruction was performed using polymeric materials (Acrylic) and fixed using titanium plates and screws. 3 weeks later, the Acrylic matter was removed due to an infection.
