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Clinical Problem Solving: Pathology
August 2002

Diagnosis Pathology Quiz Case

Author Affiliations
 

FREDERIC B.ASKINMDWILLIAM H. W.WESTRAMD

Arch Otolaryngol Head Neck Surg. 2002;128(8):976-977. doi:
Diagnosis: Middle ear meningioma

Meningiomas involving the middle ear are rare. When these lesions are found, they usually represent an extension from an intracranial tumor.1 However, a meningioma can arise as a primary neoplasm of the middle ear, where it is thought to originate from arachnoid cells trapped during embryonic development.2 An affected patient usually presents with tinnitus, hearing loss, headaches, and, frequently, extreme otalgia.3 Facial nerve palsy may result from involvement by the tumor.3 Computed tomography and magnetic imaging are often helpful in making the diagnosis. These tests help determine if the tumor in the middle ear represents a direct extension from an intracranial tumor.4

In a recent review of 20 cases of middle ear meningiomas, the average age of the patients was 45.3 years and 17 patients (85%) were female,3 consistent with other literature that found a strong female predilection.1 It is well documented that intracranial meningiomas occur most often in middle-aged women, exhibit an association with clinical obesity, and express receptors for female sex hormones.3,5,6 In one study, 30% of 330 intracranial meningiomas showed evidence of estrogen receptors, while 70% of 264 had progesterone receptors.5 However, there has not been agreement on the roles that obesity and hormone receptors play regarding the incidence and aggressiveness of meningiomas. The proposed theory is that obesity increases the metabolism of androstenedione to estrone, which would thus increase the amount of estrogen in circulation.6 This elevated level of estrogen could then exert its effects on hormone-responsive meningioma cells and induce proliferation.

Histologically, the cells of the middle ear meningioma are arranged in nests and whorls, producing the pattern characteristic of meningiomas in general. Most often, the cells have relatively uniform, oval nuclei and clear to faintly eosinophilic cytoplasm, with indistinct cytoplasmic borders. Mitotic figures are frequently absent. Psammoma bodies are often present. Immunoreactivity for EMA is a characteristic finding, while expression of S100 protein varies.

Other cellular, cytologically bland neoplasms that might be considered in the differential diagnosis of middle ear neoplasms include the jugulotympanic paraganglioma, middle ear adenoma, and low-grade adenocarcinoma of endolymphatic sac origin. The relatively common paraganglioma is composed of fairly uniform epithelioid cells that form aggregates bounded by delicate reticulin fibers. These structures, called Zellballen, are separated by the blood vessels of the characteristically rich vascular supply of this neoplasm. Some tumors may have large, cytologically bizarre cells interspersed among the dominant regular members of their constituent cells. Paragangliomas are usually immunoreactive for neuroendocrine markers and may also contain cells that are immunoreactive for S100 protein but do not express EMA.

The middle ear adenoma is a nonagressive neoplasm that consists of a multitude of small, intimately apposed nests and acinar structures lined by low columnar or cuboidal cells. These cells have eosinophilic cytoplasm and regular nuclei and often surround luminal secretions. The middle ear adenoma may express EMA, but its glandular light microscopic features distinguish it from a meningioma. Also, some middle ear adenomas express neuroendocrine antigens.7

There exists a more invasive and destructive, albeit still deceptively bland, epithelial middle ear neoplasm that has been designated by some authors as low grade adenocarcinoma of endolymphatic origin and by others as aggressive papillary middle ear tumor. The tumor cells are arranged in nests and complex papillations. They are cuboidal or low columnar, with eosinophilic cytoplasm and some nuclear variation, but lack mitotic activity. Although the neoplastic cells express EMA and S100 protein, they also possess cytokeratins and, occasionally, are positive for neuroendocrine antigens.8

Surgery is generally considered the treatment of choice for middle ear meningiomas. Furthermore, because of the tendency of the tumors to spread insidiously within the temporal bone and the intraoperative difficulty in distinguishing normal from involved tissue, an aggressive surgical approach has been advocated. Despite such treatment, these neoplasms are known to recur.1,3 Accordingly, follow-up computed tomographic scans are advisable, and yearly computed tomographic scans are often recommended for as many as 15 years after surgery.3

No doubt because of the rarity of middle ear meningioma, we found no studies devoted to those tumors that were considered cytologically malignant or that behaved in a malignant fashion. Studies of intracranial meningiomas have shown that tumors exhibiting mitotic activity along with nuclear pleomorphism and necrosis are more likely to behave in a pernicious fashion. Cytologic blandness, however, does not guarantee against recurrence.

The significance of expression of the proliferation antigen Ki67 (MIB-1) in intracranial meningiomas has been a matter of debate. Some authors have found an association between high proliferation indices and recurrence, while others have not.9,10

Our patient's clinical outcome, in fact, contrasts with the cytologic blandness of her tumor. She returned with right facial nerve palsy 4 months after surgery. She underwent additional surgical resection but continues to suffer right facial weakness. Pathologic examination of recurrent tumor revealed findings identical to those of the original tumor. Neoplastic cells were uniform and lacked nuclear atypia. No mitotic figures or necrotic foci were present. Expression of Ki-67 (MIB-1) proliferation antigen was again limited to fewer than 1% of the tumor cells. This case underscores the disparity between the innocuous microscopic appearance and the complicated clinical course that can be coexisting features of the middle ear meningioma.

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