Introduction

Meningiomas of the temporal bone are rare. Chang et al found case reports of only 77 patients from 1886 to 1998.1 However, the temporal bone is an important anatomical pathway for approaching meningiomas. This chapter concentrates on tumors that arise primarily within the confines of the temporal bone, including the internal auditory canal (IAC) and jugular foramen. Discussions of tumor within the cerebellopontine angle and petroclival region are found in Chapters 28 and 29.

Anatomy

The disarticulated temporal bone is a roughly pyramidal shape. In the lateral direction, its broad base is formed by the squamosal, tympanic, and mastoid portions of the temporal bone. Medially, the bone tapers into the petrous apex, including the region of the IAC. The superior surface of the temporal bone is the middle cranial fossa, containing the greater superficial petrosal nerve and arcuate eminence. This bony plate is the tegmen of the mastoid and middle ear cavities. The posterior surface is the cerebellar plate, and its most important structure is the sigmoid sinus. Anteriorly, the temporal bone articulates with the condyle of the mandible and is in continuity with the sphenoid bone. Inferiorly, the temporal bone gives off the jugular vein, the facial nerve, and the lower cranial nerves (IX, X, and XI) and receives the internal carotid artery. A thin plate of bone, the carotid crest, separates the carotid artery from the jugular bulb. Anatomical studies have shown that the anterior, or pars nervosa, portion of the foramen contains the inferior petrosal sinus and the glossopharyngeal nerve.2–4 An intimate understanding of these relations is required to comprehend the surgical approaches in the temporal bone.

Sites of Involvement

Meningiomas have been described involving all portions of the temporal bone. The middle ear, eustachian tube, IAC, and jugular foramen are the four most common locations of meningiomas in the temporal bone.5 Thompson et al described a series of 36 tumors from a pathology database.15 Their series included a majority of middle ear only tumors (25), followed by ear canal only (four), temporal bone only (two), or a combination of sites (five). Their series did not include jugular foramen tumors. Rarely, meningiomas have been described occurring in the geniculate ganglion6,7 and along the intratemporal facial nerve.8

Nager has divided temporal bone meningiomas into tumors that are an extension of an intracranial tumor (type 1) and those that are not (type 2),9 but this terminology can be confusing. Therefore, these tumors have also been characterized as primary, meaning site of origin within the temporal bone, or secondary, meaning site of origin outside the temporal bone, but with extension into it. The secondary tumors are much more common.

Primary temporal bone tumors have their origin from a nest of ectopic, extracranial arachnoid villi cells.1 Secondary tumors can extend into the middle ear through one of four pathways: the tegmen tympani, the posterior fossa plate, the IAC, or the jugular foramen.

Meningiomas of the jugular foramen can occur either as a primary tumor or as secondary extension from an intracranial location (cerebellopontine angle or petroclivus).10 Primary jugular foramen meningiomas can extend superiorly into the middle and inner ear, medi-ally into the cerebellopontine angle, or inferiorly into the neck.

Incidence and Frequency

Meningiomas are the second largest group of brain tumors after gliomas, accounting for 15 to 18% of all intracranial tumors.11 Only ~2% of meningiomas are found within the temporal bone.10,12,13 In a series of posterior fossa meningiomas, Roberti et al reported that of 161 consecutive cases in 6 years only seven (4.3%) involved the jugular foramen.13 Several case series, usually no more than 40 cases, have been reported in the literature since 1990 ( Table 30.1 ). Of tumors limited to the temporal bone, the jugular foramen is the most common site. IAC meningiomas are exceedingly rare, with only 14 tumors reported in the literature.14

The majority of patients are women. The mean age at diagnosis is roughly 45 to 50 years.15 The exception to this rule is meningiomas at the geniculate ganglion, which seem to present in younger patients and perhaps come to earlier diagnosis because of progressive facial paralysis.

Pathological Features

Meningiomas arise from arachnoid villi, which can be found in the jugular foramen, middle fossa, or IAC.2 Arachnoid villi are also found throughout the temporal bone.16 Nager has described arachnoid extensions along the nerve sheaths of the greater superficial petrosal nerve and cranial nerves VII through XII.9 Arachnoid villi are numerous around dural sinuses, explaining the occurrence around the jugular bulb.

Psammoma bodies are spherical, laminar, calcified structures that are frequently associated with meningiomas.17 However, psammoma bodies are also found in normal temporal bones, without an associated meningioma. The occurrence of psammoma bodies within the IAC, along the facial nerve, geniculate ganglion, and posterior ampullary nerve may be a normal consequence of aging.17

Pathologically, temporal bone meningiomas are frequently of the syncytial (meningothelial) variety.5,10,15 A few secretory meningiomas have been found in the middle ear and produce symptoms similar to chronic otitis media.18–20 Immunohistochemically, most temporal bone meningiomas are positive for vimentin and epithelial membrane antigen (EMA).15 A minority of these tumors are positive for S-100 or cytokeratin or both.5

Although these tumors are classified as benign, the characteristics of local recurrence, invasion of bone and nerves, and radioresistance make treatment treacherous.

Mitotic activity, brain invasion, micronecrosis, nucleolar pleomorphism, nucleolar prominence, and increased cellularity are all linked to a diagnosis of atypical or malignant meningioma.21

Symptoms and Signs

The symptoms and signs of temporal bone meningiomas are nonspecific. The symptoms are common for any otic process: hearing loss, middle ear effusion or mass, external ear swelling or mass, otalgia, or otorrhea ( Fig. 30.1A ).15,22 In a relatively large series of 56 patients, Arriaga et al reported hearing loss in 85%, dizziness in 61%, tinnitus in 75%, headaches in 32%, and cerebellar findings in 23%.11 A middle ear mass was found in four of 13 (30.7%) patients with jugular foramen meningiomas.10 Primary temporal bone meningiomas have also been described as presenting with signs of chronic otitis media with perforation19,23 or serous otitis media24 ( Fig. 30.2A ). Because these symptoms are largely nonspecific to a pathological diagnosis, biopsy might be necessary for confirmation. External ear canal masses are readily biopsied in the out-patient clinic, most without needing local anesthetic.

Facial weakness or paralysis and lower cranial nerve dys-function are seen in patients with temporal bone meningiomas. Facial nerve dysfunction can be subtle and might be manifest only by a delayed blink or twitching in an isolated branch. Careful, directed inspection of facial function is required to detect this mild dysfunction ( Fig. 30.3 ).

Tumors that involve the jugular bulb have the potential to involve the lower cranial nerves. The hallmarks of dysfunction in these nerves are a weak, breathy, or wet-sounding voice and dysphagia or aspiration. Careful evaluation of these nerves with fiberoptic nasopharyngoscopy is required. When vocal fold dysfunction or dysphagia is found, the patient should be referred to a speech pathologist for evaluation utilizing laryngeal videostroboscopy and modified barium swallow.

Auditory and Vestibular Evaluation

Patients with complaints of hearing loss are always evaluated by routine audiometry, including pure-tone testing, speech audiometry, and middle ear immittance (tympanometry). This test clearly defines the level and type of hearing loss: conductive ( Fig. 30.2B ), sensorineural ( Fig. 30.4A ) or mixed ( Fig. 30.5A ). This test is an essential first step in evaluating temporal bone meningiomas. The nature and degree of hearing loss at presentation have important implications for the approach taken for disease removal. The level of speech understanding (also called speech discrimination score [SDS]) and the pure tone threshold identify patients with useful or serviceable hearing versus those with measurable or nonserviceable hearing. A consistent rule for serviceable hearing is an SDS greater than 50% and a pure tone threshold less than 50 dB. Conductive hearing loss occurs with tumors that have a middle ear component. Tumors that erode into the middle and inner ear produce a mixed hearing loss. Hearing loss may be either sudden or progressive.16,25 Pensak et al documented hearing loss in 6/15 patients (40%).26 The implication is that perhaps 60% of patients will have normal hearing ( Fig. 30.6A ).

Auditory brain stem response (ABR) is an important test to measure the function of the auditory nerve and brain stem pathways. This test has important implications for tumors that are in the cerebellopontine angle, but it might not provide clinically useful information for tumors that are within the temporal bone. Arriaga et al reported normal ABR in 37% of their patients.11 Pensak et al reported abnormal ABR in 5/14 patients (35.7%).26

Vestibular testing, such as electronystagmography (ENG), vestibular evoked myogenic potentials (VEMP), rotary chair test, and computerized dynamic posturography (CDP), can provide information on the function of the vestibular organs. These tests should be performed in patients who present with vertigo or symptoms of vestibular dysfunction. Arriaga et al reported that ENG was abnormal in 87% of their patients ( Figs. 30.2C and 30.5B ).11 However, these tests have not been used on a consistent and widespread basis and thus are not considered essential elements of the evaluation.