Fibrous dysplasia involving the skull base and temporal bone.

OBJECTIVE: To gain a broader appreciation of the clinical presentation, operative treatment, and outcome of patients with fibrous dysplasia involving the skull base. DESIGN: Retrospective review of a clinical case series. SETTING: A single tertiary academic medical center. PATIENTS: Twenty-one patients with histopathologically confirmed fibrous dysplasia involving the skull base cared for over a 15-year-period (1983-1998). MAIN OUTCOME MEASURES: Clinical and radiographic location of the fibrous dysplasia lesions within the skull base, clinical presentation, surgical intervention, and clinical outcome were tabulated for each patient. RESULTS: The ethmoids were most commonly involved (71%), followed by the sphenoid (43%), frontal (33%), maxilla (29%), temporal (24%), parietal (14%), and occipital (5%) bones. The most common presenting features included atypical facial pain and headache, complaints referable to the sinuses, proptosis and diplopia, hearing loss, and facial numbness. Surgical treatment, guided by clinical presentation, ranged from simple biopsy with conservative follow-up to craniofacial resection. CONCLUSIONS: Fibrous dysplasia can present in myriad ways within the skull base. Modern imaging modalities and histopathologic analysis have made diagnosis relatively straightforward. Surgery, particularly in such a challenging region as the skull base, should be reserved for patients with functional impairment or a cosmetic deformity. Because of the benign nature of the condition, the surgery itself should be relatively conservative, with the primary goal being preservation of existing function.

Dehiscence or thinning of bone overlying the superior semicircular canal in a temporal bone survey.

OBJECTIVE: To determine the incidence and etiology of dehiscences of bone overlying the superior semicircular canal in a temporal bone archive. DESIGN: A microscopic study was performed of 1000 temporal bones from 596 adults in a university hospital registry. Specimens were sectioned vertically in the plane of the superior semicircular canal. Measurements of minimum bone thickness over the superior canal were made in a subset of 108 randomly chosen specimens. All bones were examined for thinning or dehiscence relative to these norms. Clinical histories, when available, were reviewed. RESULTS: Complete dehiscence of the superior canal was identified in 5 specimens (0.5%), at the middle fossa floor (n = 1) and where the superior petrosal sinus was in contact with the canal (n = 4). In 14 other specimens (1.4%), the bone at the middle fossa floor (n = 8) or superior petrosal sinus (n = 6) was no thicker than 0.1 mm, significantly less than values measured in the control specimens (P<.001). Abnormalities were typically bilateral. Specimens from infants demonstrated uniformly thin bone over the superior canal in the middle fossa at birth, with gradual thickening until 3 years of age. CONCLUSIONS: Dehiscence of bone overlying the superior canal occurred in approximately 0.5% of temporal bone specimens (0.7% of individuals). In an additional 1.4% of specimens (1.3% of individuals), the bone was markedly thin (< or =0.1 mm), such that it might appear dehiscent even on ultra-high-resolution computed tomography of the temporal bone. Sites affected were in the middle fossa floor or a deep groove for the superior petrosal sinus, often bilaterally. These abnormalities may arise from failure of postnatal bone development. Thin areas of bone over the superior canal may be predisposed to disruption by trauma.

Relationship of the utriculus and sacculus to the stapes footplate: anatomic implications for sound-and/or pressure-induced otolith activation.

One hundred thirty human temporal bones that were sectioned in the vertical plane were examined to evaluate the relationship between the stapes footplate and the otolith organs. The shortest distance between the footplate and the utriculus was 0.58+/-0.10 mm in the posterior third of the oval window, 1.04+/-0.20 mm in the middle third, and 1.51+/-0.20 mm in the anterior third. The distance from the sacculus to the footplate was 1.33+/-0.20 mm in the middle third of the oval window and 1.31+/-0.18 mm in the anterior third. Membranous connections extending between the utriculus and the footplate were found in 26% of temporal bones. These membranous connections in coexistence with additional anatomic factors such as stapes hypermobility and/or dehiscence of bone within labyrinthine structures may predispose patients to sound- and/or pressure-induced otolith activation. The findings may have implications for different causes of the Tullio phenomenon.

Association of heterotopic neuroglial tissue with an arachnoid cyst in the internal auditory canal.

An arachnoid cyst arising within the internal auditory canal, or within the cerebellopontine angle and subsequently extending into the internal meatus and enlarging it, is a rare occurrence. Nevertheless, the neurootologist and the neurosurgeon have an interest in its existence because its clinical manifestations are identical with the ones produced by a schwannoma, involving overwhelmingly the cochleovestibular nerve in that region. An equally rare observation in that location is the presence of ectopic neuroglial tissue. The two can occur independently or in combination. Examples of such lesions are presented, and their possible pathogenesis is discussed.

Anatomic variations and anomalies involving the facial canal.

Congenital bony dehiscences in the facial canal result from incomplete closure during development and are observed in approximately 55% of temporal bones. Anomalies involving the facial canal frequently are encountered in malformations of the temporal bone. These anomalies include aberrations of the course of one or all of the segments of the canal; abnormal relation to the oval and round window; bifurcations and trifurcations of the nerve; and associations with dysplasia of the stapes, oval window, external ear canal, and auricle. Rarely, the facial nerve may be hypoplastic or totally absent. Two abnormal vessels occasionally may accompany the facial nerve in the Fallopian canal: a persistent stapedial artery and a persistent lateral capital vein.

Osteogenesis imperfecta of the temporal bone and its relation to otosclerosis.

Osteogenesis imperfecta (OI) designates a heterogeneous group of heritable disorders of connective tissue that in addition to bone may affect tendons, ligaments, fascia, skin, sclerae, blood vessels, teeth, and hearing. The current classification identifies at least four major syndrome groups or types. It also recognizes a considerable number of additional syndromes that may represent supplementary types or subgroups. Loss of hearing is the least constant of the prominent features of OI. Its incidence varies between 26% and 60%. In OI, formation and remodelling of bone are variously affected. In the temporal bone the development of the inner ear capsule may be involved severely. In the stapes the disturbance in lamellar bone formation can lead to extreme thinness, dehiscence, and nonunion of the stapedial superstructure with the footplate. Osteogenesis imperfecta can be associated with otosclerosis, another bone dysplasia with a different morphology. Otosclerosis, in turn, may interfere with sound conduction and perception. Thus, the hearing loss encountered in OI may be the result of OI, otosclerosis, or a combination of both.

Cephaloceles.

The meningoceles and encephaloceles of the calvaria and base of the skull are reviewed with regard to origin and local behavior. An additional variant is added to the subgroup of nasopharyngeal cephaloceles, the basioccipital nasopharyngeal cephalocele, which only recently has become recognized. The clinical importance, techniques for its identification, and surgical management are discussed with the aid of a case report.

Solitary (unicameral) cysts involving the temporal bone.

The primary unicameral cyst which involves the temporal bone is very rare. Only about 30 patients have been reported in the literature during the past ten decades. The lesion is most frequently encountered in the first and second decade of life. In contrast to the other locations in the skeleton, it usually remains asymptomatic for a long time until it causes a deformity or dysfunction. The etiology has so far remained obscure. Its occasional association with malformations of the ears and nasopharynx and other developmental anomalies, its incidental bilateral occurrence, and certain histological aspects may suggest a congenital origin or a localized defect in bone formation and remodeling.

Sclerosteosis involving the temporal bone: histopathologic aspects.

Sclerosteosis is a rare, potentially lethal, autosomal recessive, progressive craniotubular sclerosing bone dysplasia with characteristic facial and skeletal features. The temporal bone changes include a marked increase in overall size, extensive sclerosis, narrowing of the external auditory canal, and severe constriction of the internal auditory meatus, fallopian canal, eustachian tube, and middle ear cleft. Attenuation of the bony canals of the 9th, 10th, and 11th cranial nerves, reduction in size of the internal carotid artery, and severe obliteration of the sigmoid sinus and jugular bulb also occur. Loss of hearing, generally bilateral, is a frequent symptom. It often manifests in early childhood and initially is expressed as sound conduction impairment. Later, a sensorineural hearing loss and loss of vestibular nerve function often develop. Impairment of facial nerve function is another feature occasionally present at birth. In the beginning, a unilateral intermittent facial weakness may occur which eventually progresses to a bilateral permanent facial paresis. The histologic examination of the temporal bones from a patient with sclerosteosis explains the mechanisms involved in the progressive impairment of sound conduction and loss of cochlear, vestibular, and facial nerve function. There is a decrease of the arterial blood supply to the brain and an obstruction of the venous drainage from it. The histopathology reveals the obstacles to decompression of the middle ear cleft, ossicular chain, internal auditory and facial canals, and the risks, and in many instances the contraindications, to such procedures. On the other hand, decompression of the sigmoid sinus and jugular bulb should be considered as an additional life-saving procedure in conjunction with the prophylactic craniotomy recommended in all adult patients.

The jugular bulb in otologic surgery: anatomic, clinical, and surgical considerations.

The jugular bulb varies widely in position and dimensions. In certain pathologic conditions there is an increased incidence of jugular bulb enlargement, but such enlargement also occurs without an obvious underlying cause. Jugular bulb enlargment may lead to clinical symptoms for the patient and particular difficulties for the otologic surgeon, not only in the middle ear but also in neurotologic approaches. The different clinical aspects and problems associated with jugular bulb enlargement are discussed with illustrative cases and temporal bone histologic findings.

Acoustic neurinomas.

Eight nerve tumors account for about 8 to 10% of all intracranial tumors, and for about 71 to 75% of all cerebello-pontine angle tumors. They occur particularly in the middle decades of life and are twice as frequent in females as in males. They originate from the distal neurolemmal portion of the nerve, in most instances, from the vestibular division, and represent a neoplasia of the cells of Schwann. Two prominent types of tissue "A" and "B" of Antoni can be distinguished histologically. Regressive changes are frequent and lend them a colorful appearance. Bilateral eighth nerve tumors occur in about 4%. These tumors reveal certain characteristic differences. The differential diagnosis must include: meningiomas, epidermoids and gliomas, as well as a number of other space-occupying lesions.

Fibrous dysplasia of the temporal bone. Update with case reports.

Fibrous dysplasia is a fairly common, well demarcated, misdifferentiation of the bone-forming mesenchyme affecting a single, several, or many bones, in which skeletal changes are the salient feature, but in which certain endocrinopathies, abnormal pigmentation of skin and mucous membranes, and occasionally other abnormalities form part of the entire disease process. The clinical and pathological aspects of the disease and its involvement with the temporal bone have been previously discussed. Two recent case histories are added here.

Neurinomas of the trigeminal nerve.

Trigeminal neurinomas account for about 0.2 per cent of all intracranial tumors and for about 2 to 3 per cent of all intracranial neurinomas. Trigeminal neurinomas occur most frequently in persons in the middle decades of life, with the highest incidence between the ages of 38 and 40 years. They show no sex predilection. Although very rare, trigeminal neurinomas are of considerable interest to the neurotologist because of their relation to the temporal bone, skull base, sphenoid and maxillary sinuses, nasopharynx, infratemporal fossa, and, in rare instances, the oral cavity. In addition to producing disturbances of fifth nerve sensory and motor function, these tumors are often associated with other symptoms, such as occlusion of the eustachian tube (sensation of fullness and conductive hearing loss), otalgia, exophthalmos, paralysis of the third, fourth, and sixth cranial nerves, and signs of posterior fossa involvement (sensorineural hearing loss, tinnitus, cerebellar ataxia, and involvement of cranial nerves VII and IX through XI), any of which may be the initial clinical manifestation of the neurinoma. Symptoms depend on the site of origin and course of development. Bilateral trigeminal neurinomas are a manifestation of the central form of neurofibromatosis.

Meningiomas invading the temporal bone with extension to the neck.

Meningiomas are the second largest group of brain tumors after gliomas. They account for 13 to 18 per cent of all primary intracranial neoplasms. The majority occur in the cerebral chamber; only 8 to 9 per cent are located in the cerebellar chamber. Meningiomas are hamartomatous, not truly neoplastic tumors, which arise from dural fibroblasts and particularly from arachnoid cells that tend to cluster around the tips of the arachnoid villi. Their preferential sites correspond closely with the locations where arachnoid villi are most frequently encountered, namely, along the major venous sinuses and their contributory veins, at the foramina of exit of the cranial nerves, and where arachnoid cell clusters are found within the trunk or the perineural sheaths of cranial nerves within or adjacent to the basal foramina. Of all intracranial meningiomas, 20 per cent eventually develop an extracranial extension. These extracranial extensions project, in order of decreasing frequency, to 1) the orbit, 2) the external table of the calvaria, 3) the nasal cavity and paranasal sinuses, and 4) the parapharyngeal (cervical) space. Once a meningioma has gained access to the temporal bone, its tendency to extend beyond the confinements of the skull increases to 43 per cent. The most frequent pathway is through the jugular and lacerate foramina into the parapharyngeal space, where it may manifest as a nasopharyngeal, oropharyngeal, retromaxillary, retromandibular, or cervical neck mass. A meningioma in the parapharyngeal area can represent 1) an extracranial extension of a primary intracranial tumor, 2) a neoplasm arising in the jugular foramen, 3) a neoplasm originating from an arachnoid cell cluster within the trunk of a cranial nerve or its perineural sheaths within or near a neural foramen, or 4) a metastasis to a cervical lymph node from a primary intracranial meningioma. Meningiomas extending to the neck are unique because of their tendency toward extracranial expansion, higher incidence of local recurrence, multicentric growth, and frequent combination with other neoplasms of the central nervous system. They are frequently an expression of the central form of neurofibromatosis (von Recklinghausen's disease).

Sclerosteosis involving the temporal bone: clinical and radiologic aspects.

Sclerosteosis is one of the rare, potentially lethal, autosomal recessive, progressive, craniotubular sclerosing bone dysplasias. Syndactyly of the second and third or other fingers is evident at birth. Hyperostosis and sclerosis are most prominent in the skull and tubular bones, and are frequently associated with excessive height and weight. The typical facial deformity is apparent by the age of 5 years. The changes involving the temporal bone include a marked increase in overall dimensions, extreme sclerosis, and narrowing and constriction of the external ear canal, middle ear cleft, internal acoustic meatus, and falloppian canal. Impairment of hearing, as a rule bilateral, is a frequent presenting symptom which may manifest in early childhood. Initially it is an expression of interference with sound conduction; later it may become associated with a loss of sound perception. Impairment of facial nerve function is another salient feature which occasionally is present at birth. As a rule, it manifests initially as a unilateral, recurrent paresis, eventually progressing to a bilateral permanent partial loss of facial nerve function. Since impairments of hearing and facial nerve function are two of the salient features, present at birth or in early childhood, the responsibility for recognizing the disease often falls upon the otolaryngologist. The clinical and radiologic features permit not only early recognition of the disorder but also differentiation from similar bony dysplasias. Hyperosteosis and sclerosis of the skull lead to thickening and distortion of the calvaria, cranial base, and foramen magnum resulting in reduction of the intracranial volume, interference with the cerebral blood flow, resorption of cerebrospinal fluid, and gradual increase of intracranial pressure. Severe headaches resulting from this mechanism often develop in early adulthood, and several patients have died suddenly from impaction of the medulla oblongata in the foramen magnum. Decompression of the transverse sigmoid sinus and jugular bulb may be lifesaving, combined with a posterior, and if necessary, an anterior, craniectomy for decompression. Early decompression of the internal acoustic meatus and falloppian canal may help in the preservation of cochlear and facial nerve function.

A new, treatable source of recurrent meningitis: basioccipital meningocele.

A 19-month-old boy suffered eight episodes of bacterial meningitis. During the ninth episode a meningocele of the basioccipital clivus communicating with the nasopharynx was discovered. Identification of the organism causing the episodes of meningitis was not helpful in pointing to the site of this congenital anatomic defect. Surgical closure of the defect has prevented further recurrences.

The facial canal: normal anatomy, variations and anomalies. I. Normal anatomy of the facial canal.

Modern otologic surgery revolves around the use of the operating microscope. The surgeon must have a thorough knowledge of all structures in the temporal bone, particularly since surgery may now be directed to areas in its deeper portions. Of concern here is the whereabouts of the facial canal in its complex course through the temporal bone. A detailed descriptive anatomy with emphasis on the relations of the facial canal to adjacent structures is presented. The variations in the course of the facial canal are discussed. The location of dehiscences in the bony canal wall are described. Finally, great stress is laid upon presentation of these anomalies known to us which can occur in the course of the facial nerve through the temporal bone. These anomalies have clinical and surgical significance.

Fibrous dysplasia: a review of the disease and its manifestations in the temporal bone.

Fibrous dysplasia is a fairly common, localized misdifferentiation of the bone-forming mesenchyme affecting a single or many bones, in which skeletal aberrations represent the cardinal feature, but in which certain endocrinopathies, abnormal pigmentation of skin and mucous membrane, and occasionally other abnormalities form part of the entire disease process. The craniofacial skeleton is one of its predilective sites and therefore the temporal bone may become involved. In such instances the disease manifests itself with 1) progressive loss of hearing, 2) increasing obliteration of the external ear canal, and 3) enlargement and distortion of the temporal bone. The first part of this communication is concerned with a review of the clinical and pathological aspects of the disease in general. The second part is concerned with a discussion of the clinical manifestations in the temporal bone, based upon analysis of the entire literature and the authors' personal experience. The indications for surgical intervention include 1) maintenance of a normal outer ear canal, 2) preservation of cochlear and vestibular function, and 3) prevention of secondary complications.