Giant mastoid osteoma with postoperative high-frequency sensorineural hearing loss.

Abstract

Osteomas occur throughout the temporal bone and, depending on their location, may cause tinnitus, hearing loss, vertigo, and facial nerve paresis. We present a rare case of a 25-year-old woman with a mastoid osteoma enlarging over a 6-month period. Other than a cosmetic deformity of her upper neck, the patient was asymptomatic. After surgical removal of the bony neoplasm, the patient was noted to have a high-frequency sensorineural hearing loss. This case study presents clinical, radiologic, intraoperative, pathologic, and audiometric findings of a mastoid osteoma and a review of the literature.

Introduction

Osteomas are bony tumors that rarely involve the mastoid portion of the temporal bone. On occasion these benign, expansive lesions require excision when causing a cosmetic deformity or pain. Resection requires meticulous drilling rather than excisional osteotomies, to avoid recurrence and damage to vital structures within the mastoid cavity. However, the otologic drill has been implicated in causing sensorineural hearing loss from both air- and boneconducted vibration and noise. This article describes a patient with an extensive mastoid osteoma who developed a postoperative sensorineural hearing loss after resection by otologic drill.

Case report

A 25-year-old woman was referred to the otology clinic for a mass over her left mastoid that had been slowly growing for the previous 6 months. Other than a cosmetic deformity of her upper neck, the patient was asymptomatic. She denied any hearing loss, tinnitus, vertigo, or pain, as well as prior

head trauma and otologic infections. Her history revealed no other medical problems.

The head and neck examination revealed a hard, immobile, nontender 3 x 3-cm mass extending from the left mastoid tip. The patient had a normally functioning facial nerve and no otologic abnormalities. Contrast-enhanced computed tomography (CT) of the neck showed a bony mass approximately 3.0 x 3.25 x 4.5 cm involving the inner and outer table of the mastoid (figure 1). A preoperative audiogram revealed normal hearing (figure 2).

The patient was taken to the operating room for surgical excision of the temporal bone mass. A postauricular mastoidectomy incision was made and extended inferiorly over the mass. The skin and soft tissue were raised and the periosteum incised. A dense, bony, broad-based mass involving the mastoid tip was found (figure 3). An air-powered otologic drill (Anspach Companies, Palm Beach Gardens, Fla.) was used to perform the mastoidectomy, allowing identification of the facial nerve. Drilling was performed between the border of the mass and mastoid cortex to further delineate its boundaries.

The bony mass was found adherent to the sigmoid sinus, stylomastoid foramen, fallopian canal, and digastric muscle. The bulk of the mass was removed en bloc. The remaining portion was drilled carefully away, and all tumor was grossly removed. There were no intraoperative complications. The patient received intravenous dexamethasone, with 8 mg given preoperatively and an additional 8 mg given at the end of the procedure.

Postoperatively the patient did well, without infection or facial nerve paresis. Histology revealed a mastoid osteoma of the compact type (figure 4). However, she did complain of left-sided tinnitus and hearing loss. We obtained an audiogram 3 weeks postoperatively that showed a left-sided, downward-sloping, high-frequency, moderate to severe sensorineural hearing loss from 2,000 to 8,000 Hz (figure 5). The speech reception thresholds and speech discrimination remained unchanged. A 7-month postoperative audiogram revealed persistent hearing loss. At 1-year follow-up, there is no recurrence of the mastoid osteoma.

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Discussion

Osteomas of the head and neck most commonly arise from the frontoethmoidal region. In the temporal bone they usually occur in the external auditory canal (EAC). Osteomas are true neoplasms thought to arise from preosseous connective tissue. Osteomas are rarely seen outside the EAC; however, they have been reported in almost every part of the temporal bone. A 1979 review of more than 50 extracanalicular osteomas showed that the mastoid was the most commonly reported temporal bone site, followed by the squama. (1)

Osteomas usually cause only a cosmetic deformity but, depending on their location, they may cause headaches, localized pain, hearing loss, vertigo, and tinnitus. The differential diagnosis of isolated temporal bone lesions includes eosinophilic granuloma, monostotic fibrous dysplasia, giant cell tumor, and solitary multiple myeloma. (2) A preliminary diagnosis is based on the patient's history and physical examination, supported by a CT scan.

Marlowe et al describe the Stuart histologic classification of osteomas. (2) Compact osteoma (also known as osteoma eburneum), as seen in our patient, is composed of dense lamellated bone and is the most common type of osteoma. Other types include osteoma cartilagineum, which has a cartilaginous covering, and osteoma cancellare, which is made of soft, spongy bone consisting of marrow; the latter is the rarest type.

Surgical excision of osteomas is commonly indicated when they are causing a cosmetic deformity or symptoms. Osteomas can encroach onto vital structures such as the facial nerve and sigmoid sinus, as in our case, and extreme care must be taken to avoid violating these structures dur ing resection. Marlowe suggests early removal of osteomas, while they are smaller and easier to excise completely, as well as to prevent encroachment onto vital structures and to prevent recurrence. (2)

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In our patient, the broad-based osteoma was adherent to the sigmoid sinus, fallopian canal, and stylomastoid foramen. Complete resection was achieved in our case, but complications should be considered when these structures are involved. Intracranial complications have been reported m association with removing osteomas from the sigmoid sinus. (3)

Middle ear surgery carries a small risk of sensorineural hearing loss. Causes of this iatrogenic hearing loss include (1) ossicular manipulation, causing trauma to the stapes footplate and direct trauma to the membranous labyrinth, and (2) noise from the otologic drill. One study demonstrated temporary sensorineural hearing loss due to auditory brainstem responses when guinea pigs were exposed to noise and simulated vibrations of an otologic drill. (4) Our case report implicates the otologic drill as the source of the hearing loss, since the ossicles were not directly manipulated and there was no direct trauma to the labyrinth.

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Acute or chronic acoustic trauma may cause high-frequency sensorineural hearing loss. Drilling intact skulls with cutting burs produces a noise level of up to 110 dB; this is louder than the noise levels diamond burs produce. (5) (OSHA regulations limit permissible noise exposure in the work environment to 0.5 hours per day when exposed to a sound pressure level of 110 dBA.) Factors determining cochlear damage are the intensity and duration of sound. (5) Moreover, the compact osteoma histologic type, which consists of dense bone, may require increased duration of drilling and may transmit more vibrational energy to the cochlea.

In our case, the sensorineural hearing loss persisted to postoperative month 7 and is probably permanent. Of note is the fact that dexamethasone did not protect the cochlea from the acoustic trauma caused by the otologic drill. This case required extensive drilling to remove a large and dense bony tumor. It is possible that limiting drilling time by only partially excising the tumor might have prevented the hearing loss. This may be reasonable if the tumor is near vital structures such as the facial nerve and sigmoid sinus; however, that approach carries the risk of residual tumor and continued growth onto these structures. Finally, future intraoperative auditory testing may be useful for monitoring threshold changes when extensive drilling is required.

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References

(1.) Denia A, Perez F, Canalis RR, Graham MD. Extracanalicular osteomas of the temporal bone. Arch Otolaryngol 1979; 105 (12): 706-9.

(2.) Marlowe H, Dave U, Wolfson RJ. Giant osteoma of the mastoid. Am J Otolaryngol 1980;1(2):191-3.

(3.) Gupta OP, Samant HC. Osteoma of the mastoid. Laryngoscope 1972;82(2):172-6.

(4.) Suits GW, Brummett RE, Nunley J. Effect of otologic drill noise on ABR thresholds in a guinea pig model. Otolaryngol Head Neck Surg 1993;109(4):660-7.

(5.) Kylen P, Stjernvall E, Arlinger S. Variables affecting the drill-generated noise levels in ear surgery. Acta Otolaryngol 1977;84(3-4):252-9.

From the Department of Otolaryngology-Head and Neck Surgery, University of Miami School of Medicine, Miami, Fla. Corresponding author: Thomas J. Balkany, MD, Department of Otolaryngology-Head and Neck Surgery, University of Miami, 1666 NW 10th Ave., #306, Miami, FL 33136. Phone: [phone]; fax: [phone]; e-mail: [e-mail]