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BENIGN CHONDROBLASTOMA OF THE TEMPORAL BONE STEPHEN G. HARNER, MD D. THANE R. CODY, MD, PhD

and DAVID C. DAHLIN, MD BY INVITATION

ROCHESTER, MINNESOTA

Benign chondroblastoma is a rare tumor in the temporal bone. It occurs preponderantly In middle-aged men as a mass in the posterosuperior region of the ear canal and is accom~nied by hearing loss. On pathologic examination, giant cells and focal regions of chondroid differentiation are noted. After the elltent of the tumor has been determined, the treatment Is surgical removal. Preoperative irradiation may be helpful. Long-term follow-up Is essential.

PRIMARY tumors of the cranial bones are considered rare, accounting for approximately 2% of all primary bone tumors. Bones of the cranial vault arise directly from primary connective tissue and do not have a cartilaginous phase, as long bones do. It is believed that many primary bone tumors originate as a result of a transition incident in the development of cartilaginous or endochondral bone.' Chondroblastomas are benign bone tumors. In 1942 the term "benign chondroblastoma" of the bone was first introduced, and the pathologic features were dellneated.t More than 400 chondroblastomas have been reported in the litera-

Submitted for publication Sept 12, 1976. From the Department of Otorhinolaryngology, Mayo Clinic, and the Mayo Foundation, Rochester, Minn. Presented at the 1978 Annual Meeting of the American Academy of Otolaryngology, liU Vegas, Sept 10-

13. Reprint requests to Mayo Clinic. 200 First St SW, Rochester, MN 55901 (Dr Harner).

ture through 1972; they account for less than 1% of all bone tumors.! There is a male-to-female preponderance of approximately 2 to 1. About 60% of the tumors have appeared in the second decade of life, but some have been found in older patients.

Chondroblastomas usually arise in the epiphyseal region of long bones. The most common initial complaint is pain. Radiographically, the lesions generally have well-defined areas of rarefaction, sometimes containing mineralized material and sometimes having a thin sclerotic rim of adjacent bone. The recommended treatment is total removal of the tumor and, when it is indicated, bone grafting." When en bloc excision is not feasible, curettage to normal bone has been effective. Radiation therapy has been used with some success, but it is not commonly employed, because of the fear of sarcomatous degeneration in later

years.! The actual number of chondroblastomas of the temporal bone (skull) that have been reported previously is not certain. The earliest report of such a tumor was by Denko and Krauel! in 1955. Another was reported by Cares and Terplan7 in 1971. In 1972 Dahlin and Ivins) reported on five cases of chondro biastoma of the temporal bone; one of the cases was from the Mayo Clinic and is included in this paper. This would account for seven cases documented in the

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world literature to date. In this paper, three cases are reviewed : the one mentioned previously by Dahlin and Ivins) and two new cases. A fourth case is briefly presented in the Addendum. An approach to the unique problems in the diagnosis and management of these tumors is also presented.

CASE REPORTS

CASE 1.-A 39-year-old man was first seen at the Mayo Clinic in March 1970. He complained of hearing loss in the right ear of four years' duration . He had some mild unsteadiness. On physical examination, the external auditory canal was 80% occluded by a skin-lined mass arising from the posterosuperior canal wall. Audiometric testing revealed a conductive hearing Joss of SS dB and 90% speech discrimination . Neurologic evaluat ion gave normal results. Tomograms of the temporal bone showed evidence of a tumor and severe destruction of the mastoid antral region on the right side, with extension into the middle ear cavity and through the tegmen tympani into the middle cranial fossa. The tumor also extended into the squamous part of the temporal bone (Fig 1). On April 2, 1970, exploration of the patient's right ear was performed. The tumor was found to be extremely vascular, friable, and gritty. An attempt was made to curet the bulk of the tumor; however, total removal was not possible . Permanent histologic sect ions showed evidence of benign chondroblastoma (Fig 2). No other therapy was offered at that time . Over the next year, the patient began having labyrinthine symptoms. On March 3, 1971, a mastoidectomy was performed. The masto id antrum and the ep itympanic space were filled with tumor, which was attached to the dura of the middle fossa. The horizontal semicircular canal was eroded, and no ossicles could be identified. All visible tumor was removed; because removal was known to be Incomplete, postoperative radiation therapy was given. The patient received 6,000 rads in 24 treatments. After the second procedure, hearing was lost. Follow-up through May 1978, seven years aher subtotal removal and radiation therapy, showed no evidence of recurrence.

CuI 2.-A 56-year-old man was first seen at the Mayo Clinic In July 1973. He complained of having had a "plugged" sensation in the leh ear over the past nine months. On examination, a mass wal detected in the postero-

Fig 1.-CllSe 1. A, Lytic defect in left temporal bone (arrows). B, Normal right temporal bone, for comparbon .

superior external auditory canal. Audiograms revealed a sensorineural hearing loss of 2S dB. Tomograms of the external auditory canal appeared normal. The biopsy specimen was interpreted as a ruptured epithelial cyst; Jater, the lesion could be recognized as a benign chondroblastoma (Fig 3). The patient returned in January 1974 and complained of decreased hearing on the left side aher an automobile accident. On examination, a skin-covered mass that arose in the posterior external auditory canal, obscuring the tympanic membrane, was disclosed . Results of aud lograms demonstrated a mixed hearing loss of 40 dB. On Dec 27, 1974, the mass was approached through a postauricular incision, and a gritty

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Fig 2.-Case 1. Specimen showing chondroblasts, ben ign giant cells, and calcifying chondroid island. Fibroblasts are present between islands of neoplastic cells (hematoxylin-eosin, X160).

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Fig 3.-Case 2. Biopsy specimen of external aud itory canal obtained In July 1973 show ing clusters of neoplast ic mononuclear cells and scatte red multinucleated cells. Prominent chondroid lobule dominates right half of figure (hematoxylin·eosin, X160).

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tumor was found . It was extremely vascular, and after enough tumor was removed for pathologic examination, the procedure was terminated. A study of the permanent sections led to a diagnosis of benign chondroblastoma. Tomograms revealed a destructive lesion in the region of the mastoid antrum (Fig4). Radiation treatment was prescribed, and a dose of 6,000 rads was given in 24 treatments. When the patient was seen three months later, he complained of vertigo, otalgia, headache, and de creased hearing. Tomograms showed that the destructive process had progressed.

performed on the patient, and study of the permanent pathologic sections resulted in a diagnosis of ben ign chondroblastoma. The patient was referred to us for definitive therapy. On physical exam ination, a skin-covered mass was detected, filling the posterosuperior external auditory canal and obscuring most of the tympanic membrane. An aud iogram showed evidence of a mixed hearing loss in the left ear and a mild sensorineural hear ing loss in the right ear. Roentgenograms showed a cystic lesion in the temporal squama, which also involved the floor of the middle cranial

Fig'4--Case 2. A, Tomogram of normal right ear . B, Destructive lesion In region of left mastoid antrum (arrows).

On May 13, 1975, the tumor was approached by means of modified radical masto idectomy, and all visible tumor was removed (Fig 5). The middle ear was intact. The dura of the middle and posterior fossae was widely exposed but kept intact . The tumor had become avascular after radiation therapy, and the surgical procedure was relatively simple. Follow-up through April 1978 indicated that the patient had not had any further problems. Hearing had returned to the same level as that of the normal ear.

CASE 3.-A 59-year-old man was initially seen at the Mayo Clinic on Dec 8, 1976. His first symptom was decreased hearing in the left ear, which began in September 1976. Hearing loss progressed, and the patient began having otalgia and tinnitus as well as some otorrhea and vertigo. On Nov 16, 1976, a biopsy was

fossa (Fig 6). Computed tomographic scans showed a mass (4x3 em) in the left temporal bone, without shift of the intracranial structures ; this suggested a primary bone tumor (Fig 7). The patient was given preoperative radiation therapy of 6,000 rads. A preoperative arteriogram showed the internal carotid artery to be free of tumor. On April 6, 1977, the mass was removed from the mastoid cavity, middle ear , and middle cranial fossa. This was accomplished as a joint procedure by an otologist and a neurosurgeon. The tumor extended medially toward the internal carotid artery, but did not involve it. The middle meningeal artery and the trigeminal ganglion were identified and left Intact. Substantial bleeding did not occur during the procedure, and removal of the tumor from the normal surrounding structures was relatively easy. The specimen cons isted of fragments aggregating to 4.5 cm in diameter (Fig 8). The patient had no postoperative difficulties and

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areas are calcified

Fig 7.-case 3. Computed tomographic scans made without and with injection of contrast material showIng lesion of left temporal bone. Flg6.-case 3. Lytic lesion in temporal bone (arrows).

returned to work in June 19n. No clinical or radiologic evidence of recurrence was apparent 14 months after the operat ion .

PATHOLOGIC ASPECTS The differential diagnosis of a benign tumor of the temporal bone that contains

giant cells should include cholesteatoma, reparative giant cell granuloma,a true giant cell tumor," aneurysmal bone cyst,'O benign chondroblastoma, and brown tumor of hyperparathyroidism." The reparative granuloma and the lesion of hyperparathyroidism may histologically be identical. Characteristically, the proliferating spindle cells produce recognizable col-

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Fig 8 .-eas~ 3. Tissue from mass showing cbondroblasts, a few benign multinucleated cells. and prominent pale-staining chondroid area (hematoxyltn-eosln, x 160).

lagen, which may be abundant in areas and, often, in condensing zones, merges into trabeculae of osteoid and bone. Such trabeculae, with proper orientation of the specimen, are often at or near the periphery of the tumor. If blood-filled spaces are sufficiently prominent, this lesion is designated an aneurysmal bone cyst. A giant cell tumor, which is rare in the bones of the skull, is made up of masses of similar mononuclear cells that do not produce intercellular matrixes. These lesions, of course, contain benign giant cells. An account of this defect is given by Hirschi and Katz.S

Benign chondroblastoma is similar to a giant cell tumor, but characteristically contains sheets of cells (sometimes with fairly distinct cell boundaries) that like those in true giant cell tumors, produce no collagen except in altered foci. The critical quality identifying benign chondroblastomas is the number of focal re-

gions with chondroid differentiation. The focal regions may be more subtle in chondroblastomas of the temporal bone than in those found In the more usual location in the end of a major tubular bone.

COMMENT Benign chondroblastoma of the temporal bone is a rare tumor. Three such tumors, the cases of which are presented in this report, occurred In men more than 38 years old . The patients had otologic symptoms initially, the first being hearing loss secondary to occlusion of the external auditory canal. In addition, the patients had otalgia and disequilibrium. On physical examination, a benign-appearing skin-covered mass arising from the posterosuperior external auditory canal was detected. Roentgenograms showed evidence of an osteolytic defect in the region of the mastoid antrum and of a slowly expanding destructive process. We have found that chondroblastomas may effectively be shown by the use of

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computed tomography with injection of contrast material (Fig 7).

obtained immediately after the operation and at yearly intervals.

In this clinical situation, the basic evaluation should include blood chemistry values, audiometric tests, vestibular testing, and tomography of the temporal bone. Other studies that may aid in diagnosis are computed tomography and arteriography, if intracranial extension is suspected. Tumors of the temporal bone are often much larger than the tomograms would suggest; therefore, the use of computed tomography in most cases is recommended.

Concern has been expressed that radiation therapy of these benign tumors may lead to malignant changes at some future time. Our series of 70 postradiation sarcomas of bone included one case in which sarcoma of the distal end of the femur developed nearly 30 years after radiation therapy for benign chondroblastoma of the upper end of the tibia. Steiner! also reported the occurrence of a sarcoma after radiation therapy for chondroblastoma. The overall probability of this happening appears so small that when compared with the alternatives, taking the risk is justified.

A histologic diagnosis must then be established. A transcanal or postauricular approach can be used. It may also be possible to establish a diagnosis by frozen section, but this has not been our experience. Because definitive treatment depends on the histologic diagnosis, a preliminary biopsy is appropriate.

If the tumor is small or avascular, it may be possible to proceed with definitive surgical treatment; that is, remove all the visible tumor by using curettage or similar means. The tumors, however, are usually extremely vascular and the tumor boundaries difficult to establish, resulting possibly in a grossly incomplete removal of the tumor. An alternative procedure of block resection of the temporal bone, as is performed for squamous cell carcinoma, is often too extensive for a benign tumor, and, therefore, preoperative irradiation is recommended. In the series presented, a dose of 6,000 rads was administered. Approximately six weeks after such radiation therapy, the tumor is removed by curettage. This may require the combined skills of a neurosurgeon and an otologic surgeon. At the time of the definitive procedure, the mass is easily removed to normal bone or dura without any attempt being made to include a margin of normal bone. Roentgenograms should be

CONCLUSIONS Benign chondroblastoma of the temporal bone is a rare tumor appearing predominantly in middle-aged men. In the series presented, it developed as a skin-covered mass arising in the posterosuperior external auditory canal. The recommended approach to the management of these tumors is to establish a histologic diagnosis and then to define the limits of the tumor by using tomography, arteriography, and computed tomography. The definitive therapy is surgical removal of the tumor. In some cases, preoperative irradiation may be a valuable adjunct. This is particularly true in larger tumors. Long-term follow-up is important.

ADDENDUM On Jan 29, 1979, a 57-year-old man came to the Mayo Clinic with a complaint of hearing loss and tinnitis in the left ear. On examination, there was total obstruction of the left external auditory canal. The audiogram showed a conductive hearing loss of 35 dB with 90% speech discrimination. Tomograms of the external ear canal showed a destructive lesion arising in the posterosuperior portion of the external auditory canal and extending

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into the mastoid air-cell system. Computed tomography with contrast gave normal results. A transfemoral arteriogram on March 14, 1979, revealed a tumor blush without evidence of intracranial extension. We suspected strongly that this might be a chondroblastoma. On March 15, 1979, we proceeded with an excisional biopsy. The tumor was isolated by performing a mastoidectomy and then a middle fossa craniotomy and was removed en bloc. Histologic examination showed typical benign chondroblastoma. The postoperative course has been without incident. Because we were able to remove the tumor completely, no radiation therapy is planned.

3. Dahlin DC, Ivins JC: Benign chondroblastoma: A study of 125 cases. Cancer 30:401-413, 1972. 4. Dahlin DC: Bone Tumors: General As-

pects and Data on 6,221 Cases, ed 3. Springfield, III, Charles C Thomas Publisher, 1978. 5. Steiner GC: Postradiation sarcoma of bone. Cancer 18:603-612, 1965.

6. Denko JV, Krauel LH: Benign chondroblastoma of bone: An unusual localization in temporal bone. Arch Pathol 59:710-711, 1955. 7. Cares HL, Terplan K: Chondroblastoma of the skull: Case report. J Neurosurg 35:614-618, 1971. 8. Hirschi S, Katz A: Giant cell reparative granuloma outside the jaw bone: Diagnostic criteria and review of the literature with the first case described in the temporal bone. Hum Pathol 5:171-181, 1974.

REFERENCES

9. Cares HL, Bakay L: Giant cell lesions of the skull. Acta Neurochir (Wien) 25:1-18, 1971.

1. Vandenberg HI Ir, Coley BL: Primary tumors of the cranial bones. Surg Gynecol Obstet 90:602-612, 1950.

10. Jeremiah BS: Aneurysmal bone cyst of the temporal bone. J Int Coli Surg 43:179-163, 1965.

2. Jaffe HL, Lichtenstein L: Benign chondroblastoma of bone: A reinterpretation of the socalled calcifying or chondromatous giant cell tumor. Am J Patho/18:969-991, 1942.

11. Raskin P, Rowe SN, Field IB: Hyperparathyroidism presenting as a giant-cell tumor of the middle cranial fossa. Ann Intern Med 69:301-304, 1968.

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