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Benign osteoblastoma is an uncommon primary tumor of the bone. Any area of the skeleton may be affected by this tumor, but its occurrence in the temporal bone and middle ear is extremely rare. Clinical symptoms are nonspecific, even in the middle ear, and the diagnosis is often difficult in spite a complete physical and radiological examination. A biopsy is usually necessary for definitive diagnosis. Because of its potential for recurrence, local invasion, and, rarely, malignant transformation, a complete surgical excision remains the treatment of choice for osteoblastoma. We report a case of benign osteoblastoma involving the temporal bone and the middle ear and a review of the literature.
Osteoblastoma is a rare benign tumor of the bone, representing ~0.8 to 1% of all bone tumors.1,2 Although in 14 to 20% of cases this tumor affects the skull, its occurrence in the temporal bone and in the middle ear is extremely rare.2,3,4 We present a case of osteoblastoma in a young woman involving only the temporal bone and associated with tinnitus and progressive hearing loss.
A 26-year-old woman presented with a 6-month history of right pulsatile tinnitus and progressive hearing loss. She had no otalgia, otorrhea, otorrhagia, dizziness, or vertigo. In addition, no problem on the left ear was revealed. Her medical history was unremarkable except for a right hemithyroidectomy 3 years before and an antibiotic allergy. Clinical examination revealed a blush and swelling of the superior quadrants of the right tympanic membrane. The left ear and the facial function were normal. The Rinne test was negative in 256 and 512 Hz, and the Weber test showed lateralization to the right ear. The audiogram showed a 50 to 60 dB right conductive hearing loss.
Computed tomography of the right temporal bone showed a soft tissue lesion with areas of calcification located at the epitympanum and mesotympanum (Figs. 1 and and2).2). No osteolytic changes were appreciated.
The patient underwent a middle ear exploration that revealed a red and bloody mass occupying the whole middle ear. A biopsy of the lesion was taken that showed a tumor composed of woven bone spicules and trabecules with foci of osteoid and scattered osteoclast-type multinucleated giant cells. The intertrabeculae stroma was hypocellular and showed numerous capillaries and spindle cells (Fig. 3). Because of the lesion size and its location, a canal wall down mastoidectomy was performed with total excision of the lesion, followed by ossicular chain reconstruction with total ossicular reconstruction prosthesis. The postoperative facial nerve function was normal. Ten months after the surgery, the patient is asymptomatic, and hearing level has improved to 40 dB in the right ear.
Osteoblastoma, first described by Lichtenstein and Jaffe in 1956,5 is a rare primary tumor of the bone, representing ~0.8 to 1% of all bone tumors.2,3 Any area of the skeleton may be affected by osteoblastoma, but the most common sites of occurrence are the vertebral column and the long tubular bones of the lower extremities.4 Although in 14 to 20% of cases this tumor affects the skull, and lesions have been reported in the temporal, sphenoid, occipital, ethmoid, and frontal bones, its occurrence in the middle ear is extremely rare.2,3,4 Osteoblastoma has been described in all age groups, but it usually occurs in adolescents and young adults, with approximately 80% of patients younger than 35 years of age. It is more common in males (2:1).6,7,8
Clinical symptoms are nonspecific and include localized, insidious pain that is unresponsive to anti-inflammatory agents. Also seen are soft tissue swelling and erythema overlaying the tumor. When osteoblastoma affects the temporal bone and the middle ear structures, it may cause progressive hearing loss, usually conductive, and facial nerve compression, sometimes causing facial paralysis and facial pain.9,10 Because of the rarity of the lesion in this location, the diagnosis is often difficult despite a complete physical and radiological examination. A biopsy is usually necessary for a definitive diagnosis.6 Radiological imaging usually shows a well-defined osteolytic expanding lesion surrounded by a thin rim of new bone formation with evidence of varying degrees of calcification. Interestingly, the present case showed marked calcification areas but no evident lytic changes. The degree of ossification (i.e., calcification) has been related to the age of the lesion.8 Thus, younger lesions may be more radiolucent, with predominant osteoid areas and lytic changes, whereas older lesions may show higher calcification, predominant woven areas, and less lytic changes. Radiographic appearance of osteoblastoma is not specific and can be confused with fibrous dysplasia, ossifying fibroma, chondroblastoma, giant cell tumor, or aneurismal bone cyst.10 Computed tomography may show increased vascularity, which can be confirmed by arteriography. This last technique may be useful to exclude the possibility of a glomus tumor. Magnetic resonance imaging shows low and intermediate signal intensity on T1-weighted images and high signal on T2.7
Morphologically, osteoblastoma presents as a red-purple or gray tumor, well-circumscribed but nonencapsulated, with marked vascularity. Histologically, it exhibits a well-vascularized connective tissue stroma with irregular osteoid or woven bone rimmed by osteoblasts. The stroma shows numerous thin-walled capillaries and occasional extravasation of blood. Although multinucleated giant cells can be very numerous, mitotic figures are rare and atypia is usually absent.4,9
Osteoblastoma should be differentiated from osteoid osteoma and, more important, from osteosarcoma. The differential diagnosis also includes other benign lesions such as chondroblastoma, benign giant cell tumor, aneurysmal bone cysts, fibrous dysplasia, and their malignant counterparts.3,6 Clinically, osteoid osteoma is very similar to osteoblastoma, but it is more painful—usually causing nocturnal pain, which is relieved with salicylate therapy—and has no soft tissue mass. Both tumors are differentiated on the basis of the size: osteoid osteoma measures typically less than 1 cm, and osteoblastoma is larger.9 Radiologically, osteoid osteoma is less aggressive, shows predilection for the bony cortex, and is surrounded by more sclerotic bone. Histologically, the monotonous picture of osteoid osteoma contrasts with the great variety of osteoblastic and osteoclastic activities of osteoblastoma.4 It is most important to distinguish both of these benign lesions from osteosarcoma. This malignant bone tumor is more aggressive radiologically and histologically, is normally hypercellular with a higher mitotic activity, has areas of necrosis, and can produce malignant cartilage.3,8
Surgical excision remains the treatment of choice for osteoblastoma. Because of its benign nature, the conventional treatment of osteoblastoma has been local or intralesional curettage.5 However, an increasing number of authors have proposed complete resection of the tumor because: reported rates of recurrence after curettage are up to 16 to 20%1,5; histological differentiation between osteoblastoma and osteosarcoma sometimes may be difficult, especially with a small biopsy8; and osteoblastoma has potential for local invasion, aggressive growth, and, although extremely rare, malignant transformation, even several years after local excision.4,6
Radiotherapy and chemotherapy may be useful in some cases of recurrent, aggressive, or surgically unresectable osteoblastomas, usually located in vertebral column or extremities.7 However, numerous reports have demonstrated that radiation therapy may induce malignant transformation of a benign osteoblastoma.6,8