CHONDROBLASTOMA OF THE PETROUS PORTION OF THE TEMPORAL BONE.
Chondroblastoma is an unusual benign tumor that occurs preferentially in long bones such as the tibia, humerus, and femur (11,16). Its origin may be also from pelvis, spine, ribs, and scapula and less commonly from calcaneus, patella and tarsal bones. It corresponds to less than 1% of all primary bone tumors (3, 4, 16) and it is found predominantly in the first 2 decades of life (1,10). So far the exact basic cellular phenotype remains unclear. While chondroblastomas have been long considered to derive from chondroblasts, these tumors might be reclassified as osteoid-forming neoplasm (1).
Cranial chondroblastomas are extremely rare and the first case was originally described by Denko and Krauel in 1955 (5). Chondroblastomas of the skull tend to occur in older patients. The average age for patients with temporal bone chondroblastomas is 53.6 years old (8). The most frequent location of the chondroblastomas involving the cranial bones is the squamous portion of the temporal bone and 30% to 50% of the lesions may present calcific foci (7). The extremely uncommon tumor location in the petrosal bone without squamosal involvement in the present case may be related to persistent cartilaginous centers of the chondrocranium (12). Swelling in the temporal region, plugged sensation in the ear and hearing loss are the most frequently reported complaints in cases of cranial chondroblastomas (15). In the present case, the lower cranial nerves deficit which presented as a transitory dysfunction during the first pregnancy and then evolved into a permanent deficit during the second gestation is an atypical clinical manifestation and may be related to the increase of the venous pressure during pregnancy.
Misinterpretation of the histology of chondroblastomas may occur because - as in the present case - the multinucleated giant cell containing stroma may be much more predominating than tumor components revealing the typical chondroid differentiation with chondroblasts and a chondroid matrix (2). Thus, its differential diagnosis includes in particular giant cell tumor. In contrast to chondroblastomas, giant cell tumors rarely show calcifications and do not contain areas with a chondroid matrix (6). In doubtful cases in which - different to the present case - unequivocal cartilaginous (chondroblastic) areas are not obvious, differential diagnosis of a giant cell tumor may be ruled out by S-100 immunoreactivity. Thereby, tumor cells in giant cell tumors do not express S-100, according to their histiocytic origin (9). In contrast, S-100 immunoreactivity is of no help in distinguishing chondroblastoma and cases of clear cell chondrosarcoma, a very rare subtype of chondrosarcomas (1,13,17). Different to chondroblastoma, clear cell chondrosarcoma affects mainly adults in the third to fifth decade of life, lacks eosinophilic cytoplasm of tumor cells and reveals less well defined cell borders (1).
Additionally, in clear cell chondrosarcoma only minor amounts of a chondroid matrix are intermingled (6). Furthermore, some cases of chondroblastoma are associated with a secondary aneurysmal bone cyst (6). Thus, tumor regions revealing typical aspects of an aneurismal bone cyst do not exclude chondroblastoma as underlying primary disease.
Wide resection should be attempted in treatment of chondroblastomas and radiation therapy should be reserved to recurrence or incomplete tumor removal, since sarcomatous degeneration has been reported after radiotherapy (14).
The authors thank Professor G. Delling (Division of Osteopathology, Institute of Pathology, University Hospital Eppendorf, Hamburg, Germany) for his reference diagnosis on the present case.
Contributed by Andrei Koerbel, M.D., Hubert Loewenheim, M.D., Rudi Beschorner, M.D., Florian Roser, M.D., Ulrike Ernemann, M.D., Richard Meyermann, M.D., Marcos Tatagiba, M.D.