Incidental discovery of a temporal bone chondroblastoma on an archived histopathological section

Chondroblastoma is a rare benign bone neoplasm (about 1% of all primary bone tumors) that predominantly occurs in the epiphysis of long bones of patients in their second and third decades. A craniofacial location accounts for only 6.6 to 7.1% of all chondroblastomas (1). More than 70 cases of temporal bone chondroblastomas have already been reported, all arising in older patients (50–60 year-olds) (2) and with a predilection for the petrous part of the temporal bone, most probably due to its endochondral origin.

Chondroblastoma exhibits typical features on computed tomography (CT) scan examination, and magnetic resonance imaging (MRI) observation demonstrates hypo intensity on T1-weighted sequences, with a variable intensity on T2-weighted images. Complementary examination, such as histological analysis, strengthens the diagnosis accuracy by revealing a well-defined neoplasm mostly composed of immature chondroid areas with focal calcifications and some multinucleated giant cells that may sometimes be confused with other giant cell lesions (3). When histologic diagnosis is challenging, several immunohistochemical tests can be used, such as Vimentin, Sox9, CD68 and KL1, but techniques using S100 protein reactivity gives the most consistent response (4).

Histopathological reports found in the literature were obtained from biopsies or surgical resection, but none were previously observed in a fully preserved temporal bone. Here, we report the first case, to our knowledge, of chondroblastoma observable in situ.

CASE REPORT

This 61-year-old woman presented a history of bilateral tinnitus associated with a progressive bilateral mixed hearing loss that was attributed to otosclerosis. She underwent bilateral stapes surgery, right ear at age 56 and left ear at age 58, with some improvement in hearing. She never reported any otalgia, otorrhea, temporomandibular joint symptoms or any central nervous system symptoms. Review of her medical history revealed a right parotid tumor removal in 1935 at age 34 (benign) and essential hypertension.

Histopathologically, on several successive sections, the left temporal bone shows a tumor non-refractive to polarized light, replacing bone in the midst of the inter-crural space of the posterior semicircular canal (Fig. 1). Analysis of the sections done by a Pathologist of St Vincent Medical Center (Los Angeles) revealed a well-defined lesion exhibiting mature and immature chondrocytes with areas of necrosis (Fig. 2). Since temporal bone processing requires a decalcification step, focal calcifications were not visible. Immnunohistochemical study of S-100 protein (mouse antibody, BioGenex, USA) was performed on the formalin-fixed, celloidin-embedded tissue, and positive reactivity was observed (Fig 2, inset).

Fig. 1.

The neoplasm (black triangle) seen in the midst of the posterior semi-circular canal arch is well-limited, with sharply defined edges. This section also shows an otosclerotic focus that is hugging the posterior semi-circular canal (empty star). (Hematoxylin & Eosin [H&E] X 20).

Fig. 2.

This chondroblastoma exhibits mature and immature chondrocytes (thin arrow, H&E X 100), with positive S100 nuclei immunostaining (inset, X400).

Otosclerotic lesions were observed in the peri carotid-cochlear area and the oval window area with stapedial involvement as well.

DISCUSSION

Contrary to the classical clinical symptoms (pain and swelling) observed in long bone tumors, temporal bone chondroblastomas are likely to induce hearing loss, tinnitus, balance disturbance, otorrhea, otalgia, and other neurological symptoms (3). In the present report, the otosclerotic lesions involving the stapes and the peri cochlear area most likely account for the hearing symptoms observed.

The location of this chondroblastoma, distant from the temporomandibular joint area contradicts the assumption made by some authors of a possible relation between these structures. According to others (5), embryonal cartilaginous rests entrapped within the tympanosquamous suture line of the temporal bone could be the origin from which chondroblastoma arise; however, our case does not corroborate this hypothesis. One theory we propose based on the particular location we report here is a possible relationship between chondroblastoma and the globulae interossei observed in temporal bones. Similar to cartilage rests entrapped within the tympanosquamous suture, the globulae interossei are comprised of cartilage-type tissue entrapped within the otic capsule bone.