Two Cases of Cartilaginous Choristoma—Not Chondroma of the Bony External Auditory Canal

Abstract

The presence of a cartilaginous mass on the bony external auditory canal is an unusual finding. Currently, two different diagnoses have been used to describe this type of mass: chondroma and cartilaginous choristoma. There is currently no consensus on which diagnosis is appropriate for this type of lesion. Choristoma is defined as a tumor-like growth of normal tissue occurring in an abnormal location. Histological examination alone cannot be used to distinguish between cartilaginous choristoma and chondroma, as both lesions comprise normal mature hyaline cartilage. To diagnose a mass as cartilaginous choristoma on the bony external auditory canal, it is necessary to confirm that it does not originate from the underlying periosteum. Here, we present the cases of two patients with typical cartilaginous masses on the bony external auditory canal, in which the surgical findings showed that the masses were not in contact with the underlying periosteum, indicating that cartilaginous choristoma—not chondroma—is an appropriate diagnosis for these mass lesions. The clinical findings (characteristic appearance and location) reported here may aid clinicians in the diagnostic and surgical management of these cartilaginous masses.

Cartilaginous Choristoma of the External Auditory Canal

“…[1][2][3] Furthermore, the incidental finding of such a mass in an anatomic site different from where one would normally expect to find the tissue in question solidifies the label of choristoma. [1][2][3] For choristomas of the EAC, a key differentiating factor is whether the mass originates from the underlying periosteum. 2 A chondroma would be histologically similar (both lesions have normal, nonneoplastic, hyaline cartilage), but it would be in direct contact with the bony portion of the EAC rather than the cartilaginous portion.…”

“…The new terminology characterizes the lesion better as a tumor-like growth with histologically normal tissue. [1][2][3] Furthermore, the incidental finding of such a mass in an anatomic site different from where one would normally expect to find the tissue in question solidifies the label of choristoma. [1][2][3] For choristomas of the EAC, a key differentiating factor is whether the mass originates from the underlying periosteum.…”

“…[1][2][3] For choristomas of the EAC, a key differentiating factor is whether the mass originates from the underlying periosteum. 2 A chondroma would be histologically similar (both lesions have normal, nonneoplastic, hyaline cartilage), but it would be in direct contact with the bony portion of the EAC rather than the cartilaginous portion. 2 Grossly, these lesions usually are small (1-2 mm), solitary, white, smooth, and firm.…”

“…1 Choristomas have been reported at other anatomic sites in the head and neck, notably epibulbar and intraoral. 2,4 In the ear, typically they are located at the medial portion of the anterior wall of the EAC. 3 The majority of cases have been diagnosed in the second, third, or fourth decade of life and the vast majority of reported cases occurred in Asians.…”

“…1 That being said, cartilaginous choristomas have little growth potential and there have been no cases of malignant transformation, suggesting that observation is a viable option. [1][2][3] There are multiple other lesions that can present similarly and should be included in the differential diagnosis of a solitary mass of the external auditory canal. Exostoses can be an incidental finding in the EAC.…”