Osseous/Cartilaginous Choristoma

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Clinical Features

Submucosal cartilage is not encapsulated and shows no dysplasia.






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Extraskeletal proliferation of bone and cartilage in oral and maxillofacial soft tissues probably reflects the multipotential nature of primitive mesenchymal cells throughout the region. Usually developmental in origin, some of these proliferations seem to occur as a result of local trauma. Several terms are used for them.

Choristoma (aberrant rest, heterotopic tissue) is defined as an histologically normal tissue proliferation or nodule of a tissue type not normally found in the anatomic site of proliferation. Hamartoma is defined as a benign tumor-like nodule composed of an overgrowth of mature cells and tissues that are normally found in the affected part, but with disorganization and often with one element predominating. The occurrence of multiple hamartomas in the same patient is called hamartomatosis. It is possible that some or many examples of osseous choristoma are nothing more than old cases of heterotopic ossification, but the two lesions have traditionally been classified as separate and distinct entities. Likewise, the presence of ectopic tissue elements from more than one germ cell layer has traditionally been called teratoma (see elsewhere in this book), and it is not unusual for an oral or cervicofacial teratoma to contain bone or cartilage.

Clinical Features

Osseous/cartilaginous choristoma is characteristically seen as a painless, firm nodule in young adults, especially in females, and has most frequently been reported on the tongue, although no submucosal site is immune (Figures 1 & 2). It seldom reaches a size greater than 1.5 cm., although even small lesions may produce local dysfunction if located on the lateral border of the tongue. A similar lesion, osteoma cutis, is found beneath the skin of the face and other areas, but is usually considered to be a different entity.

A unique cartilage-producing form of this tissue-level disorder is found on the edentulous alveolar ridge of a denture wearer, especially in the anterior maxilla. Presumably trauma-induced, this self-limiting Cutright tumor (chondroid choristoma, traumatic osseous and chondromatous metaplasia) may produce pressure atrophy of underlying bone, may become tender, and may contain bone in addition to cartilage (Figure 3).  Another chondroid choristoma, mistakenly termed chondroid hamartoma is frequently found in the anterior tongue of individuals with the orofaciodigital (OFD) syndrome, type I.

When multiple primary cutaneous ossification is encountered, it may be part of Albright’s hereditary osteodystrophy, which is associated with congenital or early subcutaneous ossifications of the extremities, trunk and scalp. Oral mucosal involvement is very rare. The bony spicules in this disease may produce surface ulceration or may extrude from the surface. Pseudohypoparathyroidism and pseudopseudohypoparathyroidism are frequently observed in this condition, which is inherited as an X-linked or autosomal dominant trait.

Pathology and Differential Diagnosis

The osseous/cartilaginous choristoma is comprised of a submucosal proliferation of benign and normal (perhaps immature) bone or cartilage (Figures 4-6). These "abnormal" tissues are embedded within a background stroma of fibrovascular connective tissue, usually without true encapsulation but often with a pseudoencapsulation. Cartilage may be active and mimic synovial chondromatosis (joint mice) or soft tissue chondroma.  Bone maturation often results in lamellar bone, perhaps with hematopoietic or fatty marrow (Figure 7). Choristomas and hamartomas given other specific diagnostic names, such as Fordyce granules (ectopic sebaceous glands) and oral tonsils (benign lymphoid aggregates) are discussed under those names in the present text.

Osseous choristoma may be confused with heterotopic ossification (myositis ossificans), but the latter is typically located in muscle and has more osteoblastic activity than the choristoma. Differentiation of osseous choristoma from peripheral ossifying fibroma is not usually difficult because the latter has a unique cellular stroma of oval, primitive mesenchymal cells and is found exclusively on alveolar bone surfaces. Neither cartilage nor marrow is produced by the peripheral ossifying fibroma and, by tradition, a cartilaginous choristoma of the crest of the alveolar ridge in a denture wearer is called a Cutright tumor.

Osseous choristoma should not be confused with the dystrophic calcification so frequently found in old thrombi, hematomas and keratin-filled soft tissue cysts. This darkly staining aggregation of precipitated salts does not have a bone-like organization.

Treatment and Prognosis

The choristoma is best treated by conservative surgical excision. No recurrences have been reported with this therapy.

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