Chondroma of dural convexity, WHO grade I
Intracranial chondromas are benign cartilaginous tumors that usually arise from the base of the skull but may also originate intradurally from the dura mater of the convexity or falx cerebri (3). They are uncommon, with an estimated incidence of approximately 0.2-0.3% of intracranial neoplasms (1). Because of their rarity, chondroma of the dura often is not entertained in the differential diagnosis and the usual preoperative diagnosis is meningioma, given the similar imaging and clinical presentation of these two dural masses (9).
Despite their benignity and rarity, these tumors deserve due consideration to exclude the possibility of a malignant chondroid lesion. Chondrosarcomas are even rarer intracranial neoplasms than chondromas, with an estimated incidence of 0.16% (5). An initial impression of chondroma on histology should prompt careful search for any worrisome features that meet the criteria for a diagnosis of chondrosarcoma, such as hypercellularity, cytologic atypia, increased mitotic activity and increased nuclear size with some lacuna containing greater than one nucleus (3, 5). The treatment for chondrosarcomas may involve both surgical resection and adjuvant radiation therapy, whereas surgery alone adequately treats chondromas. Since occasional previous reports link adjuvant irradiation of chondromas with increased malignant degeneration (1), radiation should be avoided post operatively.
Intracranial chondromas may occur at any age, although they are most frequently seen in younger individuals with a peak in the third decade (3). They are usually solitary lesions but may be a component of Maffucci's syndrome (multiple enchondromata and hemangiomata) or Ollier's disease (enchondromatosis without hemangiomata) (4, 6, 10). In both of these syndromes, the chondromas may undergo malignant transformation. Chondromas have also been reported in Noonan's syndrome (2). This patient's post operative clinical workup was negative for these conditions.
The etiology of intracranial chondromas, and a related dural lesion, osteochondromas, remains controversial. It is generally accepted that skull-based lesions arise from cartilage rests in the synchondrosis. Proposed sources of convexity and falx tumors are more varied and include cartilaginous metaplasia of meningeal fibroblasts (possibly activated by trauma or inflammation), pluripotent mesenchymal cells in the dura mater, ectopic rests of cartilaginous tissue, and traumatic displacement of cartilage (1, 3, 7, 9). One prior report observed a focus of metaplastic transition between fibroblastic tissue and chondroid which strengthens the theory of metaplasia as one origin for these tumors (9). In this present case we did not observe areas of chondroid metaplasia in the dura adjacent to the mass. Given the patient's involvement in motocross, it is tempting to speculate about a relationship between the chondroma and past history of trauma; however, no features of remote subdural hematoma were identified either on neuroimaging or in the surgical resection specimen.
Chondromas are slow growing lesions which may not produce symptoms for years. They are usually either detected incidentally on imaging (like this case) or when their size results in symptoms related to mass effect (9). While on neuroimaging studies chondromas and osteochondromas often resemble meningiomas, the absence of a dural tail, avascularity, and patchy enhancement favor a diagnosis of chondroma.
This patient's tumor did not exhibit features of a chondrosarcoma and her lesion was slowly growing. Nevertheless, surgical removal of benign chondromas is warranted to mitigate the even low potential for malignant transformation and to prevent any future problems related to the mass effect of the lesion.
Contributed by Hilary Somerset, MD; C. Corbett Wilkinson, MD; B.K. Kleinschmidt-DeMasters, MD