Imaging description

Primary bone disorders involving the skull base present with non-specific MRI appearances. While MRI is very helpful in delineating the extent of involvement it is not as helpful in providing a specific diagnosis. In primary osseous abnormalities of the skull base, combining MR with high-resolution bone CT is essential.

Fibrous dysplasia (FD) is a common benign bone disorder secondary to replacement of normal bone marrow by woven bone and fibrous tissue. It can be lytic or sclerotic or polyostotic and can involve any bone in the body [1]. The involvement of calvarium, skull base, and facial bones is seen in about 50% of the cases of polyostotic FD. There are three distinct imaging patterns based on CT findings. The most common is a mixed pagetoid pattern (Fig. 57.1) with areas of radiolucency and radiodensity and bone expansion. A sclerotic FD with ground-glass density (Fig. 57.2) and a predominantly cystic FD with central lucency and sclerotic borders (Fig. 57.3) are the other varieties. The MRI appearance of FD is variable, ranging from avidly enhancing lesions to no enhancement, and from markedly hyperintense T2 signal to markedly hypointense T2 signal [2].