Fibrous Dysplasia

Source:  Fibrous Dysplasia    Tag:  monostotic fibrous dysplasia
 Fibrous dysplasia is usually a benign condition in which normal bone is replaced by fibrous connective tissue ( malignant transformation occurs in less than 1%). Most lesions occur in the ribs or craniofacial bones, especially maxilla.
Anatomical patterns may be Monostotic: most common,Polyostotic: 25%, & as part of McCune-Albright sdyndrome.
Clinically it may present as incidental finding, local pain, local swelling, pathologic fracture, cranial nerve compression
Fibrous dysplasia consists of proliferative connective tissue, causing thickening of bones.
There are 3 forms: Compact form, Lytic form and Pseudo pagetoid form.
1. Compact form is a dense thickening of bone , especially of the skull base, resulting in ground glass appearance. It may cause stenosis of the optic foramen , superior orbital fissure,  shallow orbits with proptosis, sellar and sphenoid involvement causing hypopituitarism and expansion of the temporal bone and greater wing of the sphenoid.
2. Lytic form takes the shape of a radiolucent area limited by a thin sclerotic line.
3. Pseudo pagetoid form is characterized by a combination of both sclerotic and  radiolucent lesions. The lesion stabilizes after the age of 25-30. There is a small risk of malignant transformation.

Investigation: Rraised serum alkaline phosphatase level,X Ray, CT scan & MRI.
Treatment of calvarial kesions: curettage and cranioplasty.

Sources: Manual of Neurosurgery,  Ramamurthy & Tandon, (jaypee publishers)
               Handbook of neurosurgery Greenberg, 7th ed ( Thieme)