Fibrous dysplasia of the right maxillary sinus, displacing the floor of the orbit and causing proptosis of the right eye.
Fibrous dysplasia of the left ethmoid sinus producing widening of the nasal bridge and proptosis of the left eye. The CT scan of this patient and his surgery are depicted below.
Axial CT scan showing the ground glass appearance of the fibrous dysplasia. The lesion is bulging into the left orbit.
Coronal CT scan showing involvement of the left ethmoid. The lesion bulges into the left orbit and displaces the nasal septum to the right.
An external ethmoidectomy approach is used to expose the lesion which is drilled out and removed.
FIBROUS DYSPLASIA is a localized disorder of bone characterized by abnormal proliferation of fibrous tissue interspersed with normal or immature bone, endocrine dysfunction, abnormal pigmentation, and precocious puberty in girls.
Currently, 3 general subtypes of disease are recognized: monostotic, polyostotic, and McCune-Albright syndrome. The monostotic form is the mildest and most common form (approximately 70% of cases), is noted for lesions involving the ribs and craniofacial bones, and is typically diagnosed between ages 20 and 30 years. The polyostotic form (30% of cases) has an earlier onset, typically in childhood, and affected patients tend to have more severe skeletal and craniofacial involvement. The most severe form of the disorder, McCune-Albright syndrome (3% of cases), is more commonly found (although not exclusively) in females, is associated with short stature due to premature closure of the epiphyses, and is associated with endocrine abnormalities and pigmented cutaneous lesions.
Histologic exam shows irregular trabeculae of woven bone intermixed with a connective tissue stroma. Lesions will vary in the amount and distribution of bone and in the cellularity and vascularity of the fibrous stroma.
Within the skull base, a known variant of this classic pathologic picture is a distinct histologic pattern of "cementicles," small bony spicules resembling pieces of a puzzle, interspersed throughout the lesion. This is a variant that is unique to the skull and is not found in lesions occurring in the long bones of the body. These lesions are characterized by a loose fibrous background and darkly stained cemented ossicles surrounded by reactive bone.