Intraosseous Hemangioma of the Occipital Bone

They are slow growing benign vascular malformations which account for 0.2 % of all skull vault bone neoplasms . typically occur in women in the fourth and fifth decades of life. Classically they of 3 types : Cavernous , capillary and venous. Cavernous type is the most common and presents as large thin walled endothelium lined vascular channels.These channels are interspersed among bony trabeculae giving it the characteristic soap bubble appearance on xray. Capillary type presents as sun burst pattern due to its fine vascular network pattern. Pathologically they are due to overgrowth of vascular channels within the bone. Histologically their picture may range from predominantly fatty lesions to predominantly vascular stroma. Most commonly involve the spine and the skull especially the parietal and frontal bones. Less commonly, they arise from craniofacial bones, including the zygoma, maxilla, vomer, and mandible They typically occur within the diploic space causing a greater expansion of the outer table than the inner table and therefore producing a palpable lump. Cavernous hemangiomas are mostly solitary lesions; however, multifocal cavernous hemangiomas have been reportedThe increase in hemangioma size is probably due to repeated hemorrhage which can be picked on MRI due to hemosiderine deposits Usually hemangiomas from spine are symptomless unless they are large enough to cause intraspinal extension or compress surrounding structures.So also hemangiomas from frontal and parietal bone wil produce symptoms only if there is intracranial extension. However hemangioma from bones forming the skull base are mostly associated with symptoms causing them to be misconfused with the more commonly occurring skull base tuomurs .Some examples of skull base hemangiomas that have been reported to arise from the occipital condyle have been noted to cause neck pain and torticollis, similarly from the foramen magnum and clivus causing basilar impression, and from the orbitosphenoidal ridge and orbital roof causing progressive proptosis and visual loss. RADIOGRAPHIC CHARACTERISTICS: On an Xray they present as an expansive, well–circumscribed area of rarefaction with radiating trabeculations appearing as a sun burst pattern or soap bubble pattern These characteristics are better defined on CT, especially for smaller lesions that are not obvious on plain radiographs. The cortex can be greatly expanded leaving a thin bony shell, but the periosteum remains intact. On MRI the lesion usually appears heterogeneous with variablesignal intensities on both T1– and T2–weighted images. The signal depends on the quantity of slow–moving venous blood and on the ratio of red marrow to converted fatty marrow present within the lesion. On T1–weighted imaging, smaller lesions tend to have increased intensity whereas larger lesions typically show low signal intensity within the trabeculae. Lesions with more fatty marrow show increased signal intensity on T1–weighted images. Pure cavernous hemangioms typically enhance after gadolinium is administered. On T2–weighted imaging, areas of increased signal intensity correspond to slow flow or pooling of blood. Angiography of larger hemangiomas typically demonstrates a hypervascular lesion and a delayed blush with feeding arteries but no draining veins. Preoperative embolization may be helpful in the management of larger vascular lesions. On scintigraphy hemangioms show increased activity on delayed phase on the bone scan.Here its difficult to distuinguish it from Pagets disease and sclerotic metastasis. They may rarely have a dural tail sign on MR. DIFFERENTIAL DIAGNOSIS: Intraosseous hemangiomas are to be differentiated from osteogenic sarcomas, which destroy the bone cortex and invade the periosteum and surrounding soft tissues. There is usually no reactive sclerosis at the margins.