Cranial osteoma is a common benign tumor characterized by slow growth, painlessness, and wide base. The cranial demarcation is often unclear. It can occur in any part of the skull, and is more common in the frontal and parietal bones, and less common in other cranial bones and the base of the skull. Pathogenesis Skull osteomas are divided into two major groups: dense osteomas and cancellous osteomas. Dense osteoma mostly originates from the outer plate of the bone, and the inner plate remains intact, which is similar to normal bone under the microscope, and some of them can be seen as osteogenic connective tissue with new bone tissue inside. Some of them can be seen as osteogenic connective tissue with new bone tissue inside. Because of its density and hardness, it is also called ivory osteoma. Pontine osteoma originates from the plate barrier and contains more fibrous tissue and sometimes red bone marrow or fatty bone marrow. Disease Examination On cranial radiographs, round or oval, confined, high-density shadows are usually seen. The cancellous type of osteoma is internally lax and unevenly dense, and calcification may be present within the trabeculae. Dense osteoma usually grows on the outer plate of the skull, bulges outward, and has a dense and homogeneous internal structure. Osteomas occurring in the frontal sinus and sieve sinus are often lobulated. Clinical diagnosis Because of the slow growth of the tumor, it is easy to be ignored in the early stage, and the course of the disease is long, and some of them can stop growing by themselves. Most of the osteomas are located in the top of the skull, and the plate type is common, which is a round or cone-shaped bulge protruding from the outer plate of the top of the skull, ranging in size from several millimeters to several centimeters in diameter, with no adhesion with the scalp, no pressure pain, and no discomfort, and it does not cause any special symptom, except for causing deformation of the appearance. Plate barrier type is mostly expansive growth, with wider range and more rounded cranial protrusion, which may cause local pain in the corresponding parts. Inner plate type is mostly intracranial growth, which is rare clinically, but when the osteoma protrudes into the paranasal sinuses and orbits, such as when the osteoma is larger, it may cause corresponding symptoms. Osteoma in paranasal sinus often has isthmus and sinus wall connection, and osteoma enlargement blocks the outlet of paranasal sinus, which makes it one of the causes of paranasal sinus mucus cyst. Sial sinus osteoma protruding into the orbit can cause proptosis and visual impairment. According to the clinical manifestations and skull X-ray or skull CT examination, it is not difficult to make a diagnosis of osteoma. It should be differentiated from the secondary hyperplasia of the skull caused by meningioma. Meningioma mostly involves the whole layer of the skull, while osteoma usually only involves the inner plate; meningioma can be seen as widening of the meningeal vascular grooves, and radial hyperplasia of the skull can be seen in cut radiographs, and the signs of meningioma can be seen in the CT examination while displaying the bony changes of the skull. The disease should also be differentiated from abnormal bone fiber hyperplasia, which has a wider range of lesions, is more common at the top of the orbit, with facial changes, and is visible on X-ray plain film and CT as a full-layer involvement of the cranial bone, with poorly defined borders and inconsistent densities, and may have changes in the flat bones of other parts of the body. Treatment The treatment of osteoma is mainly based on surgery. Osteomas at the top of the skull may be left untreated if they are small in size and have no special symptoms, or if the growth of individual osteoma has stopped. For fast-growing osteoma that affects the face and has symptoms, it should be surgically removed. For osteomas limited to the outer plate, only chiseling or smoothing is necessary, and the residual base does not need to be inactivated by electrocautery. For large, intracranial osteomas, bone flap resection is required, and the tumor-carrying bone flap is inactivated by boiling for 30 min and placed back after plastic treatment. For the osteoma involving paranasal sinuses, if it has caused obstruction of paranasal sinuses, surgical resection should be carried out; frontal sinus osteoma should be resected by transfrontal epidural approach; sieve sinus osteoma can be resected by transorbital or transorbital plate approach. Osteomas of the cancellous bone need to be removed completely to avoid recurrence.