Background

Tumors of the skull are uncommon lesions that are not reported systematically in the medical literature. Therefore, assessing their true incidence and consequences to the health of the general population is difficult. Recent diagnostic advances have made such lesions easier to recognize, and new endonasal approaches to the skull base have significantly advaced our abilities to treat tumors located there. Skull tumors are estimated to account for approximately 1% of bone tumors.

Treatment for most tumors is not controversial. However, the differentiation and identification of the tumor type is the greatest clinical challenge. The usual presentation is an enlarging skull mass, with or without pain, or cranial nerve deficits if the tumor involves the base of the skull.

Plain skull radiography with special projections used to be an important diagnostic tool. Head CT scanning, with and without contrast, is the most useful investigation in determining the nature and extent of skull base tumors. The initial classification of a lesion into radiolucent (osteolytic) or radiopaque (osteoblastic) based on plain radiographs or CT scan is of considerable significance. The presence of sharply defined or irregular margins, presence or absence of sclerotic borders, and calcifications in the lesion are also vital to establish a tentative diagnosis.

Most skull tumors share certain MRI characteristics, such as hypointensity on T1-weighted images, hyperintensity on T2-weighted images, and some degree of contrast enhancement. The capability of imaging in multiple planes and enhanced soft tissue discrimination has made MRI an important diagnostic tool. The classification of benign and malignant brain tumors is based on that by Wilkins and Rengachary^[1](which is a modified version of the system outlined by Huvos^[2]).

Pathophysiology

The tumor type and behavior determine radiographic appearance (eg, radiolucent, radiopaque). Depending on the primary proliferating cell, benign skull tumors can be any of the following:

Bone forming
Cartilage forming
Tumors of connective tissue
Histiocytic tumors
Tumors of blood or blood vessel origin
Other types, including fibrous dysplasia, Paget disease, or epidermoid, dermoid, or aneurysmal bone cysts^{[3, 4, 5]}

Frequency

One of the most comprehensive series of bone tumors with classification originated from the Mayo Clinic. Of the 7975 patients in the series, 4% had tumors involving the skull (excluding the mandible, maxilla, and nasal cavity). Of these tumors, 19% were benign and 81% were malignant. Because the Mayo Clinic is a tertiary referral center, this series probably reflects some degree of selection bias. Other studies estimate that skull tumors comprise 1% of bone tumors.

Bone-forming tumors: Osteomas are the most common primary brain tumors of the calvaria, affecting 0.4% of the general population. Osteoid osteomas are very common, but ossifying fibromas are rare. Osteoblastomas account for approximately 1% of bone tumors.

Cartilage-forming tumors: Chondromas and chondromyxoid fibromas are rare. Chondroblastoma, although rare in some studies, accounted for 10% of the benign skull tumors in the Mayo series.

Connective tissue tumors: Desmoplastic fibroma is very rare in the skull (in the literature, only case reports exist).

Histiocytic tumors: Giant cell granuloma, nonossifying fibroma, and xanthoma are very rare in the skull.

Tumors of blood or blood vessel origin: Eosinophilic granuloma commonly affects the skull. Hemangiomas account for 10% of benign skull tumors (70% in the Mayo series).

Lymphangiomas: These tumors are rare.

Miscellaneous conditions: Aneurysmal bone cysts, epidermoid and dermoid tumors, intraosseous meningiomas, and fibrous dysplasia are relatively rare conditions. The prevalence of Paget disease is believed to be 1-5% in those older than 40 years, with involvement of any bone in the body, but most individuals remain asymptomatic and the condition is undiagnosed.

Mortality/Morbidity

Morbidity is due to recurrent sinusitis (tumors affecting sinuses or skull base), recurrence of tumor after excision, and cranial nerve compression at the skull base.

Malignant transformation to osteosarcoma, fibrosarcoma, or chondrosarcoma is observed in 2% of patients with Paget disease and 0.5% of patients with fibrous dysplasia.

Sex

Most tumors demonstrate no sex predilection.

Osteomas, ossifying fibromas, chondromas, and giant cell granulomas are observed more often in females than in males.

Osteoid osteomas, osteoblastomas, eosinophilic granuloma, and Paget disease affect males more often than females.

The female-to-male ratio of hemangiomas is 1:2.

Age

Bone-forming tumors, connective tissue tumors, giant cell granulomas, and fibrous dysplasias usually manifest in young adults. Cartilage-forming tumors affect those aged 20-50 years.

Eosinophilic granuloma, nonossifying fibroma, and xanthoma usually manifest in those younger than 20 years. Epidermoids, dermoids, and lymphangiomas are usually observed in children.

The usual age of presentation for hemangiomas is in the fourth to sixth decade of life. Intraosseous meningioma and Paget disease affect those older than 50 years.

Prognosis

Prognosis varies very considerably based on the nature, location (basal vs calvarial) and size of the tumor, among other factors.

Clinical Presentation

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Media Gallery

Composite CT scan, MRI, and angiogram of a symptomatic ossifying fibroma with extensive involvement of the skull base in a 12-year-old girl whose primary symptom was exophthalmos and loss of vision bilaterally.
Lateral skull radiograph of a 73-year-old patient with a slow-growing, nontender skull lesion. Note the typical honeycomb appearance.
Head CT scan of a 73-year-old patient with a slow-growing, nontender skull lesion shows a well-defined nonenhancing lytic lesion with calcification and honeycomb appearance.
Sagittal magnetic resonance imaging (MRI) section of the brain of a 73-year-old patient with a slow-growing, nontender skull lesion showing a nonenhancing soft tissue mass. This lesion proved to be a hemangioma.
Lateral skull radiograph of a 17-year-old adolescent male with a painless slow-growing mass. The single round lytic lesion was found to be an epidermoid.
Fibrous dysplasia involving the sphenoid sinus and pterygoid plates as well as the sella. This is an asymptomatic lesion; observation was recommended.
Head CT scan of a 78-year-old woman with Paget disease. Note the cotton wool appearance of the lesion, with varying degrees of bone formation and no clear edges. Observation was recommended.
A well-preserved 90-year-old female patient with a mass in the occiput with an inability to sleep and rapid atrial fibrillation related to hyperthyroidism due to a solitary thyroid metastasis. This sagittal CT scan demonstrates a lytic lesion.
Same patient as above with mixed attenuation calvarial and epidural mass on MRI; lesion was resected.
A 49-year-old male patient with occipital headache and no deficits. A CT scan demonstrates an expansile lesion involving the diploe. This was demonstrated to be a dermoid tumor at histopathology.
Same patient as above with an expansile lesion involving the diploe on MRI.
A 56-year-old female patient with a small bump on her forehead which slowly increased in size over a 5-year period. A CT scan revealed a lesion which was resected with endoscopic assistance so the incision would be in the hairline. Histopathological examination confirmed an osteoid osteoma.
Axial and coronal CT scan images of a 40-year-old female patient with progressive visual decline in the left eye for >2 years. Patient was blind at presentation. A cranial resection was done with resulting return of light perception. Histopathological examination confirmed an intraosseous meningioma.
Coronal T1 and axial T2 images for same patient as above.
MRI images of a 40-year-old patient with a visual field defect in the left temporal (Ollier disease). Both lesions were resected and shown to be osteochondromas on histopathological examination.
CT scan images for same patient as above.
Axial and coronal T1 MRI images of a 65-year-old patient with a chronically large jaw who presented with h/a and left visual worsening due to fibrous dysplasia. Transnasal surgery combined with an eyelid approach was completed to open up the frontal sinus ostium and decompress the orbit.
Coronal and sagittal CT bone window images of same patient as above.

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Author

Draga Jichici, MD, FRCPC, FAHA Associate Clinical Professor, Division of Medicine, Department of Critical Care Medicine and Neurology, Co-Director, Neurosurgical Intensive Care Unit, Co-Director, Transcranial Doppler Ultrasound, Hamilton Health Sciences, McMaster University School of Medicine, Canada

Draga Jichici, MD, FRCPC, FAHA is a member of the following medical societies: American Academy of Neurology, Canadian Critical Care Society, Canadian Medical Protective Association, Canadian Neurocritical Care Society, Canadian Neurological Sciences Federation, Neurocritical Care Society, Royal College of Physicians and Surgeons of Canada

Disclosure: Nothing to disclose.

Coauthor(s)

Kesava KV Reddy, MBBS Head of Service-Neurosurgery, St Joseph’s Hospital; Chief of Surgery, Hamilton General Site, Hamilton Health Sciences; Clinical Professor, Department of Surgery, McMaster University School of Medicine, Canada

Kesava KV Reddy, MBBS is a member of the following medical societies: American Association of Neurological Surgeons, American College of Surgeons, Canadian Consortium on Adult Hydrocephalus, Canadian Neurosurgical Society, College of Physicians and Surgeons of Ontario, Congress of Neurological Surgeons, Hamilton Academy of Medicine, North American Skull Base Society, Ontario Medical Association

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Jorge C Kattah, MD Head, Associate Program Director, Professor, Department of Neurology, University of Illinois College of Medicine at Peoria

Jorge C Kattah, MD is a member of the following medical societies: American Academy of Neurology, American Neurological Association, New York Academy of Sciences

Disclosure: Nothing to disclose.

Chief Editor

Tarakad S Ramachandran, MBBS, MBA, MPH, FAAN, FACP, FAHA, FRCP, FRCPC, FRS, LRCP, MRCP, MRCS † Professor Emeritus of Neurology and Psychiatry, Clinical Professor of Medicine, Clinical Professor of Family Medicine, Clinical Professor of Neurosurgery, State University of New York Upstate Medical University; Neuroscience Director, Department of Neurology, Crouse Irving Memorial Hospital

Tarakad S Ramachandran, MBBS, MBA, MPH, FAAN, FACP, FAHA, FRCP, FRCPC, FRS, LRCP, MRCP, MRCS is a member of the following medical societies: American Academy of Neurology, American Academy of Pain Medicine, American College of Forensic Examiners Institute, American College of International Physicians, American College of Physicians, American Heart Association, American Stroke Association, National Association of Managed Care Physicians, Royal College of Physicians, Royal College of Physicians and Surgeons of Canada, Royal College of Surgeons of England, Royal Society of Medicine

Disclosure: Nothing to disclose.

Additional Contributors

Spiros Manolidis, MD Associate Professor of Otolaryngology and Neurological Surgery, Columbia University

Spiros Manolidis, MD is a member of the following medical societies: American Academy of Otolaryngology-Head and Neck Surgery, American Auditory Society, American Head and Neck Society, American Medical Association, Canadian Society of Otolaryngology-Head & Neck Surgery, Society of University Otolaryngologists-Head and Neck Surgeons, Texas Medical Association

Disclosure: Nothing to disclose.

Acknowledgements

The authors and editors of Medscape Reference gratefully acknowledge the contributions of previous author Efstathios Papavassiliou, MD to the development and writing of this article.