Benign Skull Tumors
- Author: Draga Jichici, MD, FRCP, FAHA; Chief Editor: Tarakad S Ramachandran, MBBS, FRCP(C), FACP more...
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 skull-base surgery techniques have provided access to previously inoperable skull tumors. 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 is an important diagnostic tool. The initial classification of a lesion into radiolucent (osteolytic) or radiopaque (osteoblastic) 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 important. Head CT scanning, with and without contrast, is useful in determining the extent of intracranial extension and other tumor characteristics.
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]
Epidemiology
Frequency
United States
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 and 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), 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.
Wilkins RH, Rengachary SS. 2nd ed. Neurosurgery. New York, NY: McGraw-Hill; 1996:1503-1528.
Huvos AG. Bone Tumors: Diagnosis, Treatment and Prognosis. Philadelphia, Pa: WB Saunders Company; 1979.
Yuca K, Kiris M, Avcu S, Bayram I, Cankaya H, Kiroglu AF. A giant paediatric mandibular aneurysmal bone cyst and reconstruction with bilateral iliac bone graft. B-ENT. 2009;5(1):39-42. [Medline].
Nasser MJ. Psammomatoid ossifying fibroma with secondary aneurysmal bone cyst of frontal sinus. Childs Nerv Syst. May 30 2009;[Medline].
Docquier PL, Delloye C, Galant C. Histology can be predictive of the clinical course of a primary aneurysmal bone cyst. Arch Orthop Trauma Surg. May 9 2009;[Medline].
Konishi E, Okubo T, Itoi M, Katsumi Y, Murata H, Yanagisawa A. Chondroblastoma of trapezium with metacarpal involvement. Orthopedics. Apr 2008;31(4):395. [Medline].
Schmitz-Feuerhake I, Pflugbeil S, Pflugbeil C. Radiation Risks from Diagnostic Radiology: Meningiomas and other Late Effects after Exposure of the Skull. Gesundheitswesen. Jun 23 2009;[Medline].
Wootton-Gorges SL. MR imaging of primary bone tumors and tumor-like conditions in children. Magn Reson Imaging Clin N Am. Aug 2009;17(3):469-87, vi. [Medline].
Yucel E, Akkaya H, Gürkanlar D, Ergun T. Congenital cavernous hemangioma of the skull. Turk Neurosurg. 2011;21(4):645-7. [Medline].
Bloch O, Kaur G, Jian BJ, Parsa AT, Barani IJ. Stereotactic radiosurgery for benign meningiomas. J Neurooncol. Oct 18 2011;[Medline].
Dassoulas K, Schlesinger D, Yen CP, Sheehan J. The role of Gamma Knife surgery in the treatment of skull base chordomas. J Neurooncol. Mar 11 2009;[Medline].
Burger PC, Scheithauer BW, Vogel FS. 4th ed. Surgical Pathology of the Nervous System and its Coverings. New York, NY: Churchill Livingstone; 2002:1-66.
Keyserling H, Peterson K, Camacho D, Castillo M. Giant cell angiofibroma of the orbit. AJNR Am J Neuroradiol. Aug 2004;25(7):1266-8. [Medline].
Mirra JM. Bone Tumors: Clinical, Radiological and Pathological Correlations. Philadelphia, Pa: Lea and Febiger; 1989.
Morris JM, Lane JI, Witte RJ, Thompson DM. Giant cell reparative granuloma of the nasal cavity. AJNR Am J Neuroradiol. Aug 2004;25(7):1263-5. [Medline].
Thomas JE, Baker HL Jr. Assessment of roentgenographic lucencies of the skull: a systematic approach. Neurology. Feb 1975;25(2):99-106. [Medline].
Unni KK. 5th ed. Dahlin's Bone Tumors: General Aspects and Data on 11,087 Cases. Philadelphia, Pa: Lippincott Williams & Wilkins; 1996.
Youmans JR. 5th ed. Neurological Surgery. Philadelphia, Pa: WB Saunders Company; 2004:3227-3268.

