Benign Skull Tumors

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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:

Epidemiology

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. 

History

The challenge is to differentiate the varying types of bone tumors. Imaging studies and the appearance of the lesion are the primary differentiating factors. The location of the lesion is of little differential diagnostic value, although lesions of developmental origin have a strong midline propensity.

Single, small, grossly round and oval lesions are more likely to be benign. The presence of peripheral sclerosis strongly favors a benign tumor. The margin of a lesion is of no diagnostic value.

Intralesional calcifications are more common in benign tumors. Peripheral bone vascularity also indicates a benign process.

The differential diagnosis includes encephalocele, meningoencephalocele, venous lakes of the skull, pacchionian depression, fractures, surgical defects, osteomyelitis, tuberculosis, syphilis, osteoporosis, and congenital hemolytic anemia.

The following tumors manifest as slow-growing painless masses: osteoma, ossifying fibroma, chondroma, nonossifying fibroma, xanthoma, hemangioma, epidermoid, dermoid, meningioma, and fibrous dysplasia.

Other tumors include osteoid osteoma, osteoblastoma, chondroblastoma,[6] chondromyxoid fibroma, desmoplastic fibroma, giant cell granuloma, eosinophilic granuloma, and aneurysmal bone cyst.

Associated headache is nonspecific in nature.

Lymphangioma manifests as a painless cystic defect.

Osteoid osteoma manifests with nocturnal local tenderness that is relieved by aspirin or nonsteroidal anti-inflammatory drugs (NSAIDs).

Cranial nerve deficits are observed in chondroblastoma, giant cell granuloma, epidermoid, dermoid, fibrous dysplasia, and Paget disease.

A rapidly growing mass is observed in desmoplastic fibroma and giant cell granuloma.

Tumor location is unreliable for diagnosis. However, certain tumors appear at the convexity more than the skull base and vice versa.

Physical

Physical findings vary according to tumor type.

Causes

Benign skull tumors are sporadic in occurrence. However, specific syndromes involving skull tumors have been described.

Complications

Complications of nontreatment vary based on the nature, size, extent, and location of the tumor. 

Laboratory Studies

Laboratory studies are not helpful in making the diagnosis.

Imaging Studies

Plain skull radiography and head CT scanning[7]

Magnetic resonance imaging[8]

Bone scanning: Bone scanning with technetium Tc-99m shows an area of increased radioisotope uptake in osteomas, ossifying fibromas, and osteoblastomas.

Arteriography

Procedures

Biopsy of the lesion is of paramount importance for establishing the diagnosis and considering treatment options.

Histologic Findings

Osteomas are composed of mature lamellar bone. The typical appearance is a nidus of osteoid tissue in a background of osteoblastic connective tissue, which is enclosed completely by reactive bone. Ossifying fibroma consists of fibrous spindle cells with varying amounts of woven bone. The periphery of the tumor is composed of mature lamellar bone.

Osteoblastoma consists of a fibrous stroma with irregular osteoid deposition. Chondromas (enchondroma, juxtacortical chondroma, osteochondroma) are rare skull tumors consisting of mature hyaline cartilage. Chondroblastomas consist of immature cartilage cells.

Chondromyxoid fibroma is characterized by chondroid and myxoid differentiation with lobular growth. Desmoplastic fibroma is of fibrous connective tissue origin marked by the formation of collagen. Giant cell granuloma manifests with giant cells around hemorrhagic foci, numerous spindle-shaped fibroblastic cells, and new bone formation. The tumor cells are smaller than those of the giant cell tumor of the bone, whereas stromal cells and giant cells resemble each other.

Nonossifying fibroma and xanthoma consist of fibroblast proliferation with multinucleated giant cells and foamy xanthomatous cells. In eosinophilic granuloma, mononuclear histiocytes are mixed with eosinophils. Giant cells and areas of hemorrhage or necrosis may also be observed. The histiocytes stain positive for the protein S-100. On electron microscopy, the Birbeck granules that characterize the Langerhans or X cells are noted. Hemangiomas are visualized macroscopically as brownish red lesions under the skull periosteum. Microscopically, they consist of capillary, cavernous, or venous blood vessels.[9]

Lymphangiomas consist of lymph vessels. Aneurysmal bone cysts consist of large vascular spaces separated by trabeculae of connective tissue and bone. The vascular spaces lack endothelial lining. Epidermoids consist of an epithelial capsule filled by desquamated epithelial cells and keratin.

Dermoids usually contain hair follicles and sebaceous and sweat glands. Fibrous dysplasia is a developmental anomaly in which the normal bone formation is arrested at the woven stage; thus, lamellar bone is not formed. This results in an overgrowth of the fibrous tissue among woven bone, which is the typical histologic feature of this lesion. Paget disease is initially characterized by increased osteoclastic activity, which results in bone resorption, followed by increased osteoblastic activity and bone formation.

Medical Care

Administer aspirin or NSAIDs for osteoid osteoma.

Provide pain control symptomatically.

No treatment is required for asymptomatic lesions unless diagnostic concerns exist.

Stereotactic radiosurgery should be considered as an alternative to surgical resection for benign meningiomas.[10]

Surgical Care

Complete surgical excision when feasible is ideal for benign skull tumors for symptomatic relief, cosmetic reasons, or cranial nerve/neural decompression.

En bloc resection is the preferred intervention though this may not be possible for skull base lesions, especially those of a chondroid nature.

Curettage is also performed for lesions that cannot be resected completely. Careful removal of the cyst wall is critical in epidermoids and dermoids. Gamma Knife and CyberKnife are possible new ways of treating unresectable symptomatic lesions.[11]

Extended endonasal approaches to skull base lesions are now accepted methods of accessing hitherto difficult-to-access lesions. Endoscopy is also being used in simple osteoid osteomas of the forehead for cosmetic purposes.

Consultations

See the list below:

Medication Summary

The goals of pharmacotherapy are to reduce morbidity and prevent complications.

Ibuprofen (Motrin, Advil, Haltran, Nuprin)

Clinical Context:  DOC for mild to moderate pain. Inhibits inflammatory reactions and pain by decreasing prostaglandin synthesis.

Class Summary

Have analgesic, anti-inflammatory, and antipyretic activities. Their mechanism of action is not known but may inhibit cyclooxygenase activity and prostaglandin synthesis. Other mechanisms may exist as well, such as inhibition of leukotriene synthesis, lysosomal enzyme release, lipoxygenase activity, neutrophil aggregation, and various cell membrane functions.

Acetaminophen with codeine (Tylenol #3)

Clinical Context:  Indicated for treatment of mild to moderate pain.

Oxycodone and acetaminophen (Percocet)

Clinical Context:  Drug combination indicated for relief of moderate to severe pain; DOC for aspirin-hypersensitive patients.

Hydrocodone bitartrate and acetaminophen (Vicodin ES)

Clinical Context:  Drug combination indicated for moderate to severe pain.

Class Summary

Pain control is essential to quality patient care. These agents ensure patient comfort, promote pulmonary toilet, and have sedating properties, which are beneficial for patients who have moderate to severe pain.

Aspirin (Anacin, Ascriptin, Bayer Aspirin)

Clinical Context:  Treats mild to moderate pain and headache. Inhibits prostaglandin synthesis, which prevents formation of platelet-aggregating thromboxane A2.

Class Summary

Can reduce inflammation and pain symptoms.

Further Outpatient Care

See the list below:

Further Inpatient Care

Inpatient care is not usually required unless skull-base surgery is needed for nerve decompression.

Complications

See the list below:

Prognosis

See the list below:

Patient Education

See the list below:

Author

Draga Jichici, MD, FRCP, FAHA, Associate Clinical Professor, Department of Neurology and Critical Care Medicine, McMaster University School of Medicine, 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

Disclosure: Nothing to disclose.

Specialty Editors

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

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

Disclosure: Nothing to disclose.

Additional Contributors

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

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.

References

  1. Wilkins RH, Rengachary SS. 2nd ed. Neurosurgery. New York, NY: McGraw-Hill; 1996. 1503-1528.
  2. Huvos AG. Bone Tumors: Diagnosis, Treatment and Prognosis. Philadelphia, Pa: WB Saunders Company; 1979.
  3. 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. [View Abstract]
  4. Nasser MJ. Psammomatoid ossifying fibroma with secondary aneurysmal bone cyst of frontal sinus. Childs Nerv Syst. 2009 May 30. [View Abstract]
  5. Docquier PL, Delloye C, Galant C. Histology can be predictive of the clinical course of a primary aneurysmal bone cyst. Arch Orthop Trauma Surg. 2009 May 9. [View Abstract]
  6. Konishi E, Okubo T, Itoi M, Katsumi Y, Murata H, Yanagisawa A. Chondroblastoma of trapezium with metacarpal involvement. Orthopedics. 2008 Apr. 31(4):395. [View Abstract]
  7. Schmitz-Feuerhake I, Pflugbeil S, Pflugbeil C. Radiation Risks from Diagnostic Radiology: Meningiomas and other Late Effects after Exposure of the Skull. Gesundheitswesen. 2009 Jun 23. [View Abstract]
  8. Wootton-Gorges SL. MR imaging of primary bone tumors and tumor-like conditions in children. Magn Reson Imaging Clin N Am. 2009 Aug. 17(3):469-87, vi. [View Abstract]
  9. Yucel E, Akkaya H, Gürkanlar D, Ergun T. Congenital cavernous hemangioma of the skull. Turk Neurosurg. 2011. 21(4):645-7. [View Abstract]
  10. Bloch O, Kaur G, Jian BJ, Parsa AT, Barani IJ. Stereotactic radiosurgery for benign meningiomas. J Neurooncol. 2011 Oct 18. [View Abstract]
  11. Dassoulas K, Schlesinger D, Yen CP, Sheehan J. The role of Gamma Knife surgery in the treatment of skull base chordomas. J Neurooncol. 2009 Mar 11. [View Abstract]
  12. 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.
  13. Keyserling H, Peterson K, Camacho D, Castillo M. Giant cell angiofibroma of the orbit. AJNR Am J Neuroradiol. 2004 Aug. 25(7):1266-8. [View Abstract]
  14. Mirra JM. Bone Tumors: Clinical, Radiological and Pathological Correlations. Philadelphia, Pa: Lea and Febiger; 1989.
  15. Morris JM, Lane JI, Witte RJ, Thompson DM. Giant cell reparative granuloma of the nasal cavity. AJNR Am J Neuroradiol. 2004 Aug. 25(7):1263-5. [View Abstract]
  16. Thomas JE, Baker HL Jr. Assessment of roentgenographic lucencies of the skull: a systematic approach. Neurology. 1975 Feb. 25(2):99-106. [View Abstract]
  17. Unni KK. 5th ed. Dahlin's Bone Tumors: General Aspects and Data on 11,087 Cases. Philadelphia, Pa: Lippincott Williams & Wilkins; 1996.
  18. Youmans JR. 5th ed. Neurological Surgery. Philadelphia, Pa: WB Saunders Company; 2004. 3227-3268.

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.

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.