eMedicine Specialties > Neurology > Neuro-oncology

Benign Skull Tumors

Author: Draga Jichici, MD, FRCP, Associate Clinical Professor, Department of Medicine, Division of Neurology and Critical Care Medicine, McMaster University, Canada
Contributor Information and Disclosures

Updated: Oct 13, 2009

Introduction

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 Rengachary¹⁵ (which is a modified version of the system outlined by Huvos⁹ ).

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^1,2,3

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.

Clinical

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,⁴ 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.
• Osteomas usually involve the frontal bone.
  • Ossifying fibromas favor the frontotemporal region.
  • Cartilage tumors involve the skull base.
  • Giant cell granuloma affects the sphenoid, temporal, and ethmoid areas.
  • Eosinophilic granuloma affects the frontoparietal area.
  • The globular variety of hemangiomas affects the skull base, and the sessile type affects the frontotemporal region.
  • Epidermoids and dermoids usually involve the cerebellopontine angle, parapituitary region, and calvaria. Dermoids prefer the midline.
  • Ossifying meningiomas involve the frontal parietal area.
  • Paget disease usually involves the skull base.

Physical

Physical findings vary according to tumor type.

• The lesion may be tender or nontender.
• It may be soft or hard.
• Cranial nerve deficits (eg, diplopia, hearing loss, vertigo, sensation loss) may be seen.

Causes

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

• Gardner syndrome is the triad of the following:
  • Multiple osteomas of the skull, sinus, and mandible
  • Soft tissue tumors of skin
  • Colon polyps
• McCune-Albright syndrome comprises the triad of the following:
  • Polyostotic fibrous dysplasia
  • Hyperpigmented skin macules
  • Precocious puberty
• Hand-Schüller-Christian disease consists of the following:
  • Diabetes insipidus
  • Exophthalmos
  • Bone lesions
• Multiple enchondromas is known as Ollier syndrome.
• Maffucci syndrome consists of the following:
  • Enchondromas
  • Dyschondroplasia
  • Cavernous hemangiomas of soft tissues or viscera

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