Head and Neck Surgery

Posts Tagged ‘Fibrous dysplasia’

BONY LESIONS OF THE SKULL

Posted by headnecksurgery on February 5, 2009

Some of the more common idiopathic bone lesions of the head and neck are discussed here. Although their radiographic appearance may be similar, they can be differentiated by a thorough history and physical examination and appropriate laboratory evaluation.

Fibrous Dysplasia

Fibrous dysplasia, a skeletal disorder wherein medullary bone is replaced by fibroosseous tissue, manifests itself in three clinical forms: monostotic fibrous dysplasia, polyostotic fibrous dysplasia, and Albright syndrome. Monostotic fibrous dysplasia, the term applied when the disease is confined to one bone, accounts for 75% to 80% of all cases. Polyostotic fibrous dysplasia, which accounts for 20% to 25% of patients, is applied when two or more bones are involved. If polyostotic fibrous dysplasia is associated with abnormal skin pigmentation, precocious puberty, and other nonskeletal diseases, it is called Albright syndrome, which accounts for 20% to 25% of all polyostotic fibrous dysplasia patients.

Fibrous dysplasia occurs almost exclusively before age 30. Polyostotic fibrous dysplasia and Albright syndrome tend to occur in the first decade, and monostotic fibrous dysplasia usually manifests in the second or third decade. The disease is usually quiescent after puberty. Polyostotic fibrous dysplasia has a 3:1 female predominance. Monostotic fibrous dysplasia occurs with equal frequency in both sexes.

Most (90%) patients with fibrous dysplasia are asymptomatic. When symptomatic, patients may have local swelling, pain, displaced teeth, or nerve-compression symptoms. The most commonly affected bones are the ribs and femur for monostotic fibrous dysplasia and the femur and tibia for polyostotic fibrous dysplasia.

About 25% of patients with fibrous dysplasia have head and neck involvement. The maxilla is the bone most often affected, followed by the mandible. Painless asymmetric swelling is common.

The typical radiographic finding is an expanded osseous lesion with a poorly defined margin covered by an eggshell-thin cortex. Fibrous dysplasia also may present radiographically as a pagetoid lesion or as a sclerotic lesion. It should be considered when the paranasal sinuses are involved if radiographic studies show a calcified, thick, enlarged sinus margin and a ground-glass appearance of the mass inside the sinus .

Histologically, the fibrous dysplasia lesion reveals marrow replaced by whorled spindle cells. One differentiating feature is the lack of “osteoblastic rimming,” in which osteoblasts rim the fibroosseous tissue.

The differential diagnosis for fibrous dysplasia often depends on the location and radiographic characteristic of the lesion. Although the fibrous dysplasia lesion may appear pagetoid radiographically, it can easily be differentiated clinically. When located along the sphenoid ridge, it may look radiographically like a meningioma. Fibrous dysplasia also may be difficult to differentiate from osteomyelitis, which may coexist with it. A recent report describes the presentation of fibrous dysplasia of the middle turbinate that resulted in chronic sinusitis and then progressed to a periorbital abscess. Osteosarcoma must always be considered, because 1 in 200 cases undergoes malignant degeneration. Biopsy should be performed if the diagnosis is in doubt or if malignant degeneration is suspected. Excision or curettage is indicated if the lesion interferes with function, progresses in deformity, or undergoes sarcomatous transformation. The primary goal is contouring to minimize deformity. Recurrence rates reach 20% to 30% with curettage.

In recent years, refinement in surgical instrumentation and craniofacial surgical techniques have made more aggressive nondisabling procedures possible. Complete excision and bone graft reconstruction is possible in some patients.

Ossifying Fibroma

Ossifying fibroma is similar to fibrous dysplasia, but its onset, on average, is 10 years later. Its radiographic appearance is homogeneously dense in head and neck locations, similar to the appearance of fibrous dysplasia. The ossifying fibroma is usually more discrete. Histologically, it resembles fibrous dysplasia, but osteoblastic rimming is present. Treatment consists of excision, and recurrence is rare.

Paget Disease

The demographics and clinical manifestations of Paget disease differ from those of fibrous dysplasia. Paget disease rarely occurs before age 40 and most often occurs between age 55 and 70. Most (90%) patients have polyostotic disease. The lumbosacral region is the area most frequently involved. Patients with Paget disease are often asymptomatic but are more commonly symptomatic than those with fibrous dysplasia. The classic symptoms are enlarging skull, dorsal kyphosis, and bowing of the legs. The most common symptom is bone pain. Other symptoms that occur as complications of the disease include spinal root compression, normal pressure hydrocephalus, and repeated fractures with nonunion.

The classic radiographic findings of Paget disease follow the underlying histologic process. Initially, there is a lytic phase associated with increased osteoclastic activity with replacement with vascular stroma, followed by a mixed phase, with increased osteoblastic activity in addition to the osteoclastic activity, resulting in a mosaic pattern of bone. This produces the typical “cotton wool” appearance on the radiograph. During the final phase, the osteoblastic activity is preeminent. The radiographic picture becomes one of sclerosis.

Calcium and parathyroid hormone levels may be elevated secondary to the increased bone turnover, but they are usually normal. Patients with Paget disease often have elevated alkaline phosphatase levels secondary to increased osteoblastic activity and increased urinary hydroxyproline levels secondary to increased osteoclastic activity.

In the head and neck, Paget disease occurs more commonly in the skull than in the face, as seen in fibrous dysplasia. The skull is the third most often involved bone. Here lesions are typically lytic (i.e., osteoporosis circumscripta) and only slowly progress to the mixed phase. Paget disease of the jaw rarely occurs before age 40 and is usually bilateral. In contrast, fibrous dysplasia is usually unilateral and is rare after age 30.

The differential diagnosis for Paget disease includes fibrous dysplasia, osteomyelitis (which can coexist with it), osteitis fibrosa from primary hyperparathyroidism, and osteosarcoma. Like fibrous dysplasia, Paget disease can undergo malignant transformation. Between 1% and 5% of cases degenerate to an osteosarcoma; the 5-year survival rate is lower than other osteosarcomas. More rarely, Paget disease degenerates to giant cell tumor, which typically involves the skull and is less aggressive than other giant cell tumors, which rarely involve the skull and are seen almost exclusively in the long bones.

Usually, the clinical picture is classic, but a biopsy may help if the diagnosis is in doubt. The patient with Paget disease is also at risk of developing serious sequelae, including hypercalcemia, polycythemia, neurologic compression, malignant transformation, and congestive heart failure. These patients need close follow-up. Medical treatment becomes necessary when there is impending hypercalcemia, repeated fractures and nonunion, compression of nerves, and intractable bone pain.

Calcitonin is the drug of choice. It decreases bone turnover and alkaline phosphatase levels, urinary hydroxyproline, and the risk for heart failure. Disodium etidronate, which interferes with bone resorption and formation, is especially useful in treating intractable bone pain. Mithramycin is reserved for resistant cases because it is associated with severe side effects.

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