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Craniotubular Dysplasias

by David D. Sherry, MD, Frank Pessler, MD, PhD

Craniotubular dysplasias are osteopetroses that involve minor osteosclerosis with normal skeletal modeling.

Metaphyseal dysplasia (Pyle disease)

This rare, autosomal recessive disorder is often confused semantically with craniometaphyseal dysplasia. Affected people are clinically normal, apart from genu valgum, although scoliosis and bone fragility occasionally occur.

The diagnosis is usually made when x-rays are done for an unrelated reason. X-ray changes are striking. Long bones are undermodeled, and bony cortices are generally thin. Tubular leg bones have gross Erlenmeyer flask flaring, particularly in the distal femur. Pelvic bones and thoracic cage are expanded. However, the skull is esentially spared.

Treatment is often not necessary but may involve orthodontic treatments for dental malformations or orthopedic surgery for clinically significant skeletal deformities.

Craniometaphyseal dysplasia

This autosomal dominant disorder is caused by mutations in the ankylosis, human ( ANKH) gene. Paranasal bossing develops during infancy, and progressive expansion and thickening of the skull and mandible distort the jaw and face. The encroaching bone entraps cranial nerves, causing dysfunction. Malocclusion of the teeth may be troublesome; partial sinus obliteration predisposes to recurrent nasorespiratory infection. Height and general health are normal, but progressive elevation of intracranial pressure is a rare, serious complication.

Diagnosis is suspected by typical craniofacial abnormalities, which are at times coupled with increased susceptibility to URI, or the disorder may be found during an evaluation for cranial nerve dysfunction that may result from entrapment at the skull base. Typically, plain x-rays are done. X-ray changes are age-related and usually evident by age 5 yr. Sclerosis is the main feature in the skull. Long bones have widened metaphyses, appearing club-shaped, particularly at the distal femur. However, these changes are much less severe than those in Pyle disease. The spine and pelvis are unaffected.

Treatment consists of surgical decompression of entrapped nerves and remodeling of severe bony abnormalities; however, regrowth does occur.

Frontometaphyseal dysplasia

This disorder has distinct autosomal dominant and X-linked forms; it becomes evident during early childhood. The supraorbital ridge is prominent, resembling a knight’s visor. The mandible is hypoplastic with anterior constriction; dental anomalies are common. Deafness develops during adulthood because sclerosis narrows the internal acoustic foramina and middle ear or may cause deformities of the ossicles. Long leg bones are moderately bowed. Progressive contractures in the digits may simulate arthritis. Height and general health are normal.

Diagnosis is suspected by hearing loss in a patient with features of the skeletal abnormalities described previously. Typically, plain x-rays are done. On x-ray examination, bony overgrowth of the frontal region is obvious; patchy sclerosis is seen in the cranial vault. Vertebral bodies are dysplastic but not sclerotic. Iliac crests are abruptly flared, and pelvic inlet is distorted. Femoral capital epiphyses are flattened, with expansion of the femoral heads and coxa valga (hip deformity). Finger bones are undermodeled, with erosion and loss of joint space.

Corrective surgery is indicated for severely disfiguring deformities, including severe micrognathia, or those causing orthopedic problems. Hearing loss is treated with hearing aids.

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