Over the course of their lifetime, patients with NF1 are at inherently greater risk for developing malignancy as compared with the general population. Some examples of neoplasms seen more frequently in NF1 patients include leukemia, rhabdomyosarcoma, pheochromocytoma, Wilms tumor, pancreatic endocrine tumors, and astrocytic-origin brain tumors.

BONE LESIONS

Deformity of Spine. Scoliosis is the most common bone lesion in neurofibromatosis, historically being reported in as high as 60% of NF1 patients who present to the orthopaedic surgeon. The true incidence over the general NF1 population is likely closer to 10%. Two patterns of scoliotic deformity have been identified. The deformity can vary from mild, nonprogressive forms (nondystrophic) to the less common (but more severe) form with tight, short curves (dystrophic) (see Plate 4-22). The cervical spine should also be monitored, because NF1 patients can have cervical kyphosis, rotary subluxation, and atlantoaxial instability develop.

Type I spinal deformity (dystrophic curves) are characterized by multiple abnormalities, such as foraminal enlargement, vertebral scalloping, “penciling” of ribs/transverse processes, dural ectasia (dural thinning), pedicle dysplasia, interpediculate distance widening, severe apical rotation, paravertebral soft tissue mass, and “grotesque” hairpin curves resulting in thoracic kyphoscoliosis, most commonly. This type of scoliosis tends to be progressive and to resist stabilization of the spine with the usual methods. CT and MRI are needed to rule out congenital deformity, dysplasia, and intradural pathologic processes and are necessary for preoperative planning.

The classic NF1 dystrophic curve is further divided into two subtypes: lateral curve (scoliosis) and anterior curve (kyphoscoliosis), in which the kyphotic element (>50 degrees) predominates over the scoliotic element. The kyphotic type of spinal deformity is believed to contribute more to paraplegia than the lateral deformity. Flexion of the spine causes elongation of the vertebral canal and plastic deformation of the spinal cord. Increased spinal flexion due to the kyphotic deformity increases axial tension in the spinal cord parenchyma, resulting in functional neurologic impairment or paraplegia. This type of deformity is not successfully treated with routine posterior spinal fusion because it tends to result in pseudarthrosis. Spinal fusion with both anterior and posterior approaches is needed to prevent progression of the deformity (“crankshaft” phenomenon) and decrease the risk of pseudarthrosis.

Type II spinal deformity appears to be indistinguishable from idiopathic scoliosis and is an incidental finding in patients with neurofibromatosis. Follow-up studies of patients with type II deformity show less progression of the curve and better response to treatment. Despite a less severe curve pattern, careful serial examination for type II curves is essential, with as many as 65% of patients developing dystrophic changes. In contrast to idiopathic scoliosis, the incidence of pseudarthrosis in the spine tends to be higher than in NF1 scoliosis patterns.