Pseudarthrosis in the context of NF1 has been reported to occur with lesser frequency in other long bone regions, such as the humerus, radius, ulna, and clavicle.

Tumors. Neurologic hamartomatous lesions in neurofibromatosis are uncommon but not rare (see Plate 4-23). A dumbbell tumor is a neurofibroma that arises in the vertebral canal and grows outward through the intervertebral (neural) foramen, its midportion being constricted by the bony foramen. Despite rare malignant transformation, retroperitoneal masses or dumbbell tumors that extend from the vertebral canal may cause mass-effect phenomena such as intestinal obstruction or neurologic compromise. Some tumors recur and overgrow into a vital area, rendering repeat excision impossible.

Bone Erosion. Erosive defects of bone in neurofibromatosis, which appear on radiographs as cysts, may be secondary to contiguous neurogenic tumors. Increased pressure in the dural sac may give rise to dural ectasia or pseudomeningocele in the vertebral canal. Thought to be a consequence of coinciding thecal sac pulsations and elevated intrathecal pressures, expansion of a thinned dural wall can cause bony erosion, widened interpedicular distances, and narrowed pedicle canals. Likewise, dumbbell tumors of the spinal cord cause enlargement of the intervertebral foramen as they exit the vertebral canal.