Dysplasia of the orbit and adjacent bone associated with plexiform neurofibroma and ocular disease in 42 NF-1 patients.

Neurofibromas are the hallmark of neurofibromatosis type 1 (NF1). Interestingly, generalised and localised interference or dysfunction of bone is also a key element of the NF1 phenotype. In the skull, NF1-associated orbital dysplasia often results in a severe disfigurement of affected individuals. However, the underlying pathology of orbital dysplasia is a complex phenomenon and up to now poorly understood. This study was performed to describe the orbit in 42 NF1 patients with large, disfiguring soft-tissue tumour of the orbital/eyelid region (plexiform neurofibroma (PNF)). A dysplastic orbit on the affected side was diagnosed in 80.9%. Orbital PNF extension to adjacent regions revealed a significant correlation of orbit and temporal region (0.33, p<0.034), cheek and oral cavity (0.4, p>0.011), oral cavity and nose (0.35, p<0.026), and temporal region and cheek (0.46, p<0.003). Alterations of the optic nerve and adjacent structures were identified on MRI or CT in 14 patients. On plain skull radiographs, only sphenoid wing dysplasia and ipsilateral orbital enlargement were significantly correlated (0.528, p<0.01). This study reveals PNF as the main component of soft tissue affecting eyelids and orbit in those cases, which show a soft tissue mass in the affected orbital region. The oval-shaped orbital rim, typically seen on plain skull radiographs in sagittal projections, seems to be strongly associated with the (lateral and caudal) extension of a PNF and independent from sphenoid wing dysplasia. Several factors constitute the individual orbital dysplasia, including the growth of the invasive PNF.