Neurofibromatosis type 1: A diagnostic mimicker at CT

Neurofibromatosis type 1 (NF1) is the most common of the phakomatoses and h as a variety of localized or, more frequently, systemic manifestations thro ughout the thorax, abdomen, pelvis, and extremities. Classic computed tomog raphic (CT) findings in NF I with thoracic involvement include small, well- defined subcutaneous neurofibromas, focal thoracic scoliosis, posterior ver tebral scalloping, enlarged neural foramina, and characteristic rib abnorma lities due to bone dysplasia or erosion from adjacent neurofibromas. Howeve r, more atypical manifestations are occasionally seen, and magnetic resonan ce (MR) imaging can be useful in equivocal cases. NF1 with abdominopelvic i nvolvement tends to arise in the retroperitoneal, mesenteric, and paraspina l regions; it may be quite extensive and therefore difficult to distinguish from adenopathy at CT. The multiplanar capabilities of MR imaging, particu larly with T2 weighting, make this modality helpful in evaluating affected patients and making the diagnosis. The classic peripheral manifestations of NF1 include limb hemihypertrophy, pseudarthrosis, peripheral nerve neurofi bromas, and subcutaneous common and plexiform neurofibromas. In some cases of NF1, imaging findings are inconclusive, and biopsy and subsequent pathol ogic analysis are required. Familiarity with the various manifestations of NF1 in different anatomic locations is important in making the diagnosis an d optimizing postdiagnostic treatment.