Discussion
Diagnosis With Brief Discussion
- Diagnosis
- Malignant Peripheral Nerve Sheath Tumor in Neurofibromatosis Type 1
- Radiologic Findings
- Contrast-enhanced CT scans show a well-defined mediastinal mass with areas of low attenuation. Multiple skin nodules are seen on lung-window image.
- Brief Review
- Neurofibromas are tumors derived from Schwann cells, fibroblasts, and supporting cells known as perineural cells. Typically, they are benign and manifest as multiple tumors. NF1 is an autosomal dominant genetic disorder with a prevalence of approximately 1 in 4,000 births and no racial predilection. NF1 is characterized by multiple neurofibromas along the peripheral nerves, optic nerve gliomas, sphenoid wing dysplasia, pigmented iris nodules, and hyperpigmented macular skin lesions known as caf?au-lait spots. It is associated with a gene on chromosome 17. The formation of dermal neurofibromas is a hallmark of NF1 with a characteristic distribution on the trunk and sparing of the extremities. With time, neurofibromas may undergo malignant degeneration. Malignant peripheral nerve sheath tumors (MPNSTs) most commonly occur in the deep soft tissues, usually close to a nerve trunk. The most common sites are the sciatic nerve, brachial plexus, and sacral plexus. The past literature referred to MPNST as malignant schwannoma, neurogenic sarcoma, and neurofibrosarcoma. Malignant peripheral nerve sheath tumor is the current term used by the World Health Organization for this highly aggressive tumor. MPNSTs may arise from plexiform neurofibromas, de novo or secondary to radiation therapy. At histologic analysis, the presence of mitotic figures distinguishes MPNST from otherwise typical neurofibromas. MPNST accounts for approximately 10% of soft-tissue sarcomas, and 40%?0% of MPNSTs arise from cases of NF1. Overall, there is a 4% chance of malignant transformation in NF1. Radiologically, MPNSTs and neurofibromas may appear indistinguishable; however, certain modalities are providing insight for differentiation. Gallium-67 citrate imaging has shown that MPNSTs have greater uptake compared with benign lesions. At magnetic resonance imaging, the different signal intensity characteristics of lesions with a higher degree of anaplasia are proving useful as well. Other factors such as a more rapid and infiltrative growth pattern are particularly helpful in distinguishing the two.
- References
- 1. Murphey MD, Smith WS, Smith SE, Kransdorf MJ, Temple HT. Imaging of musculoskeletal neurogenic tumors: radiologic-pathologic correlation. RadioGraphics 1999; 19:1253-1280.
2.Hrehorovich PA, Franke HR, Maximin S, Caracta P. Malignant peripheral nerve sheath tumor. RadioGraphics 2003; 23:790-794.
- Keywords
- Mediastinum, Malignant tumor,