Malignant peripheral nerve sheath tumor (MPNST) is also known as neurofibrosarcoma, neurogenic sarcoma, malignant neurofibroma, and malignant neurilemmoma . About 3 – 13% of patients with neurofibromatosis-1, especially those who may have received radiotherapy, develop malignant transformation of a neurofibroma.Although the MRI features of benign and malignant neural tumors overlap, a large tumor size, irregular margins with invasiveness, and a heterogenous appearance are findings that suggest malignancy. The lack of a ‘target sign’ (a hyperintense rim with centrally decreased intensity on T2W images, seen in neurofibromas) indicates that the classic findings of a benign neuroma are absent and this may be suggestive of malignancy . On postcontrast imaging, malignant tumors predominantly show peripheral enhancement, with lack of central enhancement due to central necrosis and hemorrhage.The role of MRI in these tumors is vital, to resolve important preoperative questions about occult proximal intraneural spread, intradural extension, and anatomical relationship with the vertebral arteries
A 59-year-old male with neurofibrosarcoma involving the right brachial plexus. Coronal STIR (A) image shows a large heterogeneous, predominantly hyperintense, mass arising from the right brachial plexus (arrows). Focal linear low-signal septae are seen within. Contrast-enhanced, fat-suppressed, axial (B) image shows the mass enhancing intensely; it is dumbell-shaped, with a small intraspinal component that indents the thecal sac, and a large paravertebral component
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