Axial T2-W image in a child with neurofibromatosis type 1, s | Figure 1

CincyKidsRad

Cincinnati Children's Radiology

Axial T2-W image in a child with neurofibromatosis type 1, shows a large plexiform neurofibroma of the pelvis. The plexiform neurofibroma is composed of multiple lesions, each with a characteristic target appearance. The target appearance occurs because the neurofibroma contains a central area of dense collagen. The target sign is not always present in plexiform neurofibromas. However, if a tumor loses the sign, this is considered to be a finding of degeneration to a malignant peripheral nerve sheath tumor. Other findings of malignant degeneration include heterogeneous enhancement, lobulation of the tumor, and rapid change in size, and irregular margins.

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This patient has Neurofibromatosis type 1 (NF 1) with extensive lumbar and sacral neurofibromas extending through the neural foramina and into the adjacent paraspinal soft tissues. Optic pathway gliomas are an associated orbital feature, as are plexiform neurofibromas involving the orbit, Lisch nodules (iris hamartomas), buphthalmos or large globes, and tortuosity and ectasia of the optic nerve sheaths. Skin findings in NF 1 may include café au lait spots (hyperpigmented lesions) and inguinal and axillary freckling.

Coronal T2 weighted image from a whole body MRI (image 1) shows extensive plexiform neurofibromas involving the upper extremities. Post contrast T1 weighted MRI (image 2) shows a focal area of enhancement (arrow) of one portion of the plexiform neurofibroma concerning for degeneration to a malignant peripheral nerve sheath tumor. PET/CT (image 3) highlights FDG uptake (arrow) within the small tumor. Malignant peripheral nerve sheath tumor is a type of sarcoma. 50 to 60% of patients with malignant peripheral nerve sheath tumor have neurofibromatosis type I.

Axial T1-weighted (image 1) and axial T1-weighted postcontrast (image 2) MR images highlighting the malignant peripheral nerve sheath tumor (arrow). MRI features that can be used to help differentiate a malignant peripheral nerve sheath tumor from a plexiform neurofibroma include loss of a target appearance on T2-weighted images, inherent T1 hyperintense signal, and heterogeneous enhancement.

Frontal chest radiograph in a patient with neurofibromatosis type I (NF1) shows a short angular upper thoracic dextroscoliosis. An adjacent soft tissue mass (white) and multiple dysplastic ribs are noted. Coronal T2-weighted MR image in the same patient with NF1 shows a predominantly hyperintense mass (white) infiltrating the soft tissues adjacent to the spinal curvature and the left chest wall. A “target” appearance (yellow) is seen within one component of the mass, typical of plexiform neurofibromas viewed in cross-section.