Pediatric Plexiform Neurofibroma

  • Etiology: Benign peripheral nerve sheath tumor consisting of heterogeneous mixture of Schwann cells and perineural cells and fibroblasts
  • Imaging:
    — Often involves nerve segments next to vertebral column
    — Nodular tumor
    — Multiple lesions along major nerves
    — Individual nodules may break through outer nerve sheath and extend into surrounding soft tissues
    — Often causes sphenoid wing erosion (dysplasia)
  • Imaging MRI:
    — Usually large with multilobulated appearance and diffuse thickening of involved nerve and branches
    — T1WI: Hypointense
    — T1WI post contrast: Variable enhancement
    — T2WI: Hyperintense
  • Imaging MRI signs:
    — Fasicular sign – Multiple small ring-like structures with peripheral high signal intensity which represents fasicular bundles on T2WI
    — Split fat sign – Lesion is surrounded by rim of fat
    — String sign – Entering and existing nerve roots are seen at both ends of lesion
    — Target sign – On T2WI see high signal intensity rim due to myxomatous tissue and low signal intensity center due to fibrocollagenous tissue, fibrocollagenous tissue will enhance with contrast
  • DDX:
    — Schwannoma: Rare in children, is sporadic or associated with neurofibromatosis Type 2, is more heterogenous in appearance than neurofibroma
    — Malignant peripheral nerve sheath tumor: On PET the higher the maximum SUV the more likely that it is tumor, MRI has loss of target sign and has irregular margins and internal bright T1 signal and irregular enhancement
  • Complications: Malignant degeneration into malignant peripheral nerve sheath tumor
  • Treatment:
  • Clinical:
    — Development begins early in childhood
    — Almost exclusively seen in neurofibromatosis Type 1 so is pathognomonic for neurofibromatosis type 1
  • Note: Neurofibroma most commonly found as solitary lesion and is therefore sporadic but if there are multiple neurofibromas and they are plexiform (extending along branches of a nerve) then they are due to neurofibromatosis Type 1

Radiology Cases of Plexiform Neurofibroma

CXR and CT of plexiform neurofibroma in neurofibromatois type 1
CXR PA shows a large soft tissue mass in the apex of the right lung which causes thinning of the right 1st-5th ribs posteriorly. CT without contrast of the chest shows multiple small nodules throughout the soft tissues of the chest wall.
Tomogram of plexiform neurofibroma causing painful scoliosis
Coronal conventional tomogram of the thoracic spine shows a soft tissue mass in the apex of the right lung causing scalloping of the right side of the upper thoracic vertebral bodies and a scoliosis convex left.
CXR and CT of malignant peripheral nerve sheath tumor in neurofibromatosis type 1
CXR PA and lateral shows a right apical thoracic mass with associated rib thinning that had rapidly increased in size in a short interval. Axial CT without contrast of the chest better defined the right apical mass and demonstrated multiple serpiginous nodules in the soft tissues of the right anterior chest wall.
CXR and MRI of neurofibromatosis type I
CXR shows a posterior mediastinal mass. Coronal and sagittal T1 MRI without contrast of the thoracic spine shows dural ectasia.

Clinical Cases of Plexiform Neurofibroma

Clinical image of neurofibromatosis type 1 with chest wall and arm plexiform neurofibromas
Clinical image shows extensive, large soft tissue masses involving the right arm and chest wall.

Surgery Cases of Plexiform Neurofibroma

Surgery image of malignant peripheral nerve sheath tumor
Surgical image through a right thoracotomy shows a large mass originating in the apex of the right chest. Normal lung can be seen in the upper right corner of the incision.

Histopathology Cases of Plexiform Neurofibroma

Histopathology image of malignant schwannoma within a plexiform neurofibroma
Histopathological image H&E stained section shows short fascicles comprised of spindle-shaped cells with a moderate amount of pleomorphism and scattered mitoses, with malignancy being defined by the number of mitotic figures which can be counted. Overall this was felt to represent a malignant schwannoma within a plexiform neurofibroma.