Neurofibroma¶

Definition¶

Neurofibroma is a benign nerve sheath tumor composed of a mixture of Schwann cells, fibroblasts, perineurial cells, and collagen. Unlike schwannomas, neurofibromas are intertwined with the nerve fibers and cannot be separated from the parent nerve during surgery. They are strongly associated with neurofibromatosis type 1 (NF1), particularly when multiple or plexiform.

Types¶

Solitary neurofibroma — May occur sporadically or in the setting of NF1
Plexiform neurofibroma — Virtually pathognomonic of NF1; grows along the length of a nerve, creating a diffuse, tortuous mass ("bag of worms" appearance)

Imaging Findings¶

MRI¶

T1-weighted — Low to intermediate signal
T2-weighted — High signal with a characteristic "target sign" — central low T2 signal (fibrous tissue) surrounded by peripheral high T2 signal. This sign is more reliably seen in neurofibromas than schwannomas.
Enhancement — Variable; may enhance homogeneously or show peripheral enhancement
Morphology — Fusiform, centered along the nerve root. May extend through the neural foramen (dumbbell configuration).
Plexiform — Multiple, tortuous, diffuse masses along nerve courses, creating the "bag of worms" appearance

CT¶

Fusiform, low-attenuation mass along the nerve root
Foraminal widening
Plexiform neurofibromas may cause extensive bony remodeling

Clinical Pearl

The target sign (central low T2 with peripheral high T2) is more consistently seen in neurofibromas than schwannomas, though it is not entirely specific. The critical clinical distinction is that neurofibromas are intertwined with the nerve and cannot be separated at surgery — the nerve must be sacrificed for complete excision. Schwannomas grow eccentrically from the nerve and can usually be dissected free.

NF1 Association¶

Multiple neurofibromas, particularly plexiform neurofibromas, are a hallmark of NF1. Malignant transformation to malignant peripheral nerve sheath tumor (MPNST) occurs in approximately 8–13% of NF1 patients. Features suggesting malignant transformation include rapid growth, new pain, size >5 cm, heterogeneous enhancement, and perilesional edema.

Key Points¶

Neurofibromas are intertwined with the nerve and cannot be separated at surgery
The target sign on T2 MRI is characteristic
Plexiform neurofibromas are pathognomonic of NF1
Risk of malignant transformation (MPNST) in NF1 patients (8–13%)
Distinguish from schwannoma — neurofibromas are fusiform and inseparable from the nerve

References¶

Messersmith L, Krauland K. Neurofibroma. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2023. Available from: https://www.ncbi.nlm.nih.gov/books/NBK539707/
Wang MX, Dillman JR, Guccione J, Habiba A, Maher M, Kamel S, et al. Neurofibromatosis from head to toe: what the radiologist needs to know. RadioGraphics. 2022;42(4):1123-1144.
Wasa J, Nishida Y, Tsukushi S, Shido Y, Sugiura H, Nakashima H, et al. MRI features in the differentiation of malignant peripheral nerve sheath tumors and neurofibromas. AJR Am J Roentgenol. 2010;194(6):1568-1574.
Kakkar C, Shetty CM, Koteshwara P, Bajpai S. Telltale signs of peripheral neurogenic tumors on magnetic resonance imaging. Indian J Radiol Imaging. 2015;25(4):453-458.
Fisher MJ, Blakeley JO, Weiss BD, Dombi E, Ahlawat S, Akshintala S, et al. Management of neurofibromatosis type 1-associated plexiform neurofibromas. Neuro Oncol. 2022;24(11):1827-1844.
Ahlawat S, Ly KI, Fayad LM, Fisher MJ, Lessing AJ, Berg DJ, et al. Imaging evaluation of plexiform neurofibromas in neurofibromatosis type 1: a survey-based assessment. Neurology. 2021;97(7 Suppl 1):S111-S119.
Spinal neurofibroma. Radiopaedia.org. Available from: https://radiopaedia.org/articles/spinal-neurofibroma