Mediastinal neurofibroma is a benign tumor originating from the peripheral nerve sheath and is one of the most common masses of the posterior mediastinum. It has a heterogeneous structure consisting of Schwann cells, fibroblasts, perineural cells, and myxoid matrix. Unlike schwannoma, it incorporates nerve fibers within it (intraneural growth — nerve passes through tumor and cannot be separated). It accounts for approximately 30-40% of all mediastinal neurogenic tumors. It can occur at any age but is most common between 20-40 years. There is a strong association with NF1 (neurofibromatosis type 1, von Recklinghausen disease) — multiple and bilateral neurofibromas are common in NF1 patients. Plexiform neurofibroma is pathognomonic for NF1. On CT, it appears as a well-circumscribed, low-to-intermediate density (20-30 HU), minimally enhancing mass in the posterior mediastinum. The target sign on T2-weighted MRI is pathognomonic: central hypointense fibrous core, peripheral hyperintense myxoid tissue. Spinal canal extension (dumbbell tumor) is a critical surgical planning finding. Risk of malignant transformation (MPNST) is approximately 8-13% (especially in plexiform neurofibromas in NF1); rapid growth and increasing pain are warning signs.
Age Range
20-50
Peak Age
30
Gender
Equal
Prevalence
Uncommon
Neurofibroma is a heterogeneous tumor originating from all components of the peripheral nerve (Schwann cells, fibroblasts, perineural cells, axonal elements) — this distinguishes it from schwannoma which consists only of Schwann cells. Mutation in the NF1 gene (chromosome 17q11.2) leads to loss of neurofibromin protein. Neurofibromin is a tumor suppressor that inhibits RAS-GTPase activation — its loss causes uncontrolled activation of the RAS/MAPK signaling pathway and cell proliferation. The tumor's myxoid matrix content explains the marked hyperintensity on T2-weighted images — free water molecules within myxoid tissue show long T2 relaxation. The target sign results from the contrast difference between central fibrous tissue (short T2 → hypointense) and peripheral myxoid tissue (long T2 → hyperintense). Posterior mediastinal location reflects origin from intercostal nerves and sympathetic chain. Dumbbell configuration indicates extension through neural foramen. Low CT density (20-30 HU) reflects high myxoid and collagen content.
Central hypointense (fibrous), peripheral hyperintense (myxoid) concentric pattern on T2-weighted MRI is pathognomonic for neurofibroma. Distinguishes from schwannoma.
Characteristic target sign pattern of neurofibroma on T2-weighted images: center of tumor is hypointense (fibrous/collagen tissue), periphery is hyperintense (myxoid/mucinous material). Best evaluated on axial sections creating circular target-like appearance. Target sign is pathognomonic for neurofibroma and distinguishes from schwannoma. In plexiform neurofibroma, multiple nodules with target sign along nerve pathways ('bag of worms' appearance).
Report Sentence
Mass in the posterior mediastinum demonstrating central hypointense, peripheral hyperintense target sign on T2-weighted images; consistent with neurofibroma.
On contrast-enhanced CT, well-circumscribed, low-density (20-30 HU), homogeneous or mildly heterogeneous, minimally enhancing mass in the posterior mediastinum. This low density reflects high myxoid and collagen content. Enhancement is minimal or absent — reflecting low tumor vascularity. Small neurofibromas (<3 cm) usually enhance homogeneously. Mass is paravertebral, may localize in costovertebral sulcus.
Report Sentence
Low-density (__ HU), well-circumscribed, minimally enhancing paravertebral mass in the posterior mediastinum; consistent with neurogenic tumor (neurofibroma).
On bone window CT, ipsilateral neural foramen widening and/or erosion of adjacent vertebral pedicles may be detected. This suggests the tumor originates from nerve root and extends into spinal canal (dumbbell configuration). Neural foramen widening reflects chronic pressure/erosion effect of a slowly growing lesion. Bilateral and multi-level foramen widening suggests NF1. Dumbbell configuration is critical for surgical approach planning — may require combined thoracic and neurosurgical approach.
Report Sentence
Ipsilateral neural foramen widening is observed; MRI evaluation is recommended for dumbbell configuration assessment.
On T1-weighted images, neurofibroma shows homogeneous signal isointense or mildly hypointense to muscle. Mild hypointensity may be seen due to myxoid component. Post-gadolinium smooth homogeneous or mildly heterogeneous enhancement — enhancement is minimal to moderate. Central component of target sign also shows low signal on T1.
Report Sentence
The lesion shows signal isointense to muscle on T1-weighted sequences with homogeneous minimal enhancement post-gadolinium.
MRI clearly evaluates tumor extension into the spinal canal through neural foramen (dumbbell configuration). Intraforaminal and intraspinal components are visualized with extraforaminal (mediastinal) component on coronal/sagittal sections. Hyperintense tumor tissue clearly separated from spinal cord on T2. Spinal cord compression degree and intraspinal tumor size directly assessed.
Report Sentence
The mass extends into the spinal canal through the neural foramen forming a dumbbell configuration; neurosurgical consultation is recommended.
Diffuse growth along nerve plexuses in plexiform neurofibroma: multiple, confluent, low-density nodular lesions. 'Bag of worms' appearance. Pathognomonic for NF1. May coexist with subcutaneous and deep soft tissue neurofibromas. Each nodule shows low attenuation due to myxoid matrix.
Report Sentence
Multiple low-density nodular lesions with diffuse growth along nerve plexuses, consistent with plexiform neurofibroma; NF1 should be evaluated.
Criteria
Single, well-defined mass; may be sporadic or NF1-associated
Distinct Features
Most common form. Fusiform or globular mass. Low malignant transformation risk (1-5%). Surgical excision curative but nerve preservation difficult due to intraneural growth.
Criteria
Diffuse growth along nerve plexuses; pathognomonic for NF1
Distinct Features
Bag of worms appearance. Diffuse, infiltrative. Highest MPNST transformation risk (8-13%). Surgical resection usually incomplete.
Criteria
Malignant transformation from neurofibroma; 8-13% risk in NF1 patients
Distinct Features
Rapid growth and pain are warning signs. Heterogeneous enhancement, necrosis, irregular borders on CT/MRI. High FDG on PET-CT (SUVmax >3.5-4). Size >5 cm increases risk. Marked diffusion restriction on DWI (low ADC).
Distinguishing Feature
Schwannoma consists only of Schwann cells; shows homogeneous T2 hyperintensity or Antoni A/B zonation — target sign not seen. Schwannoma grows eccentrically (nerve displaced), neurofibroma grows intraneurally. Schwannoma enhances more intensely. Associated with NF2 (neurofibroma with NF1).
Distinguishing Feature
Ganglioneuroma forms more homogeneous, elongated mass extending along multiple vertebrae. Calcification more common (20-30%). Neurofibroma usually more round/fusiform and better circumscribed.
Distinguishing Feature
Bronchogenic cyst in middle mediastinum (subcarinal), cystic, markedly T2 hyperintense. Neurofibroma in posterior mediastinum, solid, shows target sign.
Distinguishing Feature
Lymphoma usually anterior mediastinum with denser enhancement and widespread lymphadenopathy. B symptoms suggest lymphoma. Neurofibroma is isolated posterior mediastinal mass, low density.
Urgency
routineManagement
surgicalBiopsy
Not NeededFollow-up
6-monthMediastinal neurofibroma usually follows a benign course but requires careful follow-up in NF1-associated cases due to MPNST risk (8-13%). Neurosurgical consultation mandatory if dumbbell configuration. Small asymptomatic lesions can be followed (6-12 month MRI). Surgery for symptomatic or growing lesions. NF1 evaluation should include cafe-au-lait spots, Lisch nodules, genetic counseling. Rapid growth, pain increase, high FDG on PET-CT (SUVmax >3.5-4), or marked DWI restriction (low ADC) suggest MPNST — urgent biopsy needed.
Neurofibroma is a benign tumor but carries a 5-10% risk of malignant transformation to MPNST in the setting of NF1. Rapid growth, increasing pain, and diffusion restriction raise suspicion for malignant transformation. Genetic evaluation for NF1 is recommended in the presence of multiple neurofibromas.