Mediastinal schwannoma is a benign neurogenic tumor originating from Schwann cells of the peripheral nerve sheath, most commonly located in the posterior mediastinum. It constitutes 12-21% of all mediastinal tumors and is the most common cause of posterior mediastinal masses. Typically develops from spinal nerve roots or intercostal nerves in the paravertebral sulcus. Usually slow-growing, asymptomatic masses discovered incidentally. Large tumors may cause pain due to intercostal nerve compression, neural foraminal widening, or intraspinal extension (dumbbell tumor). On CT, it appears as a well-defined, round-oval, posterior mediastinal mass. On MRI, the characteristic 'target sign' provides a diagnostic clue. Cystic degeneration is common in large tumors (66%). Treatment is surgical resection with low recurrence rate (<5%). Malignant transformation is rare (1-5%), with increased risk in NF2 syndrome-associated cases.
Age Range
25-55
Peak Age
40
Gender
Equal
Prevalence
Uncommon
Schwannoma originates from Schwann cells of the peripheral nerve sheath. Normal Schwann cells form the myelin sheath surrounding nerve axons; schwannoma is the neoplastic proliferation of these cells. Histologically, it contains two components: Antoni A areas (compact, spindle cells, palisading arrangement with Verocay bodies) and Antoni B areas (loose, myxoid stroma, low cellularity). These two components form the basis of the 'target sign' on MRI — peripheral T2 hyperintensity reflects myxoid Antoni B areas, while central low signal reflects compact Antoni A areas. The tumor grows in an encapsulated fashion, pushing nerve fibers aside — this feature differs from neurofibroma. Cystic degeneration is common in large tumors (66%) due to ischemic necrosis and hemorrhage, contributing to heterogeneous appearance on CT/MRI. Paravertebral location in the posterior mediastinum reflects the tumor's spinal nerve root or intercostal nerve origin. Neural foraminal widening results from the foraminal component slowly remodeling the foramen.
Combination of peripheral hyperintensity (myxoid Antoni B) and central low signal (compact Antoni A) on T2-weighted MRI — target-like concentric signal distribution reflecting histological structure of schwannoma.
On CT, a well-defined, round or oval, mildly heterogeneously enhancing mass is seen in the paravertebral sulcus. On non-contrast CT, isodense to muscle (30-40 HU). Mild to moderate enhancement after contrast (50-70 HU). Cystic degeneration areas appear as non-enhancing low-density foci.
Report Sentence
Well-defined, round, mildly heterogeneously enhancing mass in the paravertebral sulcus; neurogenic tumor (schwannoma) is primarily considered.
On T2-weighted MRI, schwannoma shows the characteristic 'target sign': peripheral hyperintense ring and central low-signal center. Peripheral hyperintensity reflects Antoni B areas with loose myxoid stroma and high free water content. Central low signal represents Antoni A areas with compact cellular arrangement. In the presence of cystic degeneration, the target sign may be disrupted.
Report Sentence
The posterior mediastinal mass demonstrates target sign with peripheral hyperintensity and central low signal on T2-weighted images; consistent with schwannoma.
On T1-weighted pre-contrast MRI, schwannoma shows isointense or mildly hypointense signal to muscle. Cystic degeneration shows low T1, hemorrhage may show high T1. Heterogeneous enhancement post-gadolinium — solid components enhance while cystic areas do not.
Report Sentence
The mass shows isointense signal to muscle on T1 with enhancement of solid component and no enhancement of cystic degeneration areas post-contrast.
Cystic degeneration is common in large schwannomas (66%), appearing as low-density areas (10-20 HU). It develops from ischemic necrosis with tumor growth. Cystic component may be dominant in some cases. On contrast-enhanced CT, cystic areas show no enhancement while solid component enhances.
Report Sentence
Low-density areas consistent with cystic degeneration are seen within the posterior mediastinal mass; consistent with a large schwannoma.
Neural foraminal widening is seen when schwannoma originates from spinal nerve root. On CT bone window, foraminal widening compared to contralateral side is detected. Intraspinal extension (dumbbell configuration) — one component in posterior mediastinum, another in spinal canal, connected through foramen. This finding strongly supports neurogenic origin and is critical for surgical planning.
Report Sentence
Neural foraminal widening adjacent to the posterior mediastinal mass with extension into the spinal canal (dumbbell configuration); consistent with schwannoma.
On DWI, schwannoma typically does not show marked diffusion restriction — ADC values higher than malignant tumors (>1.2 × 10⁻³ mm²/s). Solid component may show mild restriction. Marked restriction (ADC <0.8 × 10⁻³ mm²/s) raises MPNST suspicion.
Report Sentence
The posterior mediastinal mass does not show marked diffusion restriction on DWI, with ADC values consistent with benign neurogenic tumor.
Criteria
Most common subtype. Mixture of Antoni A and Antoni B areas. Well-defined, encapsulated, usually solitary. S-100 diffusely positive.
Distinct Features
Homogeneous or mildly heterogeneous enhancement. Cystic degeneration common. Surgical resection curative, recurrence <5%.
Criteria
Antoni A dominant, high cellularity, prominent Verocay bodies. Mitotic activity may be increased but not malignant. S-100 positive.
Distinct Features
More homogeneous enhancement, less cystic degeneration. May show slightly more diffusion restriction on DWI. Histological distinction from MPNST important.
Criteria
Bilobular configuration extending through neural foramen into both posterior mediastinum and spinal canal. Originates from spinal nerve root. Foraminal widening characteristic.
Distinct Features
Dumbbell configuration best evaluated on MRI sagittal/coronal images. Intraspinal component may cause spinal cord compression. Surgical approach must include both components.
Distinguishing Feature
Neurofibroma grows within the nerve, may show reverse target sign (central T2 hyperintensity). Associated with NF1. Higher malignant transformation risk (5-10%).
Distinguishing Feature
Ganglioneuroma is usually longer, oval-fusiform. Calcification more common on CT (40%). Less enhancement, more homogeneous. More common in children and young adults.
Distinguishing Feature
Paraganglioma shows intense hypervascular enhancement — different from schwannoma's mild-moderate enhancement. Biochemical evaluation required before biopsy. MRI 'salt-and-pepper' pattern and T2 'light bulb sign' are paraganglioma-specific.
Distinguishing Feature
Same histology but spinal/paraspinal localization. Posterior mediastinal paravertebral sulcus location is specifically distinguishing. Target sign can be seen in both locations.
Urgency
routineManagement
surgicalBiopsy
Not NeededFollow-up
12-monthMediastinal schwannoma is benign and surgical resection is curative. Preoperative biopsy is generally unnecessary with typical imaging findings. Multidisciplinary approach with neurosurgery is required for intraspinal extension. Periodic MRI follow-up (6-12 months) is an option for small asymptomatic lesions. Genetic counseling for NF2-associated cases. Malignant transformation risk is low (1-5%) — rapid growth, irregular margins, and marked diffusion restriction raise suspicion.
Schwannoma is a benign tumor and surgical resection is curative. The intraspinal component must be carefully assessed in dumbbell tumors. Malignant transformation (MPNST) is very rare. Association with NF2 is possible — NF2 should be investigated in bilateral or multiple schwannomas.