Retroperitoneal schwannoma is a benign neurogenic tumor arising from Schwann cells of the peripheral nerve sheath. 0.5-5% of all schwannomas are retroperitoneal. Typically occurs in ages 20-50 with equal gender distribution. Usually slow-growing, well-defined, encapsulated masses. Appears on CT as a heterogeneously enhancing, well-defined solid-cystic mass. On T2-weighted MRI shows characteristic 'target sign' — peripheral hyperintense and central hypointense area — highly typical for schwannoma. Cystic degeneration is seen in 60-70% of cases, reflecting degeneration of Antoni B (myxoid) regions. May be associated with NF2. S-100 protein positive, c-KIT negative. Surgical excision is curative and recurrence is extremely rare.
Age Range
20-65
Peak Age
45
Gender
Female predominant
Prevalence
Uncommon
Schwannoma arises from Schwann cells in the peripheral nerve sheath. Retroperitoneal schwannomas usually originate from the sympathetic chain, intercostal nerves, or lumbar plexus branches. Histologically consists of two regions: Antoni A (compact, spindle cells, Verocay bodies) and Antoni B (loose, myxoid stroma). This bimorphological structure forms the basis of the 'target sign' on MRI — Antoni A central hypointensity (compact, low water), Antoni B peripheral hyperintensity (myxoid, high water). Cystic degeneration occurs from advanced myxoid degeneration of Antoni B regions and is common in large retroperitoneal schwannomas. The tumor capsule is perineurium-derived and facilitates separation from the nerve during surgery. Heterogeneous enhancement on CT reflects the difference between Antoni A's vascular structure and Antoni B's hypovascular structure. S-100 positivity confirms Schwann cell origin and distinguishes from GIST (c-KIT positive) and leiomyoma.
Target-like appearance of schwannoma on T2-weighted MRI with peripheral hyperintense halo (Antoni B myxoid) and central hypointense area (Antoni A compact). This bimorphological pattern is considered pathognomonic for schwannoma.
Characteristic 'target sign' on T2-weighted images: peripheral high signal halo (Antoni B — myxoid, high water content) and central low signal area (Antoni A — compact, low water content). In large lesions, cystic degeneration areas show very bright T2 signal. Capsule is seen as a thin hypointense ring on T2.
Report Sentence
The retroperitoneal mass shows 'target sign' on T2-weighted sequence with peripheral hyperintense halo and central hypointense area; consistent with schwannoma.
Well-defined, encapsulated, heterogeneously enhancing retroperitoneal mass on CT. Solid component (Antoni A) shows moderate enhancement while cystic/myxoid areas (Antoni B degeneration) do not enhance. Capsule is seen as a thin, smooth-contoured enhancing ring. Calcification is rare, hemorrhage foci may be seen in large lesions.
Report Sentence
A well-defined, encapsulated, heterogeneously enhancing solid-cystic mass is seen in the retroperitoneal space; cystic degeneration areas are prominent — consistent with schwannoma.
On T1-weighted images, the mass shows isointense or mildly hypointense signal to muscle. Intralesional hemorrhage areas may show focal T1 hyperintensity. Post-contrast T1 shows enhancement of solid component while cystic areas do not enhance — heterogeneous enhancement pattern.
Report Sentence
The mass shows isointense-hypointense signal on T1-weighted sequence with solid component enhancement post-contrast.
Well-defined, homogeneous or heterogeneous, low to soft tissue density (20-40 HU) mass in the retroperitoneal space on non-contrast CT. Cystic degeneration areas at water density (0-20 HU). Calcification is rare. Paravertebral or para-aortic location is typical.
Report Sentence
A well-defined, low density, solid-cystic mass is seen in the retroperitoneal space; paravertebral location is evaluated in favor of neurogenic tumor.
On DWI, solid component may show mild to moderate diffusion restriction; cystic degeneration areas show no diffusion restriction. ADC values are heterogeneous — solid areas show intermediate ADC, cystic areas show high ADC.
Report Sentence
The mass shows mild diffusion restriction in the solid component on DWI with free cystic areas; heterogeneous ADC pattern is consistent with schwannoma.
On US, a well-defined, heterogeneous hypoechoic, encapsulated solid-cystic mass. Cystic degeneration areas appear as anechoic regions. Posterior acoustic enhancement may be seen due to cystic component. Minimal vascularity on Doppler.
Report Sentence
A well-defined, heterogeneous hypoechoic, encapsulated solid-cystic mass is seen in the retroperitoneal space; consistent with neurogenic tumor.
Criteria
Most common type. Prominent Antoni A and B regions. Typical target sign on MRI. May have cystic degeneration. S-100 diffusely positive.
Distinct Features
Solid-cystic structure on CT/MRI, target sign, well-defined, encapsulated.
Criteria
Long-standing, slow-growing schwannoma. Advanced cystic degeneration, hemorrhage, calcification, hyalinization. May have heterogeneous, calcified areas on CT.
Distinct Features
Calcification and prominent cystic component on CT; heterogeneous signal on MRI, hemorrhage foci; may be confused with malignancy.
Criteria
Antoni A predominant, compact cellular structure. Less cystic degeneration. More homogeneous enhancement. Low mitotic activity, benign course but differential diagnosis with MPNST is important.
Distinct Features
More homogeneous T2 signal on MRI (reduced target sign), more solid structure, more homogeneous enhancement on CT.
Distinguishing Feature
Paraganglioma shows light bulb sign (very bright T2), salt and pepper pattern and prominent hypervascularity; schwannoma shows target sign and is less vascular.
Distinguishing Feature
Neurofibroma is diffusely associated with the nerve and cannot be separated; schwannoma is eccentrically located, encapsulated, and can be separated from the nerve. NF1 is associated with neurofibroma, NF2 with schwannoma.
Distinguishing Feature
Lymphangioma is a thin-walled, multiloculate cystic lesion without solid component; schwannoma has solid-cystic structure with enhancement in solid component.
Distinguishing Feature
Leiomyosarcoma has irregular margins, shows invasion into surrounding tissue and no capsule; schwannoma is well-defined, encapsulated and shows no invasion. IHC: schwannoma S-100+/SMA-, leiomyosarcoma SMA+/S-100-.
Urgency
routineManagement
surgicalBiopsy
Not NeededFollow-up
12-monthRetroperitoneal schwannoma is a benign neurogenic tumor. Surgical excision is curative for symptomatic lesions; complete enucleation is usually possible due to encapsulated structure and recurrence is extremely rare (<5%). Conservative follow-up may be applied for asymptomatic small lesions. MPNST differential diagnosis is made by irregular margins, invasion, and rapid growth. Systemic evaluation is recommended in NF2 patients due to risk of multiple schwannomas.
Retroperitoneal schwannomas are benign tumors and surgical resection is curative. Malignant transformation is very rare. May be associated with NF2. Preoperative biopsy is generally not needed — imaging findings can be diagnostic. Recurrence is rare.