Retroperitoneal Schwannoma: CEUS visualization and US-guided Core biopsy diagnosis

A 65-years old man, with no known oncologic risk factors or symptoms, incidentally found a retroperitoneal mass located in the left iliac region, during a Computed Tomography (CT). The mass, with a maximum diameter of 7 cm, was studied with CEUS-guided biopsy, which revealed a retroperitoneal Schwannoma.

CT scan reveals an ovalar mass with dimension 67x59x72mm (APxLLxCC); it relates dorsally and laterally with the iliacus muscle and medially with the psoas muscle from which it doesn’t appear clearly separated by a cleavage plane. The lesion appears to be enveloped entirely in a thin pseudocapsule demonstrating faint contrast enhancement. The content appears predominantly cystic with the exception of the most caudal portion. Positron Emission Tomography (PET) revealed important F-18-Deoxyglucose (18- FDG) captance, in particular in the caudal part of the lesion, and a lower intensity in lateral walls and the core.

Lastly, Contrast-Enhanced Ultrasound (CEUS) clearly showed a cystic ovalar lesion with fluid content, with multiple solid septa showing intense vascularization, the main target of our biopsy.

Retroperitoneal Schwannomas are slow-growing, benign soft tissue lesions, originating from Schwann cells. Predominantly involving head-neck, but also representing 3% of retroperitoneal tumours. The lesions are generally well-circumscribed, encapsulated, with variable density sometimes demonstrating inflammatory infiltration. Symptoms are usually aspecific and variable according to size and localization of the lesion. Most frequently the finding is incidental in asymptomatic patients or can be due to imaging performed for aspecific symptoms like abdominal or lumbar pain. [1]

US can reveal a solid or cystic abdominal mass, with non-specific features. CT scans normally reveal well-defined low or mixed-attenuation lesions with cystic or necrotic central areas. Cystic morphology is seen more commonly in retroperitoneal schwannomas than in other retroperitoneal tumours. [2]

Magnetic Resonance Imaging (MRI) can be used to show tumour’s origin, vascular architecture and involvement of other organs. T1 sequence reveals hyperdense or isodense lesion. [1]

Prognosis is good and recurrence is reported in 5-10% cases, probably due to incomplete excision. Despite their benign nature, it’s very important to include the lesion’s borders, evaluating eventual neurovascular structures involvement [1].

The focus of our article is to show that use of CEUS by allowing to more accurately characterize the vital vascularized, non-necrotic, parts of the mass can help in guiding core biopsy thus improving the sensitivity of the exam and allowing to perform a diagnosis.

In fact CEUS allows to discriminate the target area from the other adjacent structures exploiting the alterated vascularization of the tumour.

The procedure can be performed with a single contrast injection. Briefly, the vital areas of the lesion, rich in replicating cells, show strong enhancement and a better perfusion compared the necrotic areas which will appear anechogenic and non-enhancing.

These are some of the advantages afforded by CEUS in this setting:

• minimally invasive procedure;
• no radiations exposure;
• no need for nephrogenic contrast agents, the contrast is eliminated by respiration;
• real-time visualization of the needle, reduces complications and increases sensitivity. [3]

We believe CEUS can be used by multidisciplinary teams to achieve a diagnosis not only with open or video-assisted surgery, but also with these mini-invasive techniques which allow more accurate diagnostic procedures.

Written informed patient consent for publication has been obtained.