A 45-year-old female patient presented with non-specific symptoms of upper GI distress. Physical examination was unremarkable. Abdominal ultrasonography revealed absent right kidney and a 5.5x5 cm well-defined lesion in the right paraspinal region arising from the lumbar spinal nerve root. MRI abdomen, non -ontrast CT and F.N.A.C. confirmed the diagnosis.
Abdominal ultrasonography revealed absent right kidney and a 5.5x5 cm well-defined mixed heterogeneous lesion with internal vascularity in the right paraspinal region displacing the right psoas muscle anteriorly, suggesting a retroperitoneal location of the lesion (Fig. 1, 2). There was no evidence of internal calcification or necrotic areas. The lesion was seen arising from the exiting spinal nerve root at L3 vertebra identified by counting upwards from the lumbosacral angle (Fig. 3). CT scan of the abdomen showed a well-defined soft tissue density lesion in the right paraspinal space arising eccentrically from the exiting nerve root at L3 vertebra with no evidence of intraspinal extension of the lesion, confirming the ultrasound findings (Fig. 4, 5). The lesion was hypointense on T1 and heterogeneously hyperintense on T2-weighted images with moderate heterogeneous contrast enhancement and showed continuity with the exiting nerve root at L3 vertebra (Fig. 6). A presumptive diagnosis of neurogenic tumour was made and ultrasound-guided biopsy was done, which was diagnostic of schwannoma.
Primary tumours of the retroperitoneal region are quiet rare, and schwannomas comprise only 1–10% of them. Schwannomas originate from Schwann cells of the peripheral nerve fibres and are usually located in the head, neck, and flexor surfaces of the extremities. Schwannomas are quiet rare in the retroperitoneal region. Among all schwannomas, only 0.7% of the benign ones and 1.7% of the malignant ones are reported to be located in the retroperitoneal region. The majority of retroperitoneal schwannomas are benign in nature, although malignant ones have also been reported [1–3].
Schwannomas are usually seen in the adult population between the ages of 20 and 50. Symptomatology of benign schwannomas is highly nonspecific and depends on the location and size of the lesion. Retroperitoneal region is a rare location for schwannomas. In general, since the retroperitoneal space is rather large and flexible, the diagnosis of retroperitoneal schwannomas is often delayed, and the lesion reaches a significant size at the time of diagnosis. The most common symptoms are abdominal pain and distension. Schwannomas are located typically eccentric in relation to the nerve of origin. They often have a true capsule which is composed of epineurium. In general, schwannomas are seen as hypointense on T1 and hyperintense on T2-weighted MR images. These findings could be seen on imaging in our patient. The differential diagnosis for retroperitoneal tumours is vast, however, demonstrating continuity of the lesion with a peripheral nerve limits the differential to peripheral nerve sheath tumours, which include schwannoma, neurofibroma and malignant peripheral nerve sheath tumour.
Take home message:-
Retroperitoneal schwannoma is a rare tumour and it can be detected incidentally on ultrasonography.
Lesion characterization as a neurogenic tumour can be done if continuity with a peripheral nerve and internal vascularity is demonstrated.
MRI is regarded as the diagnostic modality of choice in the evaluation of retroperitoneal tumours.
Differential Diagnosis List
Lumbar spinal nerve root schwannoma
Malignant peripheral nerve sheath tumour
Lumbar spinal nerve root schwannoma