Imaging features of retroperitoneal and pelvic schwannomas

To describe the imaging features of retroperitoneal and pelvic schwannomas.

The presenting cross-sectional imaging for 18 sequential patients with retroperitoneal or pelvic schwannomas was reviewed retrospectively. Note was made of tumour diameter, position, homogeneity, margin, shape, calcification and invasion into adjacent structures. Where MRI had been performed, T1 and T2 signal intensity relative to skeletal muscle, and the degree and pattern of enhancement with gadolinium, were also assessed.

Imaging from 13 patients was available for review. The mean tumour diameter was 8.7 cm (range 4 to 15 cm); 9 schwannomas were located in the pelvis and 4 in the retroperitoneum; 12 cases showed smooth, regular margins and 1 case irregular, invasive margins. The tumours were homogeneous in 5 cases and heterogeneous with cystic change in 8; in 2 cases there was smooth expansion of a sacral nerve root exit foramen, and in 1 there was bony destruction of the sacrum and extension of tumour into the spinal canal. In 5 cases MRI was performed; on T1-weighted images all tumours were isointense; on T2-weighted images 4 tumours were hyperintense and 1 was isointense to skeletal muscle. In all cases the diagnosis was confirmed by core biopsy.

Retroperitoneal and pelvic schwannomas typically form large, well-circumscribed masses in the retroperitoneum or presacral area, and frequently undergo cystic degeneration. They can occasionally cause bony changes in the spine, but otherwise do not invade or obstruct adjacent structures. Although they are rare, it is important for the radiologist to recognize the typical appearance of schwannomas because they can be mistaken for malignant tumours.