History
May is a 10 year female spayed French Bulldog with a history of hindlimb paresis. May has a history of cutaneous masses, but the referring veterinarian was concerned with a ~4-5cm firm, poorly defined mass in the left coxofemoral region. The referring veterinarian requested an MRI exam to rule out lipoma entrapped within the fascial planes, soft tissue sarcoma, or other mass.
Imaging Findings
At Animal Imaging, May was placed under general anesthesia and multiplanar MR images were acquired. May was found to have the left sciatic nerve at the level of L7-S1 asymmetrically enlarged and strongly contrast enhancing. As the sciatic nerve tracked caudodorsally adjacent to the left sacroiliac joint, it was contiguous with a markedly large (5.2cm W x 4.7cm L, 4.6cm H), lobular mass with peripheral rim contrast enhancement. This mass extended caudally to the level of the left coxofemoral joint and ischium, with pelvic canal extension, compression, and rightward deviation of the rectum.
Conclusion
May was found to have a large left sciatic nerve mass surrounding the left ilium, most consistent with neoplasia such as peripheral nerve sheath tumor. Other differentials include sarcoma with associated nerve extension or neuritis, round cell neoplasm, or less likely fungal granuloma. Secondary focal ilial osseous invasion and/or pressure necrosis and osteitis, and neurogenic atrophy of the left gluteal and proximal thigh musculature was also present.
Peripheral nerve sheath tumors (PNSTs) can be benign or malignant, while malignant varieties tend to stay locally aggressive and do not metastasize through the lymphatic system. These tumors arise from the protective sheaths that encapsulate nerves. Commonly PNSTs cause pain and therefore lameness in the forelimbs or hindlimbs, followed by muscle atrophy and monoparesis. PNSTs can occasionally compress the spinal cord and cause other limbs to become lame.
Surgical excision of the tumor depending on the location can be curative, but recurrence at the root of the nerve is common. Amputation may be elected in the mass is large enough. Because of the common recurrence, malignant peripheral nerve sheath tumors have a guarded prognosis.
