A large desmoids-type fibromatosis in left deep buttock and thigh

A 48-year-old man had a history of left lower limb pain and radiated to dorsalis pedis for 5 years with the left buttock muscle progressively experiencing atrophy. The patient had difficulties in walking. Pelvic X-ray examination and lumbar intervertebral disc CT images showed no obvious abnormality. CT scan from hip to knee demonstrated a solid mass deep in muscular spatium adjacent to gluteus maximus and distributed along the sciatic nerve (Figure 1). The MPR coronal images showed the neoplasm was as long as 40 cm with an irregular or partially lobulated contour and locally ill-defined border (Figure 2). Sagittal CT demonstrated the density of tumor is similar or slightly higher than skeletal muscle (Figure 3). On MR images, the tumor showed uneven signals in both T1W images and T2W images, mainly hyperintense to skeletal muscle and with stripe or patch-like markedly low signal which represented dense collagen in histology (Figure 4, 5, 6, 7). After contrast injection, the mass showed moderate to severe heterogeneous enhancement (Figure 5). The partially resected mass was tough, lobulated and showed hemorrhage in macroscopic section (Figure 6). Microscopically, the tumor was composed of spindle cells and collagen bundles, with a variable amount of collagen surrounding the spindle cells. Mitoses were present in the tumor cells but nuclear atypia was not seen (Figure 7).

Figure 1 Axial CT shows the solid mass deep in muscular spatium adjacent to gluteus maximus and can not be separated from the sciatic nerve

Figure 2 MPR coronal image shows the mass takes a wide longitudinal distribution with an irregular or partially lobulated contour and locally ill-defined border

Figure 3 Sagittal CT demonstrates the density of mass is equal or slightly higher than skeletal muscle

Figure 4 In both T₁W image (A) and T₂W image (B), the mass shows heterogeneous mixed hyperintense and hypointense signals, with stripe or patch-like markedly low signal

Figure 5 After contrast injection, the mass showed moderate to substantial heterogeneous enhancement

Figure 6 The partially resected mass is tough, lobulated, and parts of the area have hemorrhage

Figure 7 Microscopically, the tumor is composed of spindle cells and collagen bundles, with a variable amount of collagen surrounding the spindle cells. Mitoses are present in the tumor cells but nuclear atypia is not seen

Acknowledgements

Disclosure: The authors declare no conflict of interest.