Desmoid Type Fibromatosis in the Facet Joint of Lumbar Spine: Case Report and Review of Literature
A 31-year-old man was presented with back pain and mild numbness from the left buttock to the ankle, which developed after the previous motor vehicle accident, 1 year and 5 months ago. Physical examination did not reveal any abnormality in motor or neurological examination. The symptoms were partially improved with epidural and left L5 nerve root block.\nConventional radiographs of the lumbar spine demonstrated a bony erosive lesion with a sclerotic rim at the left L3-4 facet joint (). CT revealed an isodense soft tissue mass to the muscle at the posterior portion of the left L3-4 facet joint, which eroded both L3 inferior and L4 superior articular processes, but the articular surfaces of the both eroded facets were well preserved (). MR images demonstrated about 1.6 × 1.0 × 1.0 cm sized soft tissue tumor on the facet joint, which infiltrated beyond the posterior joint capsule. The tumor was isointense to the muscle on T1-weighted image (repetition time [TR]/echo time [TE] 700/10.8 msec) (), and intermediate to low signal intensity of the tumor between the muscle and cerebrospinal fluid (CSF) on T2-weighted image (TR/TE 4000/97 msec) (). The lesion was well enhanced by the gadolinium without evidence of the internal necrosis (). Tc99m-MDP bone scan did not demonstrate an abnormal radiotracer uptake.\nThe patient underwent bone biopsy, and pathologically, the tumor was diagnosed as a desmoid tumor. After 2 months, the tumor was completely removed with partial facetectomy.\nMicroscopically, the tumor was composed of cellular proliferation of the elongated, slender, spindle-shaped cells arranged in interlacing bundles of fibroblasts with abundant collagenous stroma (). The cellularity varied from area to area with scanty mitotic activity, and the cells infiltrated into the adjacent bone. Further, the tumor cells were found in the facet joint capsule with extracapsular infiltration. Immunohistochemical stain showed positive reactions to the smooth muscle actin (), focal positive reactions to S100 protein, and negative reaction to CD34, vimentin and desmin. The tumor was diagnosed as the desmoid tumor.\nAfter surgical treatment, the patient was relieved from pain in the lower back and buttock.