Synovial chondromatosis of the hip with atypical MRI morphology and mistakable clinical symptoms — a case report

A 32-year-old male presented to us with 6-month symptoms of unilateral spinal claudication (L3 right) together with lumbar pain and intermittent tenderness of the right sacroiliac joint with insidious onset and slow progression. The pain was also occasionally localized to the anterior groin or the lateral aspect of the right hip including sporadic indolent popping. Pain relief was exclusively achieved on spine flexion or positioning of the hip in a flexed and externally rotated position. The patient reported episodes of exacerbation, which could be followed by completely asymptomatic periods in which he was capable of participating in all activities, and bicycling in particular. Later, there was diffuse right thigh discomfort at night. Physical examination revealed a slight, uncomfortable limitation of range of motion of the right hip. A lumbar MRI was performed in order to exclude a spinal stenosis or nerve root compression. This was normal. Radiographs of the hip showed regular neck-shaft and center-edge angles, and a mild Pinzer-type of femoroacetabular impingement without major degenerative changes. No bone erosion, joint space alterations , or radiopaque bodies were apparent. A subsequent MRI of the hips showed the right joint space filled with a homogenous tissue that appeared slightly hyper-intense in pre-contrast T1-weighted TSE images compared to muscle (Figure 1). The mass was hyperintense and slightly inhomogenous in fat-suppressed T2-weighted TSE images (STIR). It appeared to originate from the inferior joint capsule expanding into the joint space. No signal loss corresponding to calcified areas, joint effusion, or a ruptured ligamentum capi-tis femoris could be found. The acetabular fossa was slightly eroded. In the gadolinium-enhanced T1-weighted TSE images with fat suppression (Figure 2), the tissue and the thickened synovia showed slight enhancement with a stronger enhancing rim surrounding the mass. There was no enhancement or edema of the joint surrounding soft tissue or bone. An un-enhanced thin-slice CT scan with coronal reformats revealed a slightly widened joint space of the right femoroac-etabular joint that was filled with a homogenous soft tissue-isodense material instead of fat and synovial fluid, as seen on the contralateral side (Figure 3). No calcifications could be found within the soft tissue. Slight erosion of the acetabular fossa was evident. Since all diagnostic modalities were inconclusive, an open biopsy using a minimally invasive anterolateral approach to the hip was done and revealed numerous intra-articular carti-laginous bodies. Histology verified the diagnosis of a synovial chondromatosis without any signs of malignancy. …