Background： To investigate magnetic resonance imaging (MRI) manifestation of transarticular invasion of primary bone tumors and tumor-like lesions near the sacroiliac joint and to compare the transarticular invasion incidences and types of primary bone tumors and tumor-like lesions in different locations, of different pathological types, or of different pathological grades.
Methods: A retrospective analysis of 128 patients . The diagnosis of the patients was confirmed by surgical findings and pathological examination. The primary tumor was in the ilium(87 patients) and sacrum(41 patients). Eighty men and 48 women with an average age of 32.5 years . Based on pathology grading systems, the tumors were divided into a high-grade malignant group (Group 1), low-grade malignant group (Group 2) and benign tumors/neoplasia group (Group 3). Transarticular invasion included 3 types: invasion across the ligament portion (Type 1), across articular cartilage (Type 2) and across periarticular tissue (Type 3).
Results: Transarticular invasion of primary bone tumors and tumor-like lesions near the sacroiliac joint were diagnosed in 33 patients (25.8%). Transarticular invasion incidences were not significantly different between primary iliac and sacral tumors ,group 2 and group 3( P > 0.05). However, the transarticular invasion incidences were significantly different between group 2 or 3 and group 1 (P < 0.01). 33 patients with transarticular invasion, the invasion types included 31 type 1, 15 type 2 and 5 type 3 invasions. A significant difference was observed between different invasion types (P < 0.01).
Conclusions: MRI is a highly sensitive method to diagnose transarticular invasion of primary bone tumors and tumor-like lesions near the sacroiliac joint. The transarticular invasion incidence is not significantly different between primary iliac and sacral lesions. Tumor invasion across the sacroiliac joint can be present in both primary bone tumors and tumor-like lesions but predominantly with high-grade malignant conventional osteosarcoma or Ewing's sarcoma. Transarticular invasion across the articular ligament portion is more common. No significant difference is evident between the 3 types of invasion in the groups with different pathological grades, suggesting that the transarticular invasion types are not related to benignity or malignancy or to the malignant degree of a tumor.