Subchondral cysts (or geodes) are common in osteoarthritis (OA), usually in association with other typical signs, i.e., joint space narrowing, subchondral bone sclerosis, and osteophytosis. However, large lesions without the typical signs of OA or lesions located outside the weight-bearing areas are unusual and may be confused for other conditions, in particular, those of tumoral origin. We report the findings in a 48-year-old man who had been complaining of left buttock pain for 3 years, getting worse over the last year, and an evolutive limited range of motion of the hip. The pain was increased by weight-bearing and was not relieved by nonsteroidal anti-inflammatory drugs. Radiographs and CT showed a large multilocular lytic lesion within the femoral head and a large lytic lesion in the left ilio-ischiatic ramus, raising the question of bifocal tumoral involvement. On MRI, the lesions had low signal intensity on T1- and high signal intensity on T2-weighted MR images, with subtle peripheral enhancement on post-contrast T1-weighted images. CT arthrography, by demonstrating a communication between the femoral head and ischiatic cysts and the joint space allowed us to definitively rule out malignant conditions and to make the diagnosis of subchondral bone cysts. Total hip arthroplasty was performed. Pathological analysis of the resected femoral head and of material obtained at curettage of the ischiatic lesion confirmed the diagnosis of degenerative geodes. This case illustrates an atypical bifocal location of giant subchondral cysts in the hip joint mimicking lytic tumors, in the absence of osteoarthritis or rheumatoid arthritis, and highlights the role of CT arthrography in identifying this condition.

中文翻译：

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髋关节双焦点巨大软骨下囊肿的罕见观察：CT关节造影和MRI的诊断作用，与病理相关。

骨关节炎（OA）中常见软骨下囊肿（或结点），通常伴有其他典型体征，例如关节间隙狭窄，软骨下骨硬化和骨赘。但是，没有典型骨关节炎征象的大病变或位于负重区域之外的病变是不寻常的，可能会与其他疾病（尤其是肿瘤起源的疾病）相混淆。我们报告了一名48岁男子的发现，该男子抱怨左臀部疼痛已有3年，在过去的一年中情况更加恶化，并且髋关节活动范围有限。负重会增加疼痛，而非甾体类抗炎药并不能缓解疼痛。影像学检查和CT扫描显示股骨头内有较大的多眼溶解性病变，而左侧虹膜坐骨支有较大的溶解性病变，提出了双灶性肿瘤受累的问题。在MRI上，病变在T1上的信号强度较低，而在T2加权的MR图像上的信号强度较高，而造影剂T1加权后的图像则具有微弱的周围增强。CT关节造影通过证明股骨头与坐骨囊肿和关节间隙之间的连通性，使我们能够明确排除恶性疾病并诊断软骨下骨囊肿。进行全髋关节置换术。对切​​除的股骨头和在刮除缺血性病变处获得的材料进行病理学分析证实了变性大肠癌的诊断。这个案例说明了在没有骨关节炎或类风湿关节炎的情况下，模仿溶解性肿瘤的髋关节中巨大的软骨下囊肿的非典型双灶位置，