尾椎疼痛的疼痛部位在尾骨區域，並且有幾種疾病可以有相似的尾骨疼痛並具有類 似的臨床表現，是需要做鑑別診斷。在這裡，我們介紹一例有尾椎疼痛個案，她有尾骨 創傷史而且其疼痛症狀與尾椎疼痛相同。最初的x射線膠片沒有在骶尾關節或尾骨上顯示 任何異常圖像。在超音波影像撿查時，我們發現鄰近尾骨的軟組織有異質低迴聲積液。 組織抽吸結果顯示肛門周遭膿瘍。臨床診斷上需要隨時留意任何可能的感染，另一點即 是超音波撿查對於疾病診斷確實實用性高，可以更進一步的評估患者並鑑別診斷疾病。

Coccydynia is pain in the region of the coccyx. There are several diseases that may have clinical presentation similar to coccydynia. Here, we present a case who had tailbone trauma history and clinical presentation similar to coccydynia. The initial x-ray film showed there was not any abnormal finding on sacrococcygeal joint or coccyx. Under ultrasound examination, we found subcutaneous edematous soft tissue with heterogeneous hypoechoic effusion collection near to coccyx. Tissue aspiration was performed later and perianal abscess was proven. Hence, we must keep alert to possible infectious diseases in clinical practice, and ultrasound examination can be a useful tool for differential diagnosis.