br Case report Radiographs showed a lytic lesion in the
Case report Radiographs showed a lytic lesion in the left ilium adjacent to the sacroiliac joint (Fig. 1). Computed tomography (CT) (Fig. 2) showed a 5.5×5.0×3.4cm3 lytic lesion in the left ilium; the sacrum was not involved. The lesion was of uniform density with no bone or cartilage matrix formation. The cortex was discontinuous and the boundary well-defined. CT values were 39HU before enhancement and 57HU after enhancement. A chest CT revealed no lung lesions. Magnetic resonance imaging showed medium and high signals in T1- and T2-weighted images, respectively, with uneven enhancement. The maximum standardized uptake value on positron emission tomography was 2.9 and no other lesions were detected. Serum alkaline phosphatase, calcium and phosphate concentrations were normal. Pathological examination of the operative specimen showed that a wide resection margin had been achieved (Fig. 3). We again observed a funicular structure of vacuolated tumor cells in a background of mucus. The cells had a mildly atypical appearance. Immunohistochemical staining showed the following: cytokeratin (CK) (+++), CK7 (focal +), CK8 (+++), CK18 (focal +), CK19 (+++), epithelial membrane antigen (focal weak +), S-100 (scattered cells +), D2-40 (−), brachyury (+), and vimentin (+). Therefore, the microstructure, morphology and immunohistochemistry results were consistent with a classical chordoma diagnosis (Fig. 4).
Discussion The most common site of chordomas is the sacrum, but they can also occur in the mCAP of the cranium and the mobile spine [5,6]. Most patients with chordomas are in their fifth to seventh decades. The ratio of male to female patients is about 2–3:1. Because affected patients often present with a long history of sacral or flank pain, diagnosis and treatment are often delayed. When these tumors enlarge, they can invade pelvic organs or nerve roots, causing organ and lower limb dysfunction. It is extremely rare for chordomas to occur in sites other than the sacrum, base of the cranium, and mobile spine. We have not found any previous reports of iliac chordomas. In theory, chordomas can only occur in sites that were occupied by the embryonic notochord. These sites include the whole length of the spine from the skull base to the sacrum, most commonly at one end or the other. Imaging studies of this rare tumor showed the iliac lesion was adjacent to the sacrum; however, it appeared to have originated from the ilium without any involvement of the sacrum. An biopsy revealed chordoma, which was completely unexpected. The pathologists therefore carefully reviewed the pathology of the operative specimen and again concluded the diagnosis was chordoma. This rare case changed our understanding of both chordomas and primary iliac tumors. We could find only case reports of a chordoma occurring in non-axial bone . The most common primary malignant tumor of the ilium is chondrosarcoma; osteosarcoma, Ewing sarcoma, and malignant fibrous histiocytoma are also common, whereas other primary malignant bone tumors are rare . Common benign tumors of the ilium include giant cell tumors, osteochondromas, simple bone cysts, and fibrous dysplasia; chondroblastomas, Langerhans cell disorders, and bone hemangiomas can also occur . Our patient was a 45-year-old man, which is consistent with the reported age range and sex for subjects with chordomas. These lesions should be differentiated from other benign and malignant tumors. Chondrosarcomas are the most frequent primary malignant bone tumor of the ilium, usually occurring in persons aged more than 40 years . Imaging usually shows osteolytic destruction with well-demarcated boundaries, as was true in our case. However, a calcified matrix and obvious soft tissue mass are characteristically found in subjects with chondrosarcomas. Osteosarcomas occur mainly in adolescents, but have been reported in older patients with pelvic lesions . These high grade tumors usually cause severe local symptoms and have aggressive characteristics. About 5% of giant cell tumors occur in the pelvis , and affected patients are characteristically younger than our case. Imaging shows osteolytic destruction with no bone or cartilage matrix formation. These lesions usually have obvious cortical expansive growth with soap bubble-like changes. A liquid plane can be found on MRI examination. Thus, the findings in our case are inconsistent with any other common malignant tumor.