![]() Insufficiency fracture in the para-acetabulum, with features mimicking those of a malignant bone tumor. These findings may be features for the differentiation of stress fractures from malignant bone tumors. In this case, there were some MRI findings: fracture line curvilinear superior acetabulum low signal intensity on T1- and T2-weighted images significant bone marrow edema the enhancement increased only gradually the unclear border of the contrasted edge and absence of associated soft tissue masses. On contrast-enhanced MRI, malignant bone tumors are enhanced early. There are some reports that it was difficult to distinguish from malignant bone tumors by X-ray or MRI. Supra-acetabular IFs were firstly described by Cooper et al. In this case, there were no electrolyte or hormonal abnormalities, and it was suspected that the less common male primary osteoporosis was the underlying cause of the fracture. Osteoporosis affects women four times more frequently than men, and it is said that osteoporosis in males is more often secondary osteoporosis. Rheumatoid arthritis, radiation therapy, and steroid therapy are also risk factors. Most IFs occur in older women with postmenopausal osteoporosis. Supra-acetabular IFs are rare, and this case of an IF of the supra-acetabulum required differentiation from a pathological fracture due to a malignant bone tumor. In the pelvis, they are produced in the pubis, ilium, and sacrum. They commonly occur in the spine, pelvis, and lower extremities. IFs are caused by normal stresses for bone with weakened mechanical strength. Positron emission tomography showed accumulation of standardized uptake value (SUV)max3.5 in the right supra-acetabulum. A bone scintigram showed accumulation in the right supra-acetabulum. Moreover, nuclear examinations were performed to distinguish between benign or malignant and to check whether there were other bone lesions. There were no inflammatory findings in the blood results, nor were there any abnormalities in his electrolytes, thyroid hormones, or tumor markers. Blood testing was carried out for differential diagnosis considering bone metastasis from carcinoma or secondary osteoporosis. A malignant bone tumor at right supra-acetabulum was suspected by CT and MRI, and he was referred to our department. ![]() Contrast-enhanced MRI showed the lesion gradually enhanced (Fig. The lesion was not suppressed by short TI inversion recovery. Magnetic resonance imaging (MRI) with T1 weighting showed a linear low signal and an equivalent signal surrounding it at the right supra-acetabulum, and the linear low signal and high signal surrounding it were seen on the T2-weighted image. The computed tomography (CT) scan showed evidence of sclerosis with a periosteal reaction in the right supra-acetabulum (Fig. 1), so further examinations were performed. X-rays showed no obvious abnormalities (Fig. His history included appendicitis and hypertension. This is likely to be bone marrow edema associated with the stress fracture, and we believe this to be a useful finding that may help in differentiating a stress fracture from a pathological fracture secondary to a malignant lesion.Ī 74-year-old Japanese man presented to the previous hospital complaining of right hip pain. On magnetic resonance imaging, the boundary around the fracture line was unclear and a signal change that was gradually enhanced by gadolinium was observed. Initially, a pathological fracture associated with a malignant lesion was considered. This case was diagnosed as an insufficiency fracture of the supra-acetabulum in a male patient with primary osteoporosis by biopsy specimen. The bone density was 66% for the lumbar spine (young adult mean, L2–4), and blood biochemistry showed an increase in alkaline phosphatase and total type I procollagen N-terminal propeptide. A computed tomography-guided needle biopsy was performed, but no tumor cells were observed, therefore the lesion was presumed to be a fracture healing. On the contrast-enhanced magnetic resonance imaging, the lesion was still unclear and the whole area was gradually enhanced. A linear, low-signal region and its surrounding equal signal region were observed at the same site in the T1-weighted image, and a linear low-signal region and high signal region were observed in the surrounding area in the T2-weighted image. Magnetic resonance imaging showed an abnormality in the right supra-acetabulum, and he was referred to our department. Case presentationĪ 74-year-old Japanese man presented to the hospital because of right hip joint pain. We report a rare case of a stress fracture of the supra-acetabulum that required differentiation from a malignant bone tumor. The supra-acetabulum is a common site for malignant bone tumors, which can be difficult to differentiate from insufficiency fractures.
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