[A case of calvarial aneurysmal bone cyst: transcranial contrast sonographic examination with pulse inversion harmonic imaging method].

A 31-year-old female came to our hospital complaining of left frontal bulging with pain on 10 August 2000. The head x-p showed a radiolucent lesion and bulging at the same calvarial site. CT scan and MRI showed fluid-fluid levels, diploic cyst, deformity and hypertrophic calvarial change. There was a partial hypervascular part of cyst adjacent to the left frontal base by selective left external carotid angiography. Harmonic image is a contrast specific imaging modality that uses the nonlinear properties of contrast agents by transmitting at the fundamental frequency and receiving at multiples of these frequencies. Pulse inversion harmonic image(PIHI) using pulse inversion to eliminate and strengthen the harmonic frequency is more effective than conventional harmonic imaging. Transcranial sonographic examination showed hyper- and hypoechoic appearances in the cyst around abnormal hyperechoic appearances of the calvarial site. The transcranial contrast sonographic images with PIHI (hereinafter TCIpi) demonstrated an enhanced intracystic lower stratum and nearby the diploic part. That modality facilitates better visualization than the harmonic imaging method, enabling differentiation of vascular from avascular areas. As contrast agents are microbubbles, those are restricted in the vascular canal space. So TCIpi findings proved to be a blood circulation of the tumor, cyst and neighboring tissue. Enhanced areas changed by every minute and disappeared gradually. The findings were probably based on the vascular component of the tumor. We obtained images similar to those with CT and MRI. The patient underwent on 21 August. The tumor was removed along with the surrounding skull component. Fresh and old blood were mixed in the cyst. The clinical and pathological diagnosis was aneurysmal bone cyst. The postoperative course was uneventful and she was discharged on 29 August. Aneurysmal bone cyst is a rare calvarial tumor. An diagnostic finding is fluid-fluid levels that appear in approximately 30% of aneurysmal bone cysts. However, this is not a specific finding and has also been reported to occur in osteosarcoma, malignant fibrous histiocytoma, fibrous dysplasia, synovial sarcoma, hemangioma and simple bone cyst. Therefore, diagnosis of aneurysmal bone cyst is based on a combination of the various imaging applications, clinical and pathological findings. Gometz reported that sonographic examination was superior to any diagnostic imaging studies for aneurysmal bone cyst. Furthermore, the perfusion examination like TCIpi can directly observe blood circulation channels in tissue, so the specific enhancement changes of aneurysmal bone cyst could be observed. TCIpi is a useful method for diagnosis of aneurysmal bone cyst.