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Imaging modalities presently available for the clinical diagnosis and basic research of bone tumors are versatile including radiography, conventional x-ray tomography, angiography, CT scan, MR imaging, ultrasonography and nuclear bone scan. Of these, radiography and high resolution CT scan are the two most useful means to image bone morphology both in normal and pathologic conditions. However, these two modalities are unable to provide any useful metabolic or chemical information in bone diseases as nuclear bone scan does. 99mTc-phosphate bone scan has unique capability to disclose both the morphologic and metabolic profile of most bone pathologies including tumors. Bone scan is useful not only for morphologic diagnosis but also for chemical profile studies in almost whole spectrum of bone diseases including metastasis in the preradiographic stage, cryptic tumor invasion, disseminated metastasis and multiple familial exostosis. It is, however, to be mentioned that the ordinary planar bone scan obtained using a parallel hole collimator has limited image resolution due to the miniaturizing of image to 1/15 of the life size. Fortunately, this critical drawback can be remedied by pinhole scan which can readily restore image to an appropriate size, tremendously enhancing the image quality and hence the sensitivity and specificity. Thus, pinhole scan has been amply shown to be a new potential diagnostic tool in skeletal oncology. Indeed, many subtle morphologic and metabolic alterations, which are not seen on the ordinary planar or even SPECT images, are portrayed in an amazing detail by pinhole scan. Some of the typical applications of pinhole scan are the delineation of metabolic profile of various tumors and tumorous conditions, precise localization of nidus in osteoid osteoma, the detection of intramedullary skip metastasis in giant cell tumor and osteosarcoma, the differential diagnosis of osteosarcoma, giant cell tumor, simple and aneurysmal bone cyst and ossifying and non-ossifying fibromas and unexplained bone pains. Thus, it follows that more systematic and widespread use of pinhole scan is to be encouraged with the anticipation of founding a new domain of combined anatomic and metabolic diagnosis of tumors and tumorous conditions of bone. This article describes the scope and practical applications of pinholesan in skeletal oncology.
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