Compromised CT detection of extracranial malignant neoplasms by steroid treatment

Computed tomographic attenuation coefficients in six rabbit thigh V2 carcinomas were studied before and after steroid treatment. In four V2 tumors with effective steroid treatment, the density difference between V2 carcinoma and normal muscles decreased on both pre- and postcontrast scans (17.9 and 21.8 Hounsfield units, respectively--HU: 1,000 scale) attributable mainly to altered tumor X-ray absorption; 3 weeks after steroid withdrawal, normal and malignant tissue density differences increased and returned toward base line. Two V2 tumors failed to respond to steroids; the precontrast density difference between V2 carcinoma and normal muscle was nearly constant, and the postcontrast density difference increased by 6.8 HU. In patients taking steroids, malignant tumors may become isodense with the surrounding normal tissue and be difficult or impossible to detect. Changes in tumor density may also prove to be a useful marker off therapeutic efficacy.