Triangulation method for percutaneous needle guidance: the angled approach to upper abdominal masses.

A method for percutaneous biopsy and aspiration of posteriorly located retroperitoneal, adrenal, renal, and hepatic masses using computed tomographic or sonographic guidance of an angled needle was used on 17 occasions in 16 patients. The technique uses the Pythagorean theorem for right triangles, and tangent ratios to provide an extrapleural, extraperitoneal route in the prone position for otherwise inaccessible lesions. The more precise geometric planning reduced time to complete the procedure and avoided the complication of pneumothorax which had been previously encountered. Needles were accurately positioned in all patients, and a positive diagnosis was achieved in 13 (three patients had intrahepatic hemangiomas and there was one false-negative necrotic carcinoma).