In a letter to the editor [1] Hesslewood recently drew attention to the fact that a patient suffered serious neurological complications following the intrathecal administration of technetium-99m diethylene triamine pentaacetic acid (99mTc-DTPA). No information on the patient, type of DTPA kit or the preparation used was given. This report, however, raises the question of whether the continued use of 99mTc-DTPA for cisternography can be supported.In our previous report referenced in the letter, two of the first 15 patients we studied developed adverse reac-tions [2]. Since this publication is not readily available, a short summary of this study and of our subsequent experience using 99mTc-DTPA for intrathecal use seems to be appropriate.The adverse reactions we reported were apparently provoked by the sequestration of calcium and magnesium ions in the cerebrospinal fluid at the site of the injection. This problem was traced to the DTPA kits of a manufacturer which contained DTPA as the sodium salt and not CaNa3DTPA. Trisodium DTPA is able to strongly complex many kinds of metallic ions such as Ca, Mg and Tc, whereas calcium trisodium DTPA can bind Tc but not Ca or Mg.In isolated ischiatic nerves of rats, nerve conduction could be irreversibly blocked using HzNa3DTPA solutions, even at relatively low concentrations (5 mEq/1), while CaNa3DTPA caused no effect, even at much higher concentrations (20 mEq/1). We also found that stan- Table 1. DTPA kits containing free acid or sodium DTPAnot suitable for intrathecal use

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Liver scintigraphy demonstrated areas of increased radiocolloid uptake in three cases with obstruction of the superior vena cava and extensive collateral circulation through the veins of the thoracic wall. The pattern of the hyperactive zones is indicative of predominant vascularization of the liver via the umbilical vein, with high colloid particle deposition in the quadrate lobe and adjacent part of the right lobe. These liver regions vascularized by the first intrahepatic branches of the umbilical vein as demonstrated by postmortem angiography, probably extract a great portion of the tracer dose, resulting in localized hyperactivity. An identical liver scan image was, however, found in a fourth case without evident superior vena cava syndrome. In this patient, presenting with a bronchus carcinoma with paratracheal metastatic lymph nodes, there is no explanation metastatic lymph nodes, there is no explanation (collateral circulation without vena cava obstruction?) for the abnormal tracer distribution within the liver.

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Two cases of mediastinal localization of parathyroid adenoma are presented, in which technetium-thallium subtraction scintigraphy yielded a positive result. Both patients had already undergone a negative surgical neck exploration. We suggest that, in case of negative subtraction scintigraphy and negative surgical exploration in proven primary hyperparathyroidism, subtraction scintigraphy should be repeated with emphasis on the superior mediastinum, and in all cases, the use of a non-zoom, large field of few procedure is recommended for technetium-thallium subtraction scintigraphy.