It has been claimed that the distinction between a simple cyst and a simple noncomplicated hydatid cyst cannot be made by ultrasound examination. It is very important to make this distinction before attempting a diagnostic or therapeutic puncture of a cyst, at least in geographic areas where echino· coccosis is endemic. The authors report an ultrasound sign that makes this differential diagnosis possible. (Key words: hydatid cyst; echinococcosis;. simple cyst differential diagnosis; hydatid sand)Because of the dangers of rupture, anaphylactic shock, and peritoneal hydatid seeding, puncture of cystic lesions for diagnostic or therapeutic purposes is contraindicated in areas where hydatidosis is endemic.Although the ultrasound findings in human hydatidosis have been describedt J-4 no way to differentiate between a simple cyst and a simple hydatid cyst has been reported. On the contrary, both Niron and Ozer and Itzchak et al:' pointed out that "it is impossible to make this differential diagnosis by ultrasound examination."About a year ago, casually, we observed bright falling echoes within a large, simple, noncomplicated hydatid cyst. These echoes were seen during real-time observation after a sudden change in position of the patient. Two or three seconds later, the echoes had disappeared. We shook the patient, and again we could see small dense mobile echoes, that "flew" and fell rather fast. In sedimentation rate and appearance, the echoes were similar to snowflakes falling on a quiet night; 2-3 seconds later, no echoes could be found. We repeated the experiment with B-mode echography and obtained the same results. Since then, we have "shaken" other patients with hydatid cysts, with the same results.Here, we report what we think is a ultrasound sign to make possible the differential diagnosis of a simple hydatid cyst.• Hipolito lrigoyen 1441, General Roca, Rio Negro, 8332 Argentina.
RESULTSThe pattern indicative of a hydatid cyst was found in the scans of four patients, three female and one male, ranging in age from 7 to 63 years. All these diagnoses of hydatid cyst were confirmed by surgery. There were also two patients who had large. , simple, proven hydatid cysts on whose scans the sign could not be found.A hydatid cyst was removed surgically from a 7-year-old patient. It was a simple noncomplicated cyst about 7 em in diameter. We scanned the cyst in a water bath using the B-mode scanner, before and after shaking it. Internal echoes could be demonstrated only in the second scan, and in a matter of a few seconds they disappeared. We then punctured the cyst with a needle to withdraw a specimen from its top, before and after shaking it. Scolices were found in smears of the second sample only. The cyst had no daughter cysts, nor was there any debris other than a very small amount of hydatid "sand" that could hardly be seen after opening the cyst. The hydatid sand is composed of hooks, scolices, and brood capsules 5 about 100 to 500 j.Lm in diameter. The high specific gravity of the hydatid sand makes it sedimen...
