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U ltrasunography has become the standard approach for investigating suspected urinary tract obstruction because of its safety and high sensitivity.lJ However, it is important to understand that ultrasonography does not detect obstruction directly, but rather its usual consequence: dilatation of the renal collecting system. Unforhmately, urinary tract obstruction is not always accompanied by detectable dilatation36 In these unusual cases of nondilated obstructive uropathy, the results of conventional ultrasonography will be falsely negative, thereby misleading the physician and possibly delaying diagnosis and therapy. Most previously reported cases have been the result of retroperitoneal or pelvic malignancy or fibrosis, or have followed pelvic surgery.56 Here we report a case of nondilated obstructive uropathy caused by a ureter-al calculus in order to alert physicians to the possibility that on occasion, even obstruction due to a urinary stone may be missed by ultrasonography. While this presentation has been noted previously by radiologists,5~7-~ it has not been emphasized in the general medical literature.

Two patients are described who presented with complete urinary obstruction secondary to nonopaque uric acid stones. They were treated with percutaneous nephrostomy for urinary diversion and urinary alkalinization by local irrigation and oral sodium bicarbonate therapy with complete dissolution of the stone after 16 and 21 days of therapy. Percutaneous nephrostomy with urinary alkalinization is a reasonable, relatively safe alternative to surgical stone removal for patients with obstructing uric acid stones.

A double-blind clinical trial was performed in 60 patients to compare Hexabrix (ioxaglate meglumine and ioxaglate sodium) and Renografin-60 (diatrizoate meglumine and diatrizoate sodium). Use of Hexabrix produced higher urinary iodine concentrations, lower urine volumes at 30 minutes, and excretory urograms significantly better in diagnostic quality, as rated by four independent observers. There was no difference in nephrogram quality between contrast agents. Patients receiving Hexabrix had less of an increase in heart rate and demonstrated a slight rise in mean arterial blood pressure, rather than the biphasic rise then fall seen with Renografin-60. There was no significant change for up to 96 hours after urography in results of hematology, clinical chemistry, or urinalysis, except for an increase of 0.005 in urine specific gravity with Renografin-60. Patients reported significantly less body heat, heat in the injection arm, and overall discomfort with Hexabrix. There was a similar amount of nausea and vomiting in the two groups. Hexabrix also caused histaminic-type reactions in three patients.

In equivalent doses for intravenous urograms conventional ionic contrast agents give iodine concentrations in the urine of approximately 30 mg iodine/ml, nonionic contrast media provide approximately 50 mg iodine/ml, and the ionic dimer Hexabrix approximately 70 mg iodine/mL. These new low osmolality, contrast media provide significantly higher urinary iodine concentrations than conventional ionic contrast media, provide better diagnostic quality excretory urograms, better patient tolerance, and fewer adverse side-effects and serious reactions. These new low osmolality, contrast media have significant advantages in intravenous urography in both safety and efficacy when compared to conventional higher osmolality contrast media.

The effect of .3 cc of 1:1000 epinephrine on iodine concentration, total iodine content, fluid volume and radiographic quality was evaluated in knee arthrograms in dogs. With the addition of epinephrine the iodine concentration and total iodine content were significantly higher initially and remained significantly higher than in controls over a one hour period. The fluid volume in the knee was significantly lower with epinephrine. Initially both contrast absorption and dilution have major effects in decreasing iodine concentration. With increasing time the effect of contrast absorption becomes the major factor, having a two of three times greater effect on decreasing iodine concentration. With epinephrine radiographs were judged significantly better early and while the quality deteriorated rapidly in the controls the enhanced quality with epinephrine persisted up to one hour. Epinephrine is a very useful adjunct in enhancing the quality of knee arthrography.

A spectrum of rare urachal abnormalities in the adult is described, including urachal cyst, infected urachal cyst and abscess, and urachal carcinoma. The clinical and radiographic features are presented, and diagnosis using ultrasound, computed tomography, and needle aspiration is discussed. Treatment of infected urachal cysts with percutaneous catheter drainage is described.

The pharmacokinetics and urinary excretion characteristics of sodium diatrizoate, the new low-osmolality contrast medium iopamidol, a nonionic monomer, and ioxaglate, a monoacidic dimer, were compared. Using rabbits, experimental urography was performed at a dose of 450 mg I/kg. The lowosmolality co

Urografin 60, iopamidol and Hexabrix were studied in patients undergoing body CT scans to examine the pharmacodynamics of these contrast agents. Immediately following rapid injection, the lower osmolality media, Hexabrix and iopamidol, gave greater aortic concentration of iodine in addition to higher concentrations in the liver and spleen. These two agents also provided significantly better renal enhancement than Urografin 60, with Hexabrix giving higher levels than iopamidol. The higher early vascular concentrations of Hexabrix and iopamidol and the relative absence of side effects due to hyperosmolality and decreased toxicity may have advantages in dynamic CT scanning.

Computed tomography can aid in the distinction of calculi from both tumors and clots in the urinary tract. Its availability, simplicity of interpretation, and noninvasiveness establish it as an important diagnostic modality in selected cases when calculus is in the differential diagnosis of upper urinary tract filling defects.

The commonly accepted criteria for colon malignancy were investigated in malignant and benign polyps smaller than 3 cm in diameter. It was found that most small tumors, both benign and malignant, were sessile and smooth in outline. It was only when the polyps increased in size that their outlines became lobulated or irregular. A stalk was not seen in polyps smaller than 1 cm in diameter. Retraction at the base of a cancer was likewise not seen in these small lesions. The typical malignant characteristics became apparent only when the polyp had grown to 2 to 3 cm in diameter.

Ninety-seven patients who were undergoing excretory urography for suspected genitourinary tract abnormalities were continuously monitored for systemic blood pressure and pulse rates before (control) and after rapid intravenous injections of contrast material (1.5 ml/kg meglumine iothalamate, 60%) using a Bard pressure monitor. We report the systemic responses observed. Clinically obvious reactions to contrast medium were recorded and compared with the blood pressure and pulse rate responses. The most common response to rapid infusion of contrast medium was a transient hypotension. An increase in systemic pressure had a high association with nausea and vomiting. Significant hypotension (mean blood pressure less than 60 mm Hg) was observed in six patients (6%), but no overt clinical manifestations were present.

Twenty-three cases of polycystic disease were reviewed. All were easily detected by computed tomography. All manifested diffuse, bilateral renal cystic disease, and 74% had demonstrable hepatic cystic disease. Computed tomography is more accurate than other conventional modalities in diagnosing renal cysts, and its simplicity of operation and ease of interpretation are unmatched.

Excretory urography of a patient with an early stage of medullary cystic disease demonstrated an inhomogeneous, streaky nephrogram confined to the medulla, presumably due to accumulation of contrast material in dilated tubules. This was seen best one to two hours after contrast injection and may represent a specific urographic finding which does not appear to have been described previously in this condition.

To the Editor.— The article by Eason et al (240:670, 1978) describes the usefulness of alkalinization of the urine in the dissolution of uric acid stones. The efficacy of this treatment is now well documented. The difficulty is, as noted by Eason and colleagues, when the patient has obstruction of the collecting system. Retrograde catheterization has been used in such patients, and those references were quoted by the authors. An alternative approach is available for the obstructed patient with uric acid lithiasis. This involves the use of percutaneous nephrostomy for urinary diversion associated with the conservative medical treatment already well described. We have published an article describing this technique and the results in two patients, 1 which appeared after the article by Eason and co-authors. The use of percutaneous nephrostomy has increased as its safety and efficacy have been proved. 2 A two-catheter technique can also be used with percutaneous

• In deciding to use a new intravascular contrast medium, the considerations should be patient safety, imaging efficacy, and cost. Balancing these factors, use can be estimated. With the new low-osmolality contrast media, particularly the nonionic media, the expected increased patient safety must be balanced against the much higher cost. ( Arch Intern Med 1986;146:1717-1721)