Metformin and contrast media: where is the conflict?

Intravascular administration of iodinated contrast media to patients who are receiving metformin, an oral antidiabetic agent, can result in lactic acidosis. However, this rare complication occurs only if the contrast medium causes renal failure, and the patient continues to take metformin in the presence of renal failure. Because metformin is excreted primarily by the kidneys, continued intake of metformin after the onset of renal failure results in a toxic accumulation of this drug and subsequent lactic acidosis. To avoid this complication, metformin must be withheld after the administration of the contrast agent for 48 hours, during which the contrast-induced renal failure becomes clinically apparent. If renal function is normal at 48 hours, the metformin can be restarted. There is no scientific justification for withholding metformin for 48 hours before administration of the contrast medium, as currently recommended in the package insert. The authors review the pharmacology of metformin and present a departmental policy for managing patients with diabetes who receive metformin and who require intravascular administration of iodinated contrast media.

An artificial intelligence program for the radiologic diagnosis of brain lesions.

A software program has been developed that uses a frame-based expert system for differential diagnosis in neuroradiology. A frame-based expert system is used to store the magnetic resonance (MR) and computed tomographic (CT) imaging characteristics of over 100 known brain disorders in object-like entities. The frames are organized in a hierarchic structure in which lower order frames inherit attributes from higher order frames, with the highest frame containing information that applies to all the other frames. Program execution follows a consultation paradigm with a dynamic database. A decision tree menu provides a user-friendly interface with which to navigate through the network, based on features of the lesion as depicted on MR and CT images. The system can provide a differential diagnosis based on the MR imaging findings alone with information criteria including the signal intensity of the lesion on T1- and T2-weighted images, the location of the lesion, and the presence or absence of mass effect. The differential diagnosis may be further refined by adding CT-related information, including CT attenuation and the presence or absence of calcification and contrast enhancement.

Antenatal unilateral hydrocephalus.

Fetal ventriculomegaly usually involves both lateral ventricles. If dilatation of the dependent lateral ventricle is seen, it might be assumed that the condition is bilateral and symmetric and that reverberation artifact is obscuring the ventricle nearer to the transducer. However, unilateral hydrocephalus can occur, though rarely and usually as a result of unilateral obstruction of the foramen of Monro. Careful attention to visualization of the obscured hemisphere is emphasized. In the patient described here the condition was associated with frontoethmoidal encephalocele.

Prenatal demonstration of a cervical myelocystocele.

Myelocystocele is a rare spinal cord disorder and has not been described prenatally. We report a case in which prenatal ultrasound and magnetic resonance imaging (MRI) demonstrated a posterior cervical mass which was initially thought to be a meningocele or an atypical cystic hygroma. Surgery performed at 1 day of age showed this to be a myelocystocele. Therefore, the differential diagnosis of an extracranial cystic mass in the posterior cervical region should be expanded to include myelocystoceles.

Prenatal diagnosis of urinary tract malformations.

Oligohydramnios, abnormal kidneys or an abnormal bladder, separately or in combination, are the usual ultrasonographic signs that call attention to an anomaly of the fetal urinary tract. After briefly outlining the normal anatomic features, the author elaborates on these three major signs and discusses bilateral renal agenesis, paradoxic polyhydramnios, obstructive and nonobstructive hydronephrosis, renal cystic disease and urethral obstruction. Radiologists who perform obstetric ultrasonography must be familiar with the general pathophysiologic principles that pertain to the fetal urinary tract, as well as their ultrasonographic manifestations.

Spontaneous intrajugular migration of long-term central venous access catheters.

Two patients with long-term central venous access catheters introduced via the right subclavian vein demonstrated catheter migration into the right internal jugular vein several months after satisfactory catheter placement. One patient developed internal jugular vein thrombosis, which was treated with direct infusion of urokinase before catheter removal. In the other patient, the catheter was repositioned by using an intravascular snare loop, which was introduced via the femoral vein. In the first patient, an interim chest radiograph suggested the mechanism by which the catheter had migrated and provided a clue for early detection of catheter migration.

Prenatal ultrasonographic diagnosis of dicephalus conjoined twins.

The authors report the prenatal diagnosis by ultrasonography of dicephalus dipus dibrachius conjoined twins (with two heads, one body, two legs and two arms) at 31 weeks' gestation. They discuss the types of conjoined twinning and their frequency of occurrence and the criteria for prenatal diagnosis, and they offer recommendations for management.

Peptic ulcer-induced gastroaortic fistula: difficulty in making the diagnosis with selective angiography.

We report a patient who had a gastroaortic fistula. This rare, potentially curable cause of torrential upper gastrointestinal hemorrhage is usually secondary to perforation of a gastric ulcer into the distal thoracic aorta. Hiatal hernia and previous gastroesophageal surgery (as in our patient) are important contributing factors in its genesis. It is essential to suspect this condition clinically so that the correct angiographic diagnosis can be made by biplane mid-stream thoracoabdominal aortography.

An appraisal of pelvic ultrasound: a survey of gynecologists.

The clinical role and perceived usefulness of gynecologic ultrasonography (US) were determined by a survey of the 74 active members of the Eastern Ontario Obstetrical and Gynecological Society using a mailed questionnaire. There were 58 gynecologist respondents, 30 of whom had completed the specialty training before 1977 (Group I) when diagnostic US became generally available locally, and 28 whose training ended in or after 1977 (Group II). In general both groups found pelvic US to be useful and were cognizant of some of its potential benefits. Group II respondents tended to rely more upon both obstetrical and gynecological US than those in Group I, whereas Group I respondents were less familiar with some of the pitfalls or limitations of US in gynecologic practice. This suggests that the development of clinical decision-making skills by obstetric-gynecologic residents is influenced by the availability of US during their training. It may be of benefit to address the subject of relevant pitfalls in US by continuing medical education.

Anticoagulant effects of contrast materials: in vitro study of iohexol, ioxaglate, and diatrizoate.

It has been reported that clot formation may occur when blood is mixed directly with nonionic contrast medium in a syringe during angiography. To investigate this possibility, we performed three in vitro experiments to determine the anticoagulant properties of a low-osmolar, nonionic contrast medium (iohexol); a low-osmolar, ionic medium (ioxaglate); and a high-osmolar, ionic medium (diatrizoate). In the first experiment, human arterial blood was incubated at room temperature in an angiographic syringe with each of the three media for 60 min, after which the mixture was filtered for clots. In the second experiment, the clotting times of venous blood in heparinized saline or serial dilutions of the three agents were determined. In the third experiment, the partial thromboplastin time of platelet-poor plasma in heparinized saline or serial dilutions of the three agents was measured. No clots were observed in any of the arterial blood samples. Iohexol prolonged the normal 15-min clotting time of venous blood to 160 min, compared with a clotting time of at least 330 min for ioxaglate and diatrizoate. Iohexol prolonged the normal 36-sec partial thromboplastin time of platelet-poor plasma to 40 sec, compared with 50 sec for diatrizoate and 54 sec for ioxaglate. Our data show that iohexol, like ioxaglate and diatrizoate, inhibits clot formation when mixed with blood in a syringe. It prolongs the clotting time to approximately the same degree as 600 U/l of heparinized saline, but to a lesser degree than the other two media. All three media have a minimal effect on the partial thromboplastin time. Our results do not show any risk of clot formation in the usual clinical setting in which there is inadvertent mixing of blood with iohexol, ioxaglate, or diatrizoate in an angiographic syringe.

Unusual causes of sonographic nonvisualization or nonrecognition of the gallbladder: a review.

Nonvisualization of the gallbladder by ultrasound in a fasting patient usually indicates calculous gallbladder disease. However, a number of other less common conditions can prevent gallbladder visualization or recognition. The latter occurs when the location or the morphology of the gallbladder is so altered that the gallbladder is difficult to identify. These conditions can be classified as: (1) congenital anomalies, (2) gallbladder contraction not due to stones, (3) conditions that cause shadowing or reverberation from the near wall of the gallbladder, and (4) the solid gallbladder pattern. Their distinction is important to proper patient management.

The role of the coracoacromial ligament in the impingement syndrome. A clinical, radiological and histological study.

Seventeen patients with a painful arc syndrome and tenderness over the coracoacromial ligament were selected to demonstrate the changes in the coracoacromial ligament in the impingement syndrome. Plain X-ray examination was normal and a preoperative subacromial bursogram demonstrated impingement in only three out of 17 patients. However, at operation the subacromial space under the coracoacromial ligament, which normally admits the tip of the little finger, appeared unusually tight and barely accessible in 15 out of 17 patients. Histological examination of the biopsied ligament showed degenerative changes but no increase in fibrous tissue. We conclude that in the absence of bony overgrowth the initial change is an increased volume of the soft tissues in the subacromial space. Consequently, the space is compromised by the swelling of its contents, which exert abnormal pressure on the overlying coracoacromial ligament and cause degenerative changes in the ligament. The symptoms of impingement appear because of the unyielding nature of the coracoacromial ligament. Subacromial bursography may not be a reliable test when the coracoacromial ligament is the site of impingement.