Michael Stiskal

Vascular complications in lumbar disk surgery: report of four cases

Vascular injuries in lumbar disk surgery, although rare, are serious complications which may be overlooked due to a broad range of clinical manifestations. It is important that surgeons and radiologists be aware of these potentially fatal complications and develop an appropriate symptom-based diagnostic paradigm. We reviewed 8099 consecutive cases of lumbar disk surgery, performed over a 14-year period at a single institution, for postoperative vascular complications. We identified four patients (0.05%) with lumbar disk surgery-related vascular complications: intraoperative lacerations of the abdominal aorta and median sacral artery, an arteriovenous fistula between the left common iliac artery and vein detected 19 days postdiskectomy, and a partially thrombosed aortic aneurysm with an arteriovenous fistula between the aneurysm and the inferior vena cava, diagnosed 11 months after surgery. The majority of cases in the literature of vascular injury in lumbar disk surgery were reported prior to 1965. Diagnostic approaches described in that period do not reflect the great range of diagnostic techniques available today. Angiography remains the gold standard for diagnosis and guidance as to surgical repair. However, a high index of suspicion based on clinical signs and/or the use of sonography or CT is important in the detection of these complications.

Angiographic properties of Gd-DTPA-24-cascade-polymer — a new macromolecular MR contrast agent

PURPOSE A new macromolecular MR contrast agent, Gd-DTPA-24-cascade-polymer, was assessed for MR angiography of peritumoral vessels in rats. MATERIAL AND METHODS High resolution 3D-SPGR (TR/TE 100/5ms, alpha = 90 degrees) angiograms were acquired in 10 Fischer rats bearing subcutaneous R3230 mammary adenocarcinomas. MRI was performed before, immediately and 40 min after administration of Gd-DTPA (0.1 mmol Gd/kg), and after either Gd-DTPA-cascade-polymer or albumin-(Gd-DTPA)30 (each 0.05 mmol Gd/kg). A semi-quantitative analysis of small peritumoral vessels and tumor rim enhancement was performed on maximum intensity projection (MIP) angiograms using a 4-point scoring system. A quantitative analysis compared vascular signal-to-background-(S/B), signal-to-noise-, and contrast-to-noise-ratio. RESULTS Gd-DTPA produced a transient and low-scoring vessel definition (0.2 +/- 0.1), but strong rim enhancement (score 1.7 +/- 0.1). The cascade polymer resulted in better but submaximal vessel delineation (score 1.6 +/- 0.3, S/B 5.0 +/- 0.2) and strong rim enhancement (score 1.8 +/- 0.1). Albumin-(Gd-DTPA)30 produced the best and most time-persistent angiograms (score 2.6 +/- 0.2, S/B 7.4 +/- 0.2), but minimal rim enhancement (score 0.3 +/- 0.2). CONCLUSIONS The Gd-DTPA-24-cascade-polymer demonstrated the useful combination of strong tumor rim enhancement and detailed angiographic definition of peritumoral vessels. These are advantages associated with extracellular and blood pool contrast media, respectively.

Tumor angiography using high-resolution, three-dimensional magnetic resonance imaging: Comparison of gadopentetate dimeglumine and a macromolecular blood-pool contrast agent

RATIONALE AND OBJECTIVES We compared the peritumoral vascular definition in rats using either a paramagnetic extracellular or a macromolecular contrast medium in combination with high-resolution magnetic resonance (MR) imaging. METHODS High-resolution, three-dimensional spoiled gradient-refocused acquisition in a steady state (SPGR) images were acquired from tumor-bearing Fischer-344 rats before, immediately after, and again 40 min after administration of gadopentetate dimeglumine (0.1 mmol Gd/kg; n = 10) and albumin-(Gd-DTPA)30 (0.05 mmol Gd/kg; n = 5). Small peritumoral vessels were analyzed semiquantitatively on maximum intensity projection angiograms using a 4-point scoring system; quantitative analyses included signal-to-background ratios (SBRs) and signal-to-noise ratios. RESULTS Gadopentetate dimeglumine caused a transient and low-scoring (0.2 +/- 0.1, SBR = 1.9 +/- 0.2) vessel definition but strong rim enhancement (score = 1.4 +/- 0.2). Albumin-(Gd-DTPA)30 produced persistent, high-quality angiograms (score = 2.6 +/- 0.2, SBR = 7.4 +/- 0.2) but minimal rim enhancement (score = 0.3 +/- 0.2). CONCLUSION Albumin-(Gd-DTPA)30 combined with high-resolution MR imaging produces time-persistent, detailed angiographic definition of peritumoral vessels. Vascular maps obtained with gadopentetate dimeglumine enhancement are not time persistent or of equal quality.

Magnetic resonance imaging of Achilles tendon in patients with rheumatoid arthritis.

RATIONALE AND OBJECTIVES The authors characterize the appearance of the Achilles tendon in patients with rheumatoid arthritis and differentiate this appearance from degenerative tendinopathy in patients with chronic pain of the heel using magnetic resonance (MR) imaging. METHODS Thirty patients with rheumatoid arthritis and 28 patients with chronic pain of the heel underwent MR imaging of the ankle and foot. Three radiologists independently assessed the MR images with respect to size, shape, and intratendinal signal characteristics of the Achilles tendon. The Achilles tendon was considered abnormal on MR imaging when intratendinous signal alterations or an anteroposterior measurement greater than 8 mm was seen. Physical examination of the Achilles tendons was accomplished in both groups. Operation confirmed the diagnosis of 13 patients in the second group with chronic pain of the heel. RESULTS The Achilles tendon of 83% of patients with rheumatoid arthritis demonstrated various intratendinous patterns (longitudinal, reticular, nodular) of intermediate signal intensity on all pulse sequences on MR imaging. Ninety percent of patients with rheumatoid tendinopathy showed no enlargement of the anteroposterior diameter of the Achilles tendon. In addition, all patients with rheumatoid arthritis had findings compatible with an inflammation of the retrocalcaneal bursa on MR imaging, whereas none of the patients with tendinopathy associated with chronic heel pain had retrocalcaneal bursitis. All patients, however, had enlargement of the anteroposterior diameter of the Achilles tendon. Seventy-nine percent showed various intratendinous lesions of intermediate signal intensity on all pulse sequences. Twenty-one percent of patients had an enlargement of the Achilles tendon without intratendinous changes. CONCLUSIONS Rheumatoid tendinopathy can be distinguished from degenerative tendinopathy in patients with chronic pain of the heel with MR imaging. Inflammation of the retrocalcaneal bursa and the absence of enlargement of the tendon combined with the presence of intratendinous signal alterations are characteristic findings of rheumatoid tendinopathy.

Ultrafast Computed Tomography and Three-Dimensional Image Processing of CT Sialography in Patients with Parotid Masses Poorly Defined by Magnetic Resonance Imaging

The purpose of this study was to determine the efficacy of ultrafast computed tomography (UF CT) in patients with parotid masses poorly defined by magnetic resonance imaging (MRI) and to evaluate the diagnostic potential of three-dimensional (3-D) UF CT sialography when compared with conventional CT sialograms. Thirteen patients with clinical suspicion of a parotid mass, in whom MRI was degraded by motion, underwent UF CT of the parotid region. Two radiologists independently assessed the CT and MR with respect to tumor localization, intraglandular tumor location, tumor margin characteristics, and infiltration of surrounding tissue. In 9 patients, CT sialography was performed using 3-D image processing. Anatomical details and pathologic findings were assessed by three readers using a numerical grad and compared with the findings derived from conventional CT sialography. Histopathologic specimens were obtained in all cases and correlated with the radiographic findings in a consensus manner following the blinded interpretations. UF CT and (suboptimal) MRI provided the same diagnostic information for the evaluation of tumor localization, and intraglandular location. UF CT was superior to MRI in the detection of tumor infiltration, and definition of tumor margins in 2 cases (15%), resulting in a substantial difference in treatment. Three-dimensional CT sialography offered significant improvement in demonstration of anatomic detail (2.5 +/- 0.2 vs 1.5 +/- 0.1, respectively) and pathologic findings (2.6 +/- 0.1 vs 1.3 +/- 0.2, respectively) when compared with conventional CT sialography. UF CT is a viable alternative in uncooperative patients with parotid masses. UF CT 3-D sialography has the potential to allow more precise pre-surgical planning and contributes to the diagnosis and therapy planning of parotid masses.

EFFECTS OF IOPROMIDE ON VASOACTIVE PEPTIDES AND ALLERGY-MEDIATED SUBSTANCES IN HEALTHY VOLUNTEERS

RATIONALE AND OBJECTIVES.Little information is available about the direct action of angiographic contrast media on vasoactive peptides and allergy-mediated substances in humans. This study defined the acute effects of iopromide, a nonionic contrast medium (370 mg/mL iodine), on vasoactive peptides, allergy-mediated substances, and hemodynnmic parameters in healthy volunteers. METHODS.Pulmonary digital subtraction angiography was performed in seven healthy volunteers with no cardiovascular or pulmonary disease. Iopromide was administered as a total volume of 100 mL through a 7-Fr catheter inserted in the right femoral vein. The injected volumes and duration of injection (15–20 mL/second) were kept constant. The following hemodynamic parameters were monitored continuously: results of electrocardiogram, heart rate, and phasic and mean pulmonary arterial and peripheral arterial pressures. Blood samples were obtained before and 3 to 5 minutes after injection of contrast media to determine the concentrations of the following vasoactive peptides: renin, angiotensin I-converting enzyme, angiotensin II, aldosterone, atrial natriuretic peptide, antidiuretic hormone, cyclic guanosine monophosphate, and myoglobin; and to allergy-mediated substances such as tryptase, cosinophil protein X, and eosinophil cationic protein, using radioimmunoassay techniques. RESULTS.Iopromide substantially increased atrial natriuretic peptide (48.8 ± 8.9 to 85.8 ± 13.0) and antidiuretic hormone (3.4 ± 0.3 to 4.6 ± 0.5) levels, whereas renin decreased (0.9 ± 0.1 to 0.8 ± 0.2) slightly but not significantly. Iopromide did not induce substantial changes in the other vasoactive peptides or in allergy-mediated substances after the contrast medium was injected. Similarly, cardiovascular parameters (heart rate, pulmonary and systemic blood pressures, and results of electrocardiogram) also remained unchanged after contrast injection. CONCLUSION.Iopromide caused no appreciable hemodynamic alterations associated with the changes in atrial natriuretic peptide and antidiuretic hormone and no evidence of allergy- mediated reactions in all volunteers.

Pulmonary hypertension. Response of vasoactive peptides to a nonionic contrast medium in patients undergoing pulmonary angiography.

RATIONALE AND OBJECTIVES.The degree to which pulmonary angiography may contribute to serious complications in patients with pulmonary hypertension has not been clarified and remains a matter of debate. Accordingly, this study was designed (1) to detect the potential release of vasoactive peptides and (2) to investigate the hemodynamic response after administration of a nonionic contrast medium in patients with pulmonary hypertension undergoing pulmonary angiography. Allergy-mediating substances also were measured to monitor for possible anaphylactoid reactions. METHODS.Pulmonary digital subtraction angiography was performed in 20 patients with pulmonary hypertension (mean pulmonary arterial pressure more than 20 mm Hg). Iopromide was administered as a total of 100 mL via a 7F catheter inserted from the right femoral vein. The injected volume and duration of injection (15 to 20 mL/sec) were kept constant. Hemodynamic parameters were continuously monitored, including electrocardiogram, heart rate, phasic and mean pulmonary arterial and peripheral arterial pressures. Blood samples were obtained before and after administration of contrast media to assay for the concentration of the following vasoactive peptides using radioimmunoassay techniques: renin, angiotensin-I-converting enzyme, angiotensin II, aldosterone, atrial natriuretic peptide, antidiuretic hormone, cyclic-guanosine monophosphate, and myoglobin, as well as allergy-mediating substances such as tryptase, eosinophil protein X, and eosinophil cationic protein. RESULTS.Administration of iopromide caused significant increases in atrial natriuretic peptide (from 61.3 ± 11.8 to 94.0 ± 16.7) and antidiuretic hormone (from 6.6 ± 1.9 to 12.3 ± 3.1), whereas renin significantly decreased (from 3.0 ± 0.6 to 1.3 + 0.5). After administration of contrast media, there were no significant changes in the other measured vasoactive peptides, allergy-mediating substances, and monitored cardiovascular parameters. CONCLUSION. Administration of iopromide for pulmonary angiography in patients with pulmonary hypertension resulted in no appreciable hemodynamic alterations associated with the observed changes in atrial natriuretic peptide, antidiuretic hormone, and renin. No allergy-mediated reactions were observed in these patients.

Contrast-enhanced MR imaging of two superparamagnetic RES-contrast agents: functional assessment of experimental radiation-induced liver injury.

The purpose of this study was to compare liver contrast‐enhancing characteristics of two superparamagnetic reticuloendothelial system (RES)‐directed agents with different particle sizes, polycrystalline iron oxide nanocompounds (PION) and carboxydextran‐coated maghemite (DDM128N/389, later referred to as DDM128), in an experimental model of focal radiation‐induced hepatitis. PION, for the small particle size (31 nm), and DDM128, for the large particle size (59 nm), RES‐directed agents were compared for liver enhancement after radiation‐induced liver injury. A single x‐irradiation exposure varying from 10 to 60 Gy was delivered to one side of the liver. T2‐weighted spin‐echo magnetic resonance imaging was performed 3 days after x‐irradiation at 30 minutes post‐contrast. Using the RES‐directed PION, the normal, non‐irradiated portion of the liver decreased in signal intensity with a maximum negative enhancement of −66%, while the irradiated portion of the liver decreased in signal intensity by −24% (60 Gy). The signal intensity decline of irradiated liver tissue using PION was dose dependent, but was found at all radiation dose levels (10–60 Gy). The difference in signal intensity between irradiated (−63%) and non‐irradiated (−82%) portions was also statistically different using DDM128 at 60 Gy. However, lower irradiation doses (10 and 30 Gy) failed to produce a statistically significantly different enhancement in the irradiated and non‐irradiated portion of the liver. Sensitivity of liver enhancement with RES‐directed agents is size dependent. The smaller particle (PION) is more sensitive for detection of radiation‐induced hepatitis than the larger particle (DDM128). The relative insensitivity of DDM128 enhancement for diffuse liver injury will be clinically advantageous for detecting focal lesions in the presence of diffuse hepatic injury.J. Magn. Reson. Imaging 1999;10:52–56.

Kinetics of MRI Contrast Agents with a Size Ranging Between Gd-DTPA and Albumin-Gd-Dtpa Use of CASCADE-Gd-DTPA-24 Polymer

A unified kinetic theory describing the dynamic properties of magnetic resonance imaging (MRI) contrast agents with a size ranging between that of Gd-DTPA and albumin-(Gd-DTPA)30 was developed and tested in disease models of cancer and myocardial reperfusion injury. Specifically, a two-compartment kinetic model was solved analytically, and a range of special cases of the model was studied. MRI was performed with strongly T1-weighted sequences before and dynamically after administration of albumin-(Gd-DTPA)30, a prototype macromolecular contrast medium (MMCM) designed for blood-pool enhancement; a new MMCM: Gd-DTPA-cascade polymer (Schering AG, Berlin, Germany, MW < 30 kDa); or Gd-DTPA, representing small paramagnetic extracellular agents. The greatest dynamic range of contrast-agent sensitivity to disease was found for albumin-(Gd-DTPA)30.

Quantification of Area at Risk during Coronary Occlusion and Reperfusion by Means of MR Perfusion Imaging

Purpose: Considerable clinical interest has focused on the size of ischemic myocardium. Fast MR imaging in conjunction with MR contrast media has the potential to identify hypoperfused and infarcted myocardium. This study used MR perfusion imaging to detect and quantify reperfused ischemic myocardium during a brief coronary occlusion and reperfusion, and to characterize the spatial extent of ischemic and reperfused ischemic myocardium relative to the “true” size of the area at risk as defined in histochemical morphometry at post mortem. Material and Methods: The left circumflex (LCX) coronary artery in 8 dogs was occluded for 15 min followed by reperfusion in order to produce regional reversible myocardial ischemia. Perivascular Doppler probes were used to measure blood flow in the left anterior descending (LAD) and LCX coronary arteries. Fast inversion recovery-prepared gradient-recalled-echo images were acquired to delineate the ischemic area during occlusion, and the area of reversible ischemic injury at 1 and 30 min of reperfusion. The size of ischemic and reperfused ischemic myocardium were compared with the area at risk as determined by histochemical morphometry at post mortem. Results: During LCX occlusion, LCX flow decreased from 16±1 to 0.2± 0.1 ml/min. On contrast-enhanced images, ischemic myocardium was evident as a zone of relatively low signal intensity (SI) compared to normal myocardium. The size of the ischemic region was significantly smaller (30± 2%) than atpost mortem (36± 3%; p<0.05). Immediately after reperfusion, LCX flow increased to 83±11 ml/min and the contrast medium caused greater enhancement in the reperfused ischemic region than in the normal myocardium (69± 3 vs 42± 3 arbitrary units; p<0.05). The increase in regional SI correlated closely with the increase in regional blood flow (r=0.73). At 1 min of reperfusion, the size of the reperfused ischemic myocardium was larger (48± 3%, p<0.05) than the area at risk measured at post mortem. At 30 min of reperfusion, when the flow returned to baseline values (16± 2 ml/min), contrast bolus produced no differential enhancement between the 2 myocardial territories. Conclusion: MR perfusion imaging has the potential to detect and quantify the size of ischemic myocardium and the region of post-occlusive hyperemia in the early reperfusion period. There is a significant direct linear relationship between the regional contrast enhancement of reperfused ischemic myocardium and the blood flow during post-occlusive hyperemia. The difference in the size of the area at risk at MR perfusion imaging and at histochemical morphometry may reflect an influence of coronary collateral circulation.