Segmental disorders of the nephron: histopathological and imaging perspective.

Recent advances in molecular genetics and immunocytochemistry have clarified the cell of origin in many renal disorders. Several renal disorders are thought to involve specific segments of the nephron. Renin-secreting tumours arise from juxtaglomerular cells. Clear cell and papillary renal cell carcinoma (RCC) recapitulate the epithelium of the proximal tubules. Oncocytoma and chromophobe RCC differentiate towards Type A and Type B intercalated cells of the cortical collecting duct, respectively. Medullary collecting ducts are the target sites for the development of autosomal recessive polycystic kidney disease, collecting duct carcinoma and medullary carcinoma. Renal papillae are susceptible to unique changes such as necrosis or papillitis. The purpose of our article is threefold: to illustrate the imaging findings of renal disorders that show segmental involvement of the nephron, to describe proximal and distal nephron disorders and to correlate imaging findings of some entities with histopathological features.

Laparoscopic and computed tomography-guided percutaneous radiofrequency ablation of renal tissue: acute and chronic effects in an animal model.

OBJECTIVES: To evaluate the laparoscopic and percutaneous delivery of impedance-based radiofrequency ablation (RFA) of the kidney by studying the acute and chronic clinical, radiographic, and histopathologic effects in the porcine model. METHODS: Eight kidneys from 4 pigs underwent laparoscopic RFA. Six kidneys from 3 additional pigs received computed tomography (CT)-guided, percutaneous RFA. CT scans were performed immediately after RFA and before harvest at 2 hours, 24 hours, 3 weeks, and 13 weeks. The gross, radiographic, and histopathologic changes were recorded for each period. RESULTS: Grossly, the RFA lesions were sharply demarcated, measuring 3 to 5 cm. Two major complications (14%) occurred (one urinoma, one psoas muscle injury) in 14 ablations. No deaths or significant blood loss occurred as a result of RFA. Radiographically, the immediate CT scanning demonstrated small perinephric hematomas and wedge-shaped defects. Delayed CT showed nonenhancing defects up to 5 cm. Color-flow and power Doppler were unable to distinguish significant tissue changes during RFA. The histopathologic evaluation revealed marked inflammation surrounding the necrotic regions in the early lesions; chronic lesions were characterized by dense fibrosis. The tissue temperatures ranged from 62 degrees to 118 degrees C in the area of ablation. CONCLUSIONS: RFA is readily delivered laparoscopically or percutaneously with minimal morbidity. Impedance-based application of radiofrequency energy allows monitoring and control of ablation. Using a multi-antenna probe, areas of tissue up to 5 cm can be completely destroyed. The RFA lesion can be monitored as a nonenhancing cortical defect on CT.

Appendiceal CT in pediatric patients: relationship of visualization to amount of peritoneal fat.

OBJECTIVE: This study was performed to determine the rate of visualization of the normal pediatric appendix on CT and to evaluate the relationship of the appendix to parameters such as amount of intraperitoneal fat, use of contrast material, patient age, and slice thickness. MATERIALS AND METHODS: Three board-certified radiologists retrospectively reviewed 248 successive pediatric abdominal and pelvic CT examinations performed from 1995 to 1999. Each radiologist independently assessed the degree of intraperitoneal fat (minimal, moderate, or marked compared with a standard slice), appendiceal visualization (definite, unsure, not seen), cecal and terminal ileal opacification, and the outer diameter of visualized appendixes. The age and sex of the patient, collimation thickness (3-10 mm), and use of enteric or IV contrast material was also recorded. RESULTS: A normal appendix was identified in 120 (48.4%) of 248 examinations. The only individual variable with statistically significant correlation was the degree of intraperitoneal fat. This was determined using the Pearson chi-square test, the likelihood ratio, and logistic regression. The appendix was seen in 68.8% (n = 93) of patients with moderate or marked intraperitoneal fat versus 36.1% (n = 155) with minimal fat (p<0.001). A trend toward decreased visualization in children younger than 10 years old with minimal peritoneal fat was identified and confirmed with a 95% confidence limit. The outer diameter of the visualized appendix varied from 3 to 10 mm, with a mean value of 6 mm. CONCLUSION: Increased peritoneal fat significantly increases the rate of identification of the normal appendix in pediatric patients. Although less fat is generally seen in younger patients, there is significant overlap of appendix visualization among age groups.

Pearls and pitfalls in the diagnosis of ureterolithiasis with unenhanced helical CT.

Several signs to assist interpretation of unenhanced helical computed tomographic (CT) scans obtained for suspected ureterolithiasis have been described. Because signs such as perinephric stranding are not always readily apparent, a methodical approach to interpretation of CT studies is important in determining the presence or absence of ureterolithiasis. Evaluation of the poles of the kidneys is helpful in detecting subtle stranding of the perinephric fat. Inspection of the intrarenal collecting system within the poles of the kidneys is helpful in identifying subtle collecting system dilatation and can help prevent mistaking an extrarenal pelvis for hydronephrosis. Careful inspection of the ureter throughout its course is the most reliable method of distinguishing between ureteral stones and phleboliths. However, when the ureter cannot be followed antegrade, the pelvic portion can often be identified in a retrograde fashion. When secondary signs of obstruction are present but no stone is present, differential diagnostic considerations include a recently passed stone, pyelonephritis, urinary tract obstruction unrelated to stone disease, and protease inhibitor deposition disease.

Acute flank pain: a modern approach to diagnosis and management.

Acute flank pain is a common and complex clinical problem. In addition to flank pain caused by ureterolithiasis, other urinary and extraurinary abnormalities can result in a similar clinical picture. Unenhanced CT can rapidly, accurately, and safely determine the presence or absence of ureteral obstruction. When obstruction is caused by ureterolithiasis, CT allows precise determination of stone size and location. These are the two most important factors used for patient management. In addition to direct stone visualization, there are many secondary CT signs of ureteral obstruction that are direct manifestations of the underlying pathophysiology. On the other hand, when obstruction is absent, CT can diagnose or exclude most other abnormalities that result in flank pain. As a result of its many advantages, unenhanced helical CT should become the dominant imaging modality for evaluation of all patients with acute flank pain in whom a clinical diagnosis is uncertain.

The value of unenhanced helical computerized tomography in the management of acute flank pain.

PURPOSE: We developed an algorithm using unenhanced computerized tomography (CT) for the management of acute flank pain and suspected ureteral obstruction. MATERIALS AND METHODS: During a 25-month interval 417 patients with acute flank pain underwent unenhanced helical CT. The final diagnosis was confirmed by additional imaging or clinical followup. For all patients who underwent additional imaging studies the official dictated radiology reports were used to determine whether the studies were recommended based on CT findings. Cases requiring intervention were evaluated to determine whether additional imaging was performed before the procedure. Medical records were reviewed and/or patients were interviewed to document the course of therapy and long-term outcome. RESULTS: Unenhanced helical CT diagnosed ureteral stone disease with 95% sensitivity, 98% specificity and 97% accuracy. Of the 38 patients requiring intervention, including nephrostomy catheters in 18, lithotripsy in 3 and ureteroscopic stone extraction in 7, additional imaging (excretory urography) was performed in only 1. Additional imaging studies generated by CT were done in 3 cases in which the dictated reports were indeterminate for ureteral stones, including negative excretory urography in 2 and retrograde urography in 1. In 1 patient in whom CT misdiagnosed a ureteral stone unnecessary retrograde urography revealed the calcification to be a gonadal vein phlebolith. Seven patients with false-negative examinations reported spontaneous stone passage with no complications. CONCLUSIONS: Unenhanced helical CT accurately determines the presence or absence of ureterolithiasis in patients with acute flank pain. CT precisely identifies stone size and location. When ureterolithiasis is absent, other causes of acute flank pain can be identified. In most cases additional imaging is not required.

Soft-tissue "rim" sign in the diagnosis of ureteral calculi with use of unenhanced helical CT.

PURPOSE: To determine the value of the ureteric soft-tissue "rim" sign for differentiation of ureteral calculi from phleboliths on unenhanced helical computed tomographic (CT) scans and to identify factors that are associated with the presence of the rim sign. MATERIALS AND METHODS: Of 442 patients with ureteral obstruction confirmed at CT, 200 had documented ureteral stone disease; 136 of these patients had ureteral calculi, excluding the ureterovesical or ureteropelvic junctions. Each calculus and phlebolith along the course of the ureter were evaluated retrospectively and blindly for the presence of the rim sign, stone location, and stone size; the duration of symptoms was documented when available. RESULTS: The rim sign was present in 105 of 136 ureteral calculi (77%) and in 20 of 259 phleboliths (8%) and yielded a sensitivity of 77% and a specificity of 92% for distinguishing a calculus from a phlebolith. Calculi associated with the rim sign had a mean size of 4.3 mm, and calculi without a rim sign had a mean size of 6.3 mm (P < .001). There was no difference in duration of symptoms among patients who did or did not exhibit a rim sign. CONCLUSION: In patients with flank pain, the presence of a rim sign is a strong indicator that a calcification along the course of the ureter is a stone. Absence of the rim sign indicates that a calcification remains indeterminate.