Assessment of the clinical utility of the rim and comet-tail signs in differentiating ureteral stones from phleboliths.

OBJECTIVE: This study was designed to assess interobserver variability in identifying the rim and comet-tail signs and to determine the clinical utility of these signs in determining whether or not the calcifications with which they are associated represent ureteral calculi. MATERIALS AND METHODS: Two radiologists and a radiology resident, unaware of the final diagnosis, reviewed preselected helical CT images from renal stone examinations in patients with 65 indeterminate pelvic calcifications. Assessment of calcifications for rim or comet-tail signs was performed independently of an assessment for the following five secondary signs of urinary tract obstruction: caliectasis, pelviectasis, ureterectasis, perinephric stranding, and renal enlargement. Agreement in identifying rim and comet-tail signs was assessed by obtaining kappa statistics. The utility the of rim or comet-tail signs in determining whether ureterolithiasis was present in patients in whom perinephric stranding and ureterectasis were present or absent was determined. The frequency with which one or more of each of the five assessed secondary signs was identified ipsilateral to a calcification having rim or comet-tail signs was also tabulated. RESULTS: Kappa values for interobserver agreement ranged from 0.49 to 0.73. In only one patient was a rim sign detected in the absence of ureterectasis and perinephric stranding. Reviewers identified at least three of the five assessed secondary signs ipsilateral to calcifications showing a rim sign in all but one patient (by each radiologist) and four patients (by the resident). When three or more secondary signs of obstruction were seen ipsilateral to a calcification having a comet-tail sign, in all but one instance, this was because the calcification was a ureteral calculus or because there was a separate ipsilateral ureteral calculus. CONCLUSION: In many instances, observers did not agree about whether the rim and comet-tail signs were present. The rim sign was observed in the absence of any secondary signs of urinary tract obstruction in only one (1.5%) of the 65 patients in our series (95% confidence interval, 0-5.3%). The comet-tail sign, when accompanied by secondary signs of obstruction, should indicate that an ipsilateral ureteral stone is present and not the reverse.

Dentate nuclei involvement in AIDS patients with CNS cryptococcosis: imaging findings with pathologic correlation.

PURPOSE: Our goal was to describe the involvement of the dentate nuclei in AIDS patients with CNS cryptococcosis since this finding has not been emphasized in previous radiological literature. METHOD: Plain and contrast-enhanced CT of the brain (10 and 10), MR studies (1 premortem and 1 postmortem), and autopsy findings in 11 AIDS patients with CNS cryptococcosis were reviewed. The imaging studies and pathological specimens were analyzed for signs of meningitis, presence of dilated Virchow-Robin spaces, gelatinous pseudocysts, cryptococcoma, ventriculomegaly, choroid plexus, and ependymal lesions. RESULTS: Five of 11 patients were found at autopsy to have macroscopically visible "cystic" lesions in the dentate nuclei that were not detected on CT (10 patients), but were seen on premortem MR (1 patient). Macroscopic supratentorial (basal ganglia, thalamic, midbrain) lesions were detected by CT in 5 of 11 patients and by MR in 2 of 2 patients. Enhancement of the leptomeninges was seen in only 1 patient by CT despite pathological evidence of cryptococcal meningitis in all 11 patients. Dilated Virchow-Robin spaces were seen in all 11 pathologic specimens and in the 2 MR studies but not on CT. Communicating hydrocephalus was detected by CT in two patients. CONCLUSION: CT scans of the brain underestimate infratentorial parenchymal cryptococcal disease. MR is a more sensitive procedure to evaluate cerebellar and brainstem cryptococcosis, including the dentate nuclei, which in our autopsy series was not an uncommon site to be infected with cryptococcal gelatinous pseudocysts.