Hyperdense renal masses: a CT manifestation of hemorrhagic renal cysts

A Practical Approach to Indeterminate and Cystic Renal Masses

Cystic renal masses are a common entity with a wide differential diagnosis encountered by the radiologist in daily practice. Their characterization relies on the Bosniak classification system that has been widely accepted by radiologists and urologists as a pertinent diagnostic and communication tool. It has been designed to separate cystic lesions requiring surgery (categories III and IV) from those that can be ignored and left alone (categories I and II) or followed (category IIF). Utilization of the Bosniak classification requires, first, previous identification of the cystic nature of a renal mass with the exception of very small lesions.

Multilocular cystic renal cell carcinoma: clinicopathological features and preoperative prediction using multiphase computed tomography

OBJECTIVE

• To analyse the clinicopathological and radiological features of multilocular cystic renal cell carcinoma (MCRCC) and to determine the preoperative factors differentiating MCRCC from other cystic RCC (CRCC).

PATIENTS AND METHODS

• The medical records of 53 patients with complex cystic renal masses evaluated by multiphase computed tomography (CT), surgically removed and confirmed as sporadic RCC were reviewed. • Of these 53 patients, 23 were classified as having MCRCC and 30 as other CRCCs, defined as RCCs with extensive cystic change or cystic necrosis. • Another 22 patients were treated for complex cystic renal masses presumed to be RCC and diagnosed as having benign cyst.

RESULTS

• Benign cysts and MCRCCs were significantly more likely to be of Bosniak classification III than other CRCCs (77% vs 61% vs 27%, P= 0.001). • The mean Hounsfield unit (HU) during the corticomedullary phase (CMP) was significantly higher in other CRCCs, with HU ≥38 having 83% sensitivity and 80% specificity for predicting other CRCCs. • In a multiple regression model, Bosniak classification and mean HU during CMP were independent factors predictive of other CRCCs. • In the 41 patients with masses >4 cm in diameter, the combination of Bosniak classification IV and HU ≥38 during CMP showed 63% sensitivity, 96% specificity, 91% positive predictive value and 80% negative predictive value, yielding 2% false-positive and 15% false-negative rates.

CONCLUSIONS

• The mean HU during CMP and Bosniak classification can differentiate MCRCC from other CRCCs. • This could help in selecting an appropriate surgical method, such as nephron-sparing surgery, for complex cystic renal masses >4 cm.

[Imaging characterization of renal masses. Image atlas]

The diagnostic study, analysis and characterization of renal masses and their behavior is one of the key elements for elaborating a surgical or therapeutic strategy, determining the prognosis, and for the follow-up of treatment efficacy in patients with benign or malignant disease. At present, computed tomography (CT) and magnetic resonance imaging (MRI) are the two most reliable, effective and efficient instruments in this context--offering sensitivity and specificity values in excess of 87%, with a diagnostic relaibility of over 90% in application to renal masses of a cystic or complex nature, with nonspecific or specific inflammatory characteristics, or of a primary or secondary neoplastic nature. The aim of this study is to present the principal CT and MRI parameters in relation to renal pathology of this kind, correlating them to the clinical, physiopathological and histopathological data with a view to affording architectural, density, signal intensity and biological behavior parametric information of help in understanding the changes occurring in the renal and retroperitoneal regions secondary to such pathologies.

Hyperattenuating renal masses: etiologies, pathogenesis, and imaging evaluation

Some renal masses have higher attenuation than the surrounding renal parenchyma at computed tomography (CT). Their hyperattenuation is usually the result of proteinaceous fluid or densely packed cells. Most hyperattenuating renal masses are benign hemorrhagic or proteinaceous cysts. However, solid enhancing hyperattenuating renal masses may have malignant as well as benign causes. Possible malignant causes include renal cell carcinoma and lymphoma; benign causes include angiomyolipoma with minimal fat. It is important to identify the cause of a hyperattenuating renal mass so as to avoid unnecessary surgical resection or ablation. CT may be useful for diagnosing benign hyperattenuating renal cysts, hematomas, and vascular anomalies that appear masslike. However, some solid, enhancing, hyperattenuating masses cannot be diagnosed confidently with CT alone: Small (< or = 3-cm-diameter), homogeneously enhancing, hyperattenuating renal masses depicted on CT images may be either benign angiomyolipomas with minimal fat or renal cell carcinomas. Magnetic resonance (MR) imaging may be helpful for differentiating between angiomyolipomas with minimal fat and clear cell renal cell carcinomas; however, differentiation between angiomyolipomas with minimal fat and papillary renal cell carcinomas often is not possible on the basis of MR imaging. In such cases, a percutaneous biopsy may be useful for diagnosis. If the results of MR imaging and percutaneous biopsy are not definitive, surgery is warranted.

Can High-Attenuation Renal Cysts Be Differentiated from Renal Cell Carcinoma at Unenhanced CT?

PURPOSE

To retrospectively determine if renal cell carcinoma can be differentiated from high-attenuation renal cysts at unenhanced computed tomography (CT) based on Hounsfield unit measurements and heterogeneity.

MATERIALS AND METHODS

The Human Investigation Committee at our institution approved this study with waiver of informed consent. This study was compliant with the HIPAA. Fifty-four pathologically proved renal cell carcinomas in 54 patients (36 men and 18 women; average age, 53 years; range, 23-90 years) and 56 high-attenuation renal cysts in 51 patients (30 men and 21 women; average age, 63 years; range, 28-86 years) were retrospectively evaluated at unenhanced CT. Two independent readers reviewed randomized unenhanced CT images and obtained Hounsfield unit readings of each mass. A subjective determination of lesion heterogeneity was also performed by using a four-point scale (1: homogeneous, 2: mildly heterogeneous, 3: moderately heterogeneous, 4: markedly heterogeneous). Statistical analysis was performed by using Bland-Altman regression tree, classification and regression tree, and Shapiro-Wilk normality test.

RESULTS

The average attenuation of cysts for reader 1 was 53.4 HU (range, 23-113 HU) and for reader 2 was 53.8 HU (range, 21-108 HU). The average attenuation of neoplasms for reader 1 was 34.7 HU (range, 21-60 HU) and for reader 2 was 38.4 HU (range, 22-60 HU). For cyst heterogeneity, a score of 1 was given in 55 of 56 (98%) cysts for reader 1 and in 53 of 56 (95%) cysts for reader 2. For neoplasm heterogeneity, a score of 1 was given in 35 of 54 (65%) neoplasms for reader 1 and in 36 of 54 (67%) for reader 2. Given the distribution of cyst and tumor attenuation values and lesion heterogeneity, a homogeneous mass measuring 70 HU or greater at unenhanced CT has a greater than 99.9% chance of representing a high-attenuation renal cyst.

CONCLUSION

The findings from this study may help differentiate high-attenuation renal cysts from renal cell carcinomas at unenhanced CT and may suggest the next appropriate imaging study for definitive characterization.

Differentiation of Renal Neoplasms From High-Density Cysts

PURPOSE

The current study evaluated attenuation changes for proven renal neoplasms between the corticomedullary and the nephrographic phases of a contrast-enhanced computed tomographic (CT) scan as a possible means for differentiating these tumors from the cysts of the kidney when high-density renal masses are detected on a CT scan that does not include a noncontrast baseline.

METHODS

We retrospectively reviewed the CT scans performed on 20 patients with 21 biopsy-proven renal neoplasms, which had been done using standard contrast-enhanced computed tomography only. Attenuation values for the 21 renal neoplasms and for 23 simple cysts, used as an internal control, were measured and recorded from the 2 phases of enhancement. The difference in attenuation between the 2 phases of enhancement for each mass was calculated. Data for the neoplasms and cysts were compared with published data for enhancement changes for proven high-density renal cysts.

RESULTS

The mean absolute value change in attenuation between the corticomedullary and the nephrographic phases for renal neoplasms was 22 Hounsfield units (HU) (range, 1.0-48 HU) and 1 HU (range, 0.1-3.3 HU) for simple cysts. Only one renal neoplasm (5%) changed to less than 10 HU.

CONCLUSIONS

Almost all renal neoplasms studied had an attenuation change of more than 10 HU, either increased or decreased, between 2 phases of a contrast-enhanced CT scan separated by 50 seconds. The results suggest that if the attenuation of a renal tumor changes by more than 10 HU between phases of a contrast-enhanced computed tomography, then the diagnosis of renal neoplasm is very likely. High-attenuation renal masses which change less than 10 HU between the corticomedullary and tubular phases are most likely high-density cysts, but neoplasm is possible.

Distinction of renal cell carcinomas from high-attenuation renal cysts at portal venous phase contrast-enhanced CT

PURPOSE

To determine if renal cell carcinomas can be distinguished from high-attenuation renal cysts on portal venous phase contrast material-enhanced computed tomographic (CT) scans.

MATERIALS AND METHODS

Fifty-seven renal cell carcinomas and 37 high-attenuation (>20 HU) renal cysts that were at least 1 cm in diameter were retrospectively identified in 90 patients who underwent portal venous phase contrast-enhanced CT. Two independent readers recorded the CT number and degree of internal heterogeneity (uniform or mildly, moderately, or markedly heterogeneous) of all lesions. Logistic regression analysis with adjustment for the two readers was used to examine the association between clinical and CT parameters and the final diagnosis. Stepwise logistic regression analysis was used to identify independent distinguishing variables, which were then incorporated in a classification and regression tree analysis to construct the most efficient classification algorithm.

RESULTS

Renal cell carcinomas were of significantly greater size (5.10 cm vs 2.84 cm, P <.001), mean attenuation (101.2 HU vs 55.3 HU, P <.001), and internal heterogeneity (P <.001) than high-attenuation renal cysts. Stepwise logistic regression showed attenuation and internal heterogeneity were both independent variables associated with final diagnosis, but lesion size was not an independent distinguishing variable after adjustment for internal heterogeneity. Classification and regression tree analysis demonstrated that an attenuation greater than 70 HU or the presence of moderate or marked internal heterogeneity was an accurate sign of renal cell carcinoma, with a sensitivity of 91% (52 of 57) for both readers and a specificity of 92% (34 of 37) for reader 1 and 84% (31 of 37) for reader 2.

CONCLUSION

On portal venous phase contrast-enhanced CT scans, attenuation greater than 70 HU or moderate or marked internal heterogeneity favor a diagnosis of renal cell carcinoma over a diagnosis of high-attenuation renal cyst.

Delayed CT to evaluate renal masses incidentally discovered at contrast-enhanced CT: demonstration of vascularity with deenhancement

PURPOSE

To determine whether delayed computed tomography (CT) can help confirm vascularity in a neoplasm and differentiate it from a high-density cyst when a well-demarcated homogeneous high-attenuating (> 30-HU) renal mass is incidentally discovered during contrast material-enhanced CT.

MATERIALS AND METHODS

In 25 patients, 26 well-demarcated, homogeneous high-attenuating renal masses (mean diameter, 2.5 cm; range, 1-4 cm) detected at initial postcontrast CT were further evaluated with delayed CT (mean, 38 minutes; range, 15-240 minutes) performed with identical parameters. On both the initial postcontrast and delayed CT scans, region-of-interest measurements were obtained in renal masses and in the gallbladder or low-density renal cysts as controls. Correlation with surgical or additional imaging findings was used to determine proof of diagnosis.

RESULTS

Nine of the masses demonstrated no change in attenuation between initial postcontrast and delayed CT, indicating that they represented avascular lesions consistent with high-density cysts. These cases were confirmed with prior or follow-up imaging studies that demonstrated stability. Seventeen masses (nine surgically proved neoplasms and eight neoplasms that demonstrated interval growth at follow-up or previous CT) demonstrated decreased attenuation at delayed CT compared with initial postcontrast CT, which indicates vascularity.

CONCLUSION

Delayed CT of incidentally discovered well-demarcated homogeneous high-attenuating (> 30-HU) renal masses detected at postcontrast CT enables differentiation of high-density cysts from renal neoplasms by demonstrating deenhancement as a proof of vascularity and, hence, neoplasm.

Radiologic evaluation of small and indeterminant renal masses

A common problem in radiologic and urologic practice today is what to do with the small or indeterminant renal mass. Whether found incidentally or sought after because of patient symptomatology, these lesions present a challenge in diagnosis and management. This article outlines the scope of the problem, illustrates representative lesions, suggests imaging and management strategies culled from personal experience, and provides a review of available literature.

Cross-sectional imaging of idiopathic solitary renal vein varix: report of two cases

Two cases of solitary renal vein varices are reported which presented as incidental findings on abdominal computed tomography (CT) and were initially thought to represent retroperitoneal lymph nodes. Contrast-enhanced CT, magnetic resonance imaging (MRI), and Doppler ultrasound (US), all demonstrated the vascular nature of these masses suggesting the correct diagnosis. When a rounded soft tissue density mass is seen on noncontrast-enhanced CT either in or contiguous to the renal hilum, a renal vein varix must be excluded. Doppler US, MRI, or dynamic contrast-enhanced CT should be done to exclude a renal varix as the cause.

Cystic renal masses: usefulness of the Bosniak classification

To determine the usefulness of the Bosniak classification of cystic renal masses, the computed tomographic (CT) and ultrasound findings of 16 pathologically proven cystic renal masses were retrospectively reviewed. All imaging studies were reviewed and categorized utilizing the Bosniak classification without knowledge of the final pathologic diagnosis. There were no category I lesions (classical simple cyst), four category II (minimally complicated), seven category III lesions (more complicated), and five category IV lesions (probable malignant). All category II lesions were benign, all category IV lesions were malignant. Of the seven category III lesions, three were benign and four were malignant. We conclude that the Bosniak classification is extremely useful in the management of cystic renal masses.

Hyperdense renal cyst due to prolonged retention of iodinated contrast material: case report

A case of a hyperdense renal cortical cyst resulting from cyst puncture and opacification 28 months previously is reported. Prolonged retention of water-soluble iodinated contrast material is an unusual cause of a hyperdense renal cyst, which has not previously been described. The findings on serial computed tomography (CT) and chemical analysis are presented and discussed.

Problematic renal masses in ultrasonography and computed tomography

The diagnosis of renal masses is based upon the contribution of ultrasonography (US) and computed tomography (CT), which enable the recognition of these lesions with high diagnostic accuracy. However, a number of diagnostic difficulties exist in the definition of the nature of the mass, both for cystic and solid lesions, and to a lesser extent in the identification of the mass. "Complicated" cystic masses, such as calcified cysts, hemorrhagic cysts, inflammatory cysts, abscesses, and cystic tumors may be difficult to diagnose with US and sometimes with CT. CT is helpful in most of these cases because it enables the evaluation of the calcifications and the density of the fluid content. CT is also helpful in cases of cystic tumors because it shows the enhancement of septae within the masses. Problems with solid masses are the identification of small renal tumors and the definition of the benign or malignant nature of the mass. Although both techniques enable the recognition of most tumors, even if small in diameter, they are still limited in defining the pathological structure of the tumor.

Sonography of small renal masses with indeterminant density characteristics on computed tomography

Nine small renal masses with attenuation coefficients greater than 20 HU on computed tomography (CT) were termed indeterminate for cyst or renal cell carcinoma. Correlative sonography identified the fluid-filled internal architecture in four of five cysts and correctly characterized as solid four small renal cell carcinomas. The sonogram was particularly valuable in assessing masses that were indeterminate on CT when enhancement was equivocal or when intravenous contrast could not be administered. We conclude that sonography is extremely useful as a noninvasive procedure in evaluating the occasional small renal mass with CT number greater than 20 HU.

Renal adenocarcinoma in benign hyperdense mass

We report a case of a renal adenocarcinoma presenting as a benign hyperdense mass. The etiology and radiologic diagnosis of hyperdense renal masses are presented.

Computed tomographic and ultrasound appearances of a solitary intrahepatic choledochal cyst

A pregnant patient presenting with acute abdominal pain was found to have an intrahepatic mass, the features of which, on computed tomography and ultrasound examination, suggested a solid lesion. At surgery this proved to be a solitary intrahepatic choledochal cyst (Todani Type 5) with areas of malignant degeneration.