Cystic renal disease

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1 Magn Reson Imaging Clin N Am 12 (2004) Cystic renal disease Fadi M. EL-Merhi, MD, Kyongtae T. Bae, MD, PhD* Mallinckrodt Institute of Radiology, Washington University School of Medicine, 510 South Kingshighway Boulevard, St. Louis, MO 63110, USA Renal cysts are relatively common radiographic and clinical abnormalities. Cystic renal disease is a heterogeneous entity comprised of heritable, developmental, and acquired disorders. During the last decade, considerable progress has been made in reaching a consensus for standard terminologies and classifications of cystic renal disease among radiologists, pathologists, nephrologists, and urologists, as shown in Box 1 [1]. Some of these entities are exceedingly rare and beyond the scope of this article. Diagnosis of a specific cystic renal disease often is made from the clinical history of the patient combined with radiographic findings. MR imaging has been used mainly to assess complications associated with renal cysts, such as infection or bleeding, or to differentiate benign from malignant cystic lesions. MR imaging provides high-resolution three-dimensional (3D) images with excellent tissue contrast to facilitate the characterization and evaluation of renal cysts and cystic lesions. MR imaging has an advantage over CT because iodinated contrast agents, which are required frequently in CT to characterize renal cystic lesions, cannot be used in many patients with cystic renal disease who are associated often with renal functional impairment. MR imaging also has proven useful for the evaluation of morphologic and physiologic changes associated with cystic renal disease [2 4]. MR imaging technique Intravenous gadilinium chelate is used commonly in renal MR examinations. In the patient * Corresponding author. address: baet@mir.wustl.edu (K.T. Bae). preparation area, an antecubital angiocatheter is placed before the initiation of the examination. The vein is kept open with a slow infusion of normal saline. Patients are placed supine on the MR imaging table with their hands on the side. The use of a phased-array body surface coil is preferred highly to a body coil to improve the signalto-noise ratio. A small field of view is recommended, approximately 300 to 350 mm in most patients. At the authors institution, standard renalimaging protocol starts with a variable localizer sequence. This is followed by the following breath-hold sequences: half Fourier turbo spin echo sequence (HASTE) (single shot fast spin echo) coronal; gradient recalled-echo (GRE) inand opposed-phase axial; GRE T1-weighted with fat saturation (Fat Sat) axial; inversion recovery T2-weighted axial; HASTE Fat Sat axial, turbo spin echo (TSE) T2-weighted with and without Fat Sat axial; 3D volumetric interpolated breathhold examination (VIBE) (3D spoiled gradientecho [SPGE] with interpolation) precontrast axial and coronal; 3D VIBE dynamic postcontrast axial three times (capillary, interstitial, and equilibrium phases); and 3D VIBE postcontrast coronal. Simple, complex, and localized renal cysts Simple cysts are the most common benign renal lesions in adults [5]. They commonly arise in the cortex but may be located in the medulla. Renal cysts can be solitary, multiple, or bilateral [6]. Most are discovered incidentally on ultrasound or CT examinations [7,8]. Simple cysts are round and well demarcated from the adjacent renal parenchyma. They are filled with clear fluid and have imperceptible wall /04/$ - see front matter Ó 2004 Elsevier Inc. All rights reserved. doi: /j.mric

2 450 F.M. EL-Merhi, K.T. Bae / Magn Reson Imaging Clin N Am 12 (2004) Box 1. Classification of cystic renal disease I. Localized cystic disease A. Simple renal cysts, solitary and multiple B. Localized, segmental, and unilateral renal cysts II. Polycystic kidney disease A. Autosomal dominant polycystic kidney disease 1) Glomerulocystic disease of newborn 2) Classic polycystic disease of older children and adults a. Dominant polycystic disease linked to chromosome 16 b. Dominant polycystic disease not linked to chromosome 16 B. Autosomal recessive polycystic kidney disease 1) Polycystic disease of newborns and infants 2) Polycystic disease of older children and adults a. Medullary ductal ectasia b. Congenital hepatic fibrosis c. Caroli syndrome III. Renal cysts in hereditary malformation syndromes A. Tuberous sclerosis B. von Hippel-Lindau disease C. Zellweger cerebrohepatorenal syndrome D. Jeune asphyxiating thoracic dysplasia E. Oral-facial-digital syndrome I F. Brachyesomelia-renal syndrome IV. Glomerulocystic kidney disease A. Infantile-onset dominant polycystic kidney disease B. Syndromal glomerular cystic disease C. Nonsyndromal glomerular cysts V. Acquired renal cystic disease VI. Renal medullary cysts A. Medullary sponge kidney B. Hereditary tubulointerstitial nephritis 1) Familial juvenile nephronophthisis 2) Medullary cystic disease 3) Renal-retinal dysplasia complex VII. Renal cystic dysplasia A. Multicystic kidney B. Cystic dysplasia associated with lower urinary tract obstruction C. Diffuse cystic dysplasia, syndromal and nonsyndromal VIII. Extraparenchal renal cysts A. Parapelvic lymphangiectasia B. Perinephric cyst thickness, especially when they extend beyond the renal cortex. Simple renal cysts appear bright on T2-weighted images and maintain homogeneous signal void on pre- and postcontrast T1-weighted images with no demonstrable contrast enhancement (Fig. 1). The absence of contrast enhancement is critical to differentiate renal cysts from renal tumors. The optimal percentage of enhancement thresholds for distinguishing cysts from malignancies with MR imaging is reported to be 15%, with the optimal timing for measurement at 2 to 4 minutes after administration of contrast material [9]. Cysts may seem to enhance, however, because of multiple technical and image-related factors, termed pseudo-enhancement. In addition, renal parenchyma around the cyst may mimic a thick wall on some images, known as pseudothick wall sign. Simple cysts may be complicated by internal hemorrhage or infection and may present with

3 F.M. EL-Merhi, K.T. Bae / Magn Reson Imaging Clin N Am 12 (2004) Fig. 1. (A) Axial T1 in phase, (B) axial T2 inversion recovery (IR), and (C) axial VIBE Fat Sat post show bilateral, simple renal cyst with low T1 signal, high T2 signal, and no enhancement post contrast injection. complex radiologic features suggestive of cystic renal neoplasm. MR imaging has been used highly to solve the inconclusive complex cystic renal masses documented by either ultrasound or CT scan. Hemorrhage or protein may cause T1 shortening and thus increase the complexity of these cysts [10 12]. Most hemorrhagic cysts show high signal intensity on T1-weighted images and variable signal intensities on T2-weighted images, depending on the stage of blood products [10,13]. Some cysts may display a fluid-fluid level secondary to hematocrit effect (Fig. 2). The lack of enhancement and their sharp margination with the surrounding renal parenchyma are important imaging findings to document the benign nature of a cystic lesion. Often, a follow-up MR imaging study is required to document either evolution of the blood-product nature of hemorrhagic cysts or stability of proteinaceous cysts [14]. Complex renal cysts may have septations, thick walls, and calcifications. Septations less than 2 mm in renal cysts represent fibrin strands secondary to hemorrhage or infection or may represent two juxtaposed cysts. The uniformity in size and morphology and the lack of nodular-enhancing component of the septations indicate their benign nature (Fig. 3). The presence of calcium in the wall of renal cysts is difficult to identify on MR imaging, but calcium will not interfere in the evaluation of adjacent soft tissues [14]. Localized cystic disease is a cluster of small simple cysts localized in one portion of the kidney. It may be indistinguishable from a multilocular cystic nephroma. The absence of a capsule surrounding the cluster and the presence of cysts outside the cluster may help to diagnose localized cystic disease. Autosomal dominant polycystic kidney disease Autosomal dominant polycystic kidney disease (ADPKD) is the most common heritable renal disorder that is characterized by the development and enlargement of renal cysts involving the renal cortex and medulla. It occurs in 1:700 to 1:1000 individuals [15], affecting approximately 600,000

4 452 F.M. EL-Merhi, K.T. Bae / Magn Reson Imaging Clin N Am 12 (2004) Fig. 2. (A) Axial VIBE Fat Sat pre, (B) axial HASTE, and (C) axial VIBE Fat Sat post show a hemorrhagic cyst with fluid-fluid level secondary to hematocrit effect in the posterior midzone of the left kidney. Americans, and is the fourth-leading cause of endstage renal disease. ADPKD is a polygenic disorder, but most affected individuals (approximately 85%) have the PKD1 gene [16]. Both PKD1 and PKD2 genes have been identified and their structures determined. Gene type may predict disease severity; the PKD2 gene is associated with a milder phenotype and slower disease progression [17]. Characteristic imaging findings of ADPKD include enlarged kidneys with multiple cysts (Fig. 4). The kidneys are affected bilaterally in almost all instances, but may be quite asymmetric. Early in the disease a sizable amount of normal renal parenchyma is present, but with time the kidney becomes replaced completely by cysts and normal parenchyma is no longer identifiable. The kidney enlarges as the individual cysts grow and the number of cysts increases. Most cysts are simple cysts and have low signal intensity on T1- weighted images and prominently high signal intensity on T2-weighted images, but the signal intensity of complex cysts affected by hemorrhage or infection may vary. Hemorrhagic cysts are often multiple and subcapsular in location and common in kidneys with a heavy cyst burden. The signal intensity of hemorrhagic cysts is high on T1-weighted images and often low on T2-weighted images, but the T2 signal intensity may vary depending on the chronicity of the blood products (Fig. 5) [18]. Some cysts may show fluid-fluid level secondary to hematocrit effect. ADPKD is associated with many extrarenal, cystic, and noncystic manifestations [19]. Cysts in the liver are common in over 70% in women and older individuals (Fig. 6). Other organs that may contain cysts include pancreas (Fig. 7), spleen, epididymis, seminal vesicle, uterus, ovary, and thyroid. ADPKD may be associated with saccular berry aneurysm of the circle of Willis in 3% to 13% of patients [20], aortic dissection, cardiac valvular disease, and colonic diverticulosis. Common clinical presentations of ADPKD include abdominal pain, hematuria, and hypertension. Renal stones and infection are more common than in the normal population, but the risk for renal-cell carcinoma is not increased.

5 F.M. EL-Merhi, K.T. Bae / Magn Reson Imaging Clin N Am 12 (2004) Fig. 3. (A) Coronal VIBE Fat Sat pre, (B) coronal HASTE, (C) coronal HASTE at different level, (D) coronal VIBE Fat Sat post, (E) axial T1 in phase, (F) axial HASTE Fat Sat, and (G) axial VIBE Fat Sat post show multiple septae involving a cyst in the right kidney upper pole. The septae are smooth and show no enhancement post contrast injection. ADPKD is a slow progressive disease, requiring renal replacement therapy in 45% of patients by 60 years of age [16,21]. There is high inter- and intraindividual variability in progression to endstage renal disease. Despite much progress in the understanding of the molecular basis of ADPKD, the severity and progression of ADPKD in an individual remains unpredictable and the mechanism of renal failure is understood poorly. In addition to gene type, other risk factors are associated with progression to end-stage renal disease. In particular, increased renal size or renal volume is associated with a poorer renal outcome [22]. Other risk factors include early age of diagnosis, such as diagnosis in utero or in the first year of life [23], and early onset of hypertension. Once renal insufficiency develops in ADPKD, a rapid decline in renal function leading to endstage renal disease ensues. To maximize the benefits of the treatment, it is crucial to identify the patients who are at a high risk for progression to end-stage renal disease but are still early in the course of their disease with a good renal function. Recently, Washington University in St. Louis, Missouri formed the Data Coordinating Center for Polycystic Kidney Disease Studies consortium to investigate the structure-functional relationship in the disease progression of polycystic kidney disease. In this study, the volumes of the kidney, renal cyst, and hepatic cyst are quantified by MR imaging and are compared with the renal function and clinical data [2 4]. Autosomal recessive polycystic kidney disease Autosomal recessive polycystic kidney disease (ARPKD) is a hereditary disease transmitted by

6 454 F.M. EL-Merhi, K.T. Bae / Magn Reson Imaging Clin N Am 12 (2004) Fig. 3 (continued) autosomal recessive inheritance. It is characterized by dilation of renal collecting tubules and varying degrees of portal hepatic fibrosis [24]. It is divided into four subtypes depending on the age of onset: antenatal, neonatal, infantile, and juvenile. The earlier the onset of disease, the more severe the renal findings and the less pronounced the periportal fibrosis. The neonatal subtype is the most common and can be diagnosed by sonography as early as 17 weeks of gestational age. The ultrasound shows bilateral enlarged and hyperechoic kidneys. The echogenicity is attributed to the unresolved 1- to 2-mm cystic dilatation of the collecting tubules that increases the number of acoustic interfaces [25]. These neonates succumb to pulmonary insufficiency in the first few days of life [26]. The role of MR imaging in pregnant women for the evaluation of fetuses has been increasing, especially in fetuses with equivocal second-trimester ultrasound. On MR imaging, fetuses with ARPKD have enlarged bilateral kidneys with high signal intensity on T2-weighted images attributed to the innumerable irresolvable small cysts (Fig. 8). In older children, the liver may show bile-duct dilation and evidence of portal hypertension and varices. Tuberous sclerosis Tuberous sclerosis (Bourneville disease) is a hereditary phakomatosis transmitted by autosomal dominant trait. It is characterized by hamartomas involving multiple organs including kidneys, brain, skin, and heart. In the kidneys, angiomyolipomas are common. These lesions are often bilateral and multiple and tend to increase in size over time or to bleed into the subcapsular and perinephric regions [27 29]. On MR imaging, the presence of fat confirms the diagnosis of angiomyolipoma (Fig. 9), but fat-deficient angiomyolipoma may be difficult to differentiate from renal-cell carcinoma (Fig. 10). In addition, renal involvement may manifest as bilateral multiple simple cysts of various sizes involving the cortex and medulla in 15% of cases (Fig. 11) [30,31]. Renal cysts may be the earliest and only manifestation of this disorder in infancy [33] and sometimes can be

7 F.M. EL-Merhi, K.T. Bae / Magn Reson Imaging Clin N Am 12 (2004) Fig. 4. (A) Axial VIBE Fat Sat pre, (B) axial HASTE, and (C) axial VIBE Fat Sat post show a patient with ADPKD with innumerable noncomplicated cysts affecting kidneys and liver. The noncomplicated cysts usually have low T1 signal, high T2 signal, and demonstrate no enhancement post contrast injection. confused with the diagnosis of ADPKD [32]. The presence of angiomyolipoma, however, may establish the diagnosis of tuberous sclerosis. The neurologic manifestations of seizures and mental retardation may be related to the presence of subependymal and subcortical tubers and the development of giant cell astrocytoma in the brain. von Hippel-Lindau disease von Hippel-Lindau disease (VHL disease) is a hereditary phakomatosis transmitted by autosomal dominant trait. It is characterized by diverse manifestations involving multiple organs including hemangioblastoma of the central nervous system and retina, endolymphatic sac tumor, renal cyst and renal-cell carcinoma, pancreatic cyst and tumor, pheochromocytoma, and epididymal cystadenoma. Renal cyst is the most common visceral manifestation [34] occurring in 75% of patients, and involves predominantly the cortex. Renal-cell carcinoma occurs in 20% to 45% of patients and is usually multiple and bilateral (Fig. 12). Evidence from quantitative DNA analysis suggests that some renal cysts associated with VHL disease have malignant potential [35,36], which was supported by studies based on serial CT scan follow-up in patients with VHL disease [37,38]. Pancreatic presentation includes simple cysts (Fig. 13), microcystic serous cystadenocarcinoma, or islet-cell tumor. Acquired cystic renal disease Acquired cystic renal disease occurs commonly in patients treated with dialysis, but may occur in patients with chronic renal insufficiency without history of dialysis. Although the pathogenesis of cyst development is not understood fully, the duration of renal dialysis is related strongly to its occurrence. Approximately 44% to 50% of patients on long-term hemodialysis and even on peritoneal dialysis acquire renal cysts [39 41]. The

8 456 F.M. EL-Merhi, K.T. Bae / Magn Reson Imaging Clin N Am 12 (2004) Fig. 5. (A) Axial T1 in phase, (B) axial HASTE, and (C) axial VIBE Fat Sat post. Patient with ADPKD demonstrates bilateral noncomplicated and hemorrhagic renal cysts. The hemorrhagic cysts (arrows) demonstrate high T1 signal, low T2 signal, and no enhancement post contrast injection. Fig. 6. (A) Coronal VIBE Fat Sat pre and (B) coronal HASTE. Patient with ADPKD demonstrates extensive innumerable cysts, some of which are hemorrhagic, throughout the liver and kidneys. The largest of the hemorrhagic cysts (arrow) is located in the anterior segment of the right lobe of the liver.

9 F.M. EL-Merhi, K.T. Bae / Magn Reson Imaging Clin N Am 12 (2004) Fig. 7. (A) Axial VIBE Fat Sat pre, (B) axial HASTE, and (C) axial VIBE Fat Sat post show a patient with ADPKD with extensive cysts involving both kidneys and, to a lesser extent, the liver. One cyst involves the body of the pancreas. prevalence of renal cysts reaches over 90% after 5 to 10 years of dialysis. Renal cysts in acquired cystic renal disease predominately arise in the superficial aspect of the renal cortex and tend not to expand the kidneys (Fig. 14). The affected kidneys are usually atrophic at the time of cyst development. The cysts often are lined with hyperplastic and dysplastic epithelium, probably secondary to epithelial hyperplasia [42]. Patients are usually asymptomatic, but may present with flank pain or more serious complication, such as retroperitoneal hemorrhage or renal neoplasm [40 42]. Acquired cystic renal disease is associated with increased incidence of renal-cell carcinoma (approximately 7%) that may be bilateral and multiple [43 45]. Medullary sponge kidney Medullary sponge kidney is a nonhereditary disorder seen predominately in adults and rarely in children. It is characterized by cystic dilatation of the collecting ducts of the medullary pyramids [46]. The cysts can reach 8 to 10 mm in size. Medullary sponge kidney is usually bilateral and rarely unilateral or segmental [47]. The dilated ducts contain calcified deposits; approximately 50% contain nephrolithiasis. Patients may present with calculi, obstruction, infection, and hematuria. On excretory urography, the appearance varies from fine linear striations to small, round contrast collection that may contain filling defects reflecting calculi deposits [48]. A similar appearance can be seen on the interstitial phase of the postcontrast dynamic MR images [14]. Multicystic dysplastic kidney Muticystic dysplastic kidney is a nonhereditary, developmental disorder characterized by multiple renal cysts replacing functional renal parenchyma in the affected whole or segmental kidney. This abnormality is thought to be caused by complete obstruction of the ureters during nephrogenesis. Muticystic dysplastic kidney is usually diagnosed in utero or at birth. If the affected kidney is

10 458 F.M. EL-Merhi, K.T. Bae / Magn Reson Imaging Clin N Am 12 (2004) Fig. 8. (A) Axial HASTE and (B) coronal HASTE T2 images show oligohydramnios and a fetus in a breech position who has bilateral pulmonary hypoplasia and bilateral enlarged kidneys. High T2 signal intensity in the kidneys reflects innumerable small renal cysts in this fetus with ARPKD. (Courtesy of V. Narra, MD, Mallinckrodt Institute of Radiology, St. Louis, MO.) Fig. 9. (A) Axial T1 in phase, (B) axial T1 out of phase, (C) axial VIBE Fat Sat pre, and (D) axial VIBE Fat Sat post. Patient with tuberous sclerosis demonstrates bilateral multiple angiomyolipomas that maintain high signal on T1 inphase and out-of-phase sequences, but drop in signal on the VIBE Fat Sat sequence. Mild heterogeneous enhancement is identified on the post contrast injection.

11 F.M. EL-Merhi, K.T. Bae / Magn Reson Imaging Clin N Am 12 (2004) unilateral (80% 90% of cases) and missed on fetal ultrasound, it may be undetected into adulthood until it is discovered incidentally as a nubbin of calcified tissue with an atretic ureter [33,49,50]. It is associated with ipsilateral renal anomalies such as vesicoureteral reflux (25%) and with contralateral renal anomalies (40%), of which ureteropelvic junction obstruction is the most common. On fetal MR imaging, large multiple or septated renal cysts without detectable renal parenchyma are seen in the affected kidney. Parapelvic renal cyst Parapelvic renal cyst is a benign extraparenchymal cyst located in the renal sinus between the renal capsule and the cortex or between the renal capsule and the perinephric fat. It also is known as parapelvic lymphangectasia, parapelvic lymphatic, and perinephric pseudocyst [47]. Parapelvic cysts often are discovered incidentally in the elderly or seen in transplanted kidneys secondary to lymphatic obstruction. They may be seen after trauma, urinary obstruction, or surgical procedures that damage the renal pelvis, calyx, or capsule. Parapelvic cysts do not communicate with collecting system and are frequently multiple and bilateral. MR imaging demonstrates multiple renal cysts within the renal sinus that may mimic hydronephrosis (Fig. 15). Postcontrast delayed images can help differentiate unenhanced parapelvic cysts from a contrast-enhanced dilated pelvocalyceal system. The signal intensity of the contrast-enhanced collecting system varies depending on the delayed phases and on the concentration of gadolinium contrast excreted into the collecting system. Fig. 10. (A) T1 GRE, (B) T1 GRE Fat Sat, (C) T1 in phase, (D) T1 out of phase, (E) T2 IR, (F) VIBE Fat Sat pre and (G) VIBE Fat Sat post. A patient with tuberous sclerosis shows a left kidney midzone posterior aspect exophytic lesion that maintains an isointense signal to the renal parenchyma on T1 and T2 images and demonstrates no drop in signal on either out-of-phase or Fat Sat sequences. In addition, it shows an avid enhancement on the immediate postcontrast images. Initially, this was read as suspicious for renal-cell carcinoma, but the surgical pathology came back as an epitheloid angiomyolipoma. (Courtesy of C. Menias, MD, Mallinckrodt Institute of Radiology, St. Louis, MO.)

12 460 F.M. EL-Merhi, K.T. Bae / Magn Reson Imaging Clin N Am 12 (2004) Fig. 10 (continued)

13 F.M. EL-Merhi, K.T. Bae / Magn Reson Imaging Clin N Am 12 (2004) Fig. 11. (A) Coronal VIBE Fat Sat pre, (B) coronal HASTE, and (C) coronal VIBE Fat Sat post show bilateral, noncomplicated renal cysts in the same patient as in Fig. 10.

14 462 F.M. EL-Merhi, K.T. Bae / Magn Reson Imaging Clin N Am 12 (2004) Fig. 12. (A) Axial T1 in phase, (B) axial HASTE Fat Sat, and (C) axial VIBE Fat Sat post arterial phase. This patient with VHL disease status postbilateral partial nephrectomies demonstrates bilateral renal and pancreatic noncomplicated cysts and a renal-cell carcinoma (arrow) in the anterior aspect of the right kidney.

15 F.M. EL-Merhi, K.T. Bae / Magn Reson Imaging Clin N Am 12 (2004) Fig. 13. (A) Axial T1 in phase, (B) axial HASTE, and (C) axial VIBE Fat Sat post show numerous cysts replacing the pancreatic parenchyma with no enhancing foci post contrast injection identified in a patient with VHL disease. Calyceal diverticulum Calyceal diverticulum is a developmental or acquired cystic dilatation that arises from the calyx and extends into the adjacent parenchyma [48]. It also is called pyelogenic cyst. Calyceal diverticulum usually is found incidentally, but may present with calculi, hematuria, flank pain, or infection. On T2-weighted or pre- and postcontrast T1-weighted MR images, calyceal diverticulum shows the signal intensity similar to that of urine [14] (Fig. 16). Fig. 14. (A) Coronal HASTE and (B) coronal SPGE Fat Sat post in patient on chronic hemodialysis show bilateral atrophic kidneys and bilateral, acquired, noncomplicated simple cysts.

16 464 F.M. EL-Merhi, K.T. Bae / Magn Reson Imaging Clin N Am 12 (2004) Fig. 15. (A) Axial T1 SE, (B) axial T2 fast spin echo, (C) axial GRE Fat Sat pre, and (D) axial GRE Fat Sat post demonstrate left kidney multiple parapelvic cysts with no enhancement post contrast injection.

17 F.M. EL-Merhi, K.T. Bae / Magn Reson Imaging Clin N Am 12 (2004) Fig. 16. (A) Coronal true fast imaging with steady-state precession (FISP), (B) coronal HASTE Fat Sat, (C) coronal 3D fast low angle shot (FLASH) post, (D) axial true FISP, and (E) axial HASTE Fat Sat show right kidney multiple calyceal diverticulum.

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