Notes - O.13 Abnormal Fetal GU Tract.pdf

ULTR-3014 OBGYN Sonography 3 Module O.13: Abnormal Fetal GU Tract Notes Ultrasound Evaluation ABNORMAL FETAL GENITOURINARY TRACT Module O.13 April 20, 2022 Prepared for RRC Polytech Diagnostic Medical Sonography ULTR-3014 OBGYN Sonography 3 Module O.13: Abnormal Fetal GU Tract Notes TABLE OF CO...

ULTR-3014 OBGYN Sonography 3 Module O.13: Abnormal Fetal GU Tract Notes Ultrasound Evaluation ABNORMAL FETAL GENITOURINARY TRACT Module O.13 April 20, 2022 Prepared for RRC Polytech Diagnostic Medical Sonography ULTR-3014 OBGYN Sonography 3 Module O.13: Abnormal Fetal GU Tract Notes TABLE OF CONTENTS OBJECTIVES - ......................................................................................................... 3 ULTRASOUND EVALUATION ABNORMAL FETAL GU TRACT ................................. 6 Urinary Tract Abnormalities .................................................................................... 6 Introduction......................................................................................................... 6 Bladder Abnormalities ....................................................................................... 7 Nonvisualization ............................................................................................ 7 Megacystis ..................................................................................................... 8 Kidney Abnormalities ......................................................................................... 9 Bilateral Renal Agenesis .............................................................................. 9 Unilateral Renal Agenesis .......................................................................... 10 Renal Ectopia .............................................................................................. 10 Horseshoe Kidneys ..................................................................................... 10 Hydronephrosis ........................................................................................... 10 Mild Pyelectasis ..................................................................................... 10 Ureteropelvic Junction Obstruction ..................................................... 11 Ureterovesical Junction Obstruction ................................................... 12 Posterior Urethral Valves ...................................................................... 12 Urethral Atresia ...................................................................................... 13 Prune Belly Syndrome ........................................................................... 13 Complications of Urinary Tract Obstruction ....................................... 13 Renal Cystic Disease .................................................................................. 14 Multicystic Dysplastic Kidney............................................................... 14 Cystic Renal Dysplasia .......................................................................... 14 Infantile Polycystic Kidney Disease ..................................................... 15 Adult Polycystic Kidney Disease.......................................................... 15 Renal Neoplasms ........................................................................................ 16 ULTR-3014 OBGYN Sonography 3 Module O.13: Abnormal Fetal GU Tract Notes OBJECTIVES Abnormal GU Tract 1. Fetal reproductive tract anomalies: (a) hydrocele: (i) define (ii) explain clinical significance (iii) describe sonographic features (iv) identify on appropriate fetal sonograms (b) hypospadias: (i) define (ii) explain clinical significance (iii) describe sonographic features (iv) identify on appropriate fetal sonograms 2. Fetal bladder anomalies: (a) name most common reasons for non visualization (b) megacystis: (i) define (ii) explain clinical significance (iii) name most common causes (iv) describe sonographic features (v) identify on appropriate fetal sonograms (c) bladder/cloacal extrophy (i) define (ii) clinical signifigance (iii) name most common causes (iv) describe sonographic features (v) identify on appropriate fetal sonograms 3. Sonographic diagnosis of fetal renal anomalies: (a) bilateral fetal renal agenesis: (i) describe associated syndrome (ii) describe clinical significance (iii) describe main sonographic features (iv) identify on appropriate fetal sonograms (b) unilateral fetal renal agenesis: (i) describe associated syndrome (ii) describe clinical significance (iii) describe main sonographic features (iv) identify on appropriate fetal sonograms (c) hydronephrosis: (i) define ULTR-3014 OBGYN Sonography 3 Module O.13: Abnormal Fetal GU Tract Notes (ii) (iii) (iv) (v) (vi) (c) (d) (e) (f) (g) (h) describe clinical significance name most common causes define pyelectasis and hydronephrosis define caliectasis describe main sonographic features of pyelectasis, hydronephrosis and caliectasis (vii) identify on appropriate fetal sonograms (viii) describe typical sonographic features of ureteropelvic junction obstruction (ix) describe typical sonographic features of ureterovesical junction obstruction hydroureter: (i) define (ii) list the most common causes (iii) identify on appropriate sonograms (iv) describe key distinguishing features between hydroureter and dilated loops of small bowel urethral atresia: (i) define (ii) describe clinical significance (iii) associate with bladder outlet obstruction (iv) describe main sonographic features posterior urethral valves: (i) define (ii) describe clinical significance (iii) associate with bladder outlet obstruction (iv) describe main sonographic features (v) associate with the sonographic “keyhole” sign (vi) identify on appropriate sonograms (vii) describe the sonographic features prune belly syndrome multicystic dysplastic kidney: (i) describe clinical significance (ii) describe distinguishing sonographic features with hydronephrosis (iii) describe main sonographic features (iv) identify on appropriate fetal sonograms describe causes and sonographic features of cystic renal dysplasia autosomal recessive polycystic kidney disease (ARPKD): (i) describe clinical significance (ii) describe risk of recurrence (iii) describe main sonographic features (iv) identify on appropriate fetal sonograms ULTR-3014 OBGYN Sonography 3 Module O.13: Abnormal Fetal GU Tract Notes (i) autosomal dominant polycystic kidney disease (ADPKD): (i) describe clinical significance (ii) describe risk of recurrence (iii) describe main sonographic features (iv) identify on appropriate fetal sonograms (j) name most common fetal renal neoplasm (k) describe complications associated with fetal urinary tract obstruction and identify on sonograms (l) explain the purpose of fetal vesicoamniotic shunting and identify on sonograms (m) review renal association of VACTERAL Syndrome, review other associated anomalies ULTR-3014 OBGYN Sonography 3 Module O.13: Abnormal Fetal GU Tract Notes ULTRASOUND EVALUATION ABNORMAL GU TRACT Urinary Tract Abnormalities Introduction - The urinary tract is one of the most frequent sites of congenital anomalies detected with fetal sonography. A systematic approach begins with the assessment of amniotic fluid volume, identification of the urinary bladder and kidneys, localization and characterization of the abnormalities seen, and the search for associated abnormalities in other organs. Important questions to ask when considering fetal urinary tract anomalies are: A) Is the amniotic fluid volume normal? Studies have shown that fetal kidneys begin to produce urine at about 10 weeks of gestation and that fetal urine becomes the primary source of amniotic fluid volume (AFV) after about 16 weeks of gestation. A significant decrease in fetal urine output after 16 weeks of gestation results in oligohydramnios, which is a key sign of fetal GU tract anomaly. As previously discussed, serious unilateral renal anomalies are usually associated with normal AFV whereas bilateral anomalies that compromise the production of urine or the passage of urine into the amniotic fluid are associated with various degrees of oligohydramnios depending on gestational age and the severity of the problem. B) Is the fetal bladder seen in its normal location? As previously discussed, nonvisualization of the bladder is usually due to serious bilateral renal anomalies, and far less commonly, intrinsic bladder or cloacal defects, or severe IUGR. C) Does the fetal bladder appear to be abnormally big or thick-walled? A dilated or thick-walled bladder is usually a sign of bladder outlet obstruction and is most commonly associated with posterior urethral valves. D) Are both fetal kidneys seen in their normal location? A fetal kidney may not be visualized in the renal fossa because of unilateral renal agenesis, hypoplasia, ectopia, or unfavourable technical parameters. The prenatal sonographic diagnosis of these anomalies is generally difficult since the fetal bladder and AFV are normal and careful scrutiny of the fetal abdomen may not be undertaken. ULTR-3014 OBGYN Sonography 3 Module O.13: Abnormal Fetal GU Tract Notes E) Do the kidneys appear to be normal in size and echogenicity? Kidneys that appear to be too small or large should be measured and assessed against normal values for gestational age. Normal renal echogenicity increases with gestational age however kidneys are generally less echogenic than the liver. A small echogenic kidney is most commonly associated with renal dysplasia. Bilateral enlarged echogenic kidneys is most commonly associated with infantile polycystic disease. F) Is the renal collecting system (calyces, renal pelvis, or ureter) visualized? The normal renal collecting system is not visualized except for a small amount of renal pelvic dilatation (pyelectasis) in a minority of fetuses. Dilatation and visualization of the collecting system is usually due to obstructive pathologies, with ureteropelvic junction obstruction being the most common cause. Ultrasound is generally unable to distinguish obstructive and nonobstructive causes of hydronephrosis or hydroureter. G) If the kidneys appear cystic, do the cysts communicate? The most common form of macrocystic renal disease detected in utero is multicystic dysplastic kidney (MCDK) which can usually be distinguished from hydronephrosis. With hydronephrosis, the dilated renal pelvis communicates with the dilated calyces (perceived as a pattern of multiple renal cysts); in contrast, with MCDK, the multiple renal cysts do not communicate, and are also more randomly organized and vary significantly in diameter. H) Is there evidence of unilateral or bilateral abnormalities? Unilateral abnormalities should be associated with normal AFV; in contrast, bilateral abnormalities are generally associated with oligohydramnios. Bladder Abnormalities Nonvisualization - of the fetal bladder is most frequently due to specific fetal renal abnormalities(refer to the table next page). Note that all causes of renal abnormalities associated with nonvisualization of the bladder must be bilateral. Isolated, unilateral renal agenesis, ureteral pelvic junction obstruction (UPJ), and multicystic dysplastic kidney (MCDK) are associated with normal visualization of the bladder and normal AFV. UPJ and MCDK are most frequently unilateral abnormalities however there is often a co-existing abnormality in the contralateral kidney (e.g. UPJ in one kidney and agenesis of the other kidney). Infantile (and adult) polycystic kidney disease (IPKD) is always bilateral however the severity of the disease varies and the fetal bladder and AFV may appear abnormal or unremarkable (in the majority of cases, there is severe oligohydramnios and the bladder is not visualized or tiny). ULTR-3014 OBGYN Sonography 3 Module O.13: Abnormal Fetal GU Tract Notes Rarely, nonvisualization of the bladder is due to a severe bladder or cloacal abnormality or may be related to severe intrauterine growth retardation with poor renal function. The bladder forms during early embryology from the cloaca which also gives rise to the rectum and anus; maldevelopment of the cloaca leads to various bladder, uterine and rectal abnormalities. NONVISUALIZATION OF THE FETAL BLADDER Renal Abnormality Bilateral renal agenesis (Potter’s syndrome) Bilateral ureteral pelvic junction obstruction Bilateral multicystic dysplastic kidney Bilateral combinations of any of the above Infantile polycystic kidney disease Bladder Abnormality Bladder exstrophy Cloacal exstrophy Persistent cloaca Other Severe intrauterine growth retardation Megacystis - Normal fetal bladder volume varies considerably in fetuses of the same gestational age and the mean bladder volume increases with gestational age. An abnormally large fetal bladder (megacystis) is a sign of bladder outlet obstruction and should be critically evaluated, especially in association with oligohydramnios and if there is evidence of obstructive uropathy e.g. hydroureters and/or hydronephrosis. The most common cause of megacystis is posterior urethral valves. Other causes include urethral atresia or stricture, prune belly syndrome, primary megacystis (megacystis-megaureter syndrome), megacystis-microcolon-intestinal hypoperistalsis syndrome (MMIHS), and cloacal malformations. ULTR-3014 OBGYN Sonography 3 Module O.13: Abnormal Fetal GU Tract Notes Kidney Abnormalities Bilateral Renal Agenesis (BRA) - or Potter syndrome, is a lethal abnormality characterized by congenital absence of both kidneys and severe oligohydramnios. The reported incidence of BRA is about 1 in 4,000 births. Neonatal mortality is attributable to severe pulmonary hypoplasia due to severe oligohydramnios. Associated anomalies are relatively common, especially musculoskeletal (most notably sirenomelia), and cardiovascular. The key sonographic features of BRA include severe oligohydramnios and nonvisualization of the fetal kidneys and fetal bladder. Before 16 weeks gestation, AFV is not dependent on fetal renal function and fetal urine output and may be normal despite absence of the fetal kidneys. The inability to visualize fetal kidneys is the most specific finding of BRA however kidneys may difficult to visualize because of poor image quality associated with severe oligohydramnios or maternal obesity. Common pitfalls include bowel or adrenal glands in the renal fossae that are mistaken for kidneys. Recognition of the distinctive, flattened appearance of the adrenal gland on sagittal images of the fetal abdomen, referred to as the Alying down adrenal sign@, may be helpful to confirm the fetal kidney did not develop in the renal fossa,. Consistent nonvisualization of the fetal bladder over a one hour period in the presence of severe oligohydramnios is a reliable secondary sign of BRA; conversely, visualization of a normal fetal bladder excludes the diagnosis. Several techniques have been described and proposed to improve visualization of the fetus in the presence of oligohydramnios including intra-amniotic and fetal intraperitoneal infusion of isotonic saline, endovaginal sonography (EVS), and colour Doppler (CD) assessment of the fetal aorta and renal arteries. Saline infusion appears to be used sparingly; EVS may be most helpful between 14 and 18 weeks gestation and in breech fetuses; CD may be used to successfully diagnose absent renal arteries and indicate the diagnosis of BRA however it is most helpful to rule out the diagnosis by visualization of the renal arteries. Other frequent, nonspecific, sonographic findings seen with BRA include dolicocephaly (manifests as a low cephalic index) and pulmonary hypoplasia (manifests as a small chest size or a decreased chest circumference to abdominal circumference ratio. ULTR-3014 OBGYN Sonography 3 Module O.13: Abnormal Fetal GU Tract Notes Unilateral Renal Agenesis - The reported incidence of unilateral renal agenesis (URA) is about 1 in 1,1000 births, which is four times more common than BRA. URA is associated with normal AFV, normal visualization of the fetal bladder, and a good prognosis. Fetal sonographic diagnosis is uncommon, presumably because AFV and the fetal bladder appear normal and the absent kidney is overlooked when the renal fossae is evaluated. Renal Ectopia - The reported incidence of renal ectopia (RE) varies between 1 in 500 and 1 in 1,200 births. The most common form of renal ectopia is pelvic kidney. A pelvic kidney may be diagnosed if a kidney is missing in the renal fossa and a reniform structure is seen in the pelvis adjacent to the bladder or iliac wing however prenatal sonographic diagnosis is very uncommon for the same reasons attributable to URA. Horseshoe Kidneys - The reported incidence of horseshoe kidneys (HK) is about 1 in 500 births. The fetal diagnosis may be made if a connecting bridge of renal tissue is shown however most cases are missed in the fetus for the same reasons attributable to URA and RE. Hydronephrosis - is the most common fetal GU tract abnormality detected with prenatal sonography. Fetal hydronephrosis is usually due to obstructive lesions, with ureteropelvic junction (UPJ) obstruction representing the most common cause. The most common cause of nonobstructive hydronephrosis is vesicoureteral reflux (VUR). It is usually not possible with prenatal ultrasonography alone to distinguish between obstructive and nonobstructive causes of fetal hydronephrosis. Mild Pyelectasis - represents mild dilatation of the renal pelvis. It is a relatively common sonographic finding which may be seen in normal fetuses as a transient, physiologic phenomenon or it may be pathologic and represent the earliest manifestation of a urinary tract abnormality which requires further surveillance. In addition mild fetal renal pyelectasis before 21 weeks gestation is associated with an increased risk of aneuploidy, especially trisomy 21 or Down syndrome; in one series, the frequency of chromosomal abnormalities was 1.1% in fetuses with isolated pyelectasis, The technique for measuring the degree of renal pyelectasis is based on an anteroposterior diameter measurement of the fluid-dilated renal pelvis (RPD) in an appropriate axial scan of the mid portion of the fetal kidney. Several authors have published studies regarding mild fetal pyelectasis with different reporting thresholds for what constitutes a significant finding requiring further fetal surveillance and postnatal evaluation with the possibility of corrective surgery. The appropriate threshold for initiating further ULTR-3014 OBGYN Sonography 3 Module O.13: Abnormal Fetal GU Tract Notes investigation of mild fetal pyelectasis remains controversial. Variables include gestational age and the degree of maternal hydration has also been shown to influence the degree of fetal pyelectasis which may increase the number of false-positive diagnoses of potentially pathologic pyelectasis. . In general, prior to 20 weeks gestation, RPD should measure less than 4 mm and measurements greater than 4 mm are considered abnormal and warrant further ultrasound evaluation. Values between 5 and 10 mm after 20 weeks gestation are generally reported as significant finding which requires follow up however not all investigators agree. Investigators agree that measurements greater 10 mm should be the subject of detailed postnatal assessment. Other criteria proposed for the reporting of clinically significant hydronephrosis include the presence of caliectasis with pyelectasis and a ratio of the anteroposterior diameters of the renal pelvis and kidney greater than 50%. To date, fetal renal Doppler has not proven to be significantly helpful in the diagnosis of fetal hydronephrosis. On serial studies, RPD may increase, decrease, or remain the same. An increase in RPD increases the likelihood that postnatal corrective surgery may be required. If RPD persists on serial ultrasound studies 6 to 8 weeks apart, postnatal follow-up studies are warranted. Ureteropelvic Junction Obstruction Ureteropelvic junction (UPJ) obstruction is the most common cause of neonatal hydronephrosis. UPJ obstruction is most often unilateral with only 10% to 30% of cases being bilateral. Most cases of UPJ obstruction are caused by a muscular abnormality in ureteral wall (classified as functional) rather than the result of ananatomic lesion such as an aberrant vessel or a kink. The sonographic findings of unilateral UPJ include dilatation of the renal pelvis with or without dilatation of the calyces. The ureter, bladder, and amniotic fluid volume should appear normal (in some cases, there may be mild polyhydramnios). Bilateral UPJ obstruction is associated with variable degrees of oligohydramnios and a variable prognosis depending on the severity and duration of renal obstruction. Ureterovesical Junction Obstruction - UVJ obstruction is the second most ULTR-3014 OBGYN Sonography 3 Module O.13: Abnormal Fetal GU Tract Notes common cause of fetal and neonatal hydronephrosis. UVJ obstruction may be due to a number of causes, which may be classified as primary or secondary. Bilateral UVJ obstruction is uncommon. The sonographic findings of unilateral UVJ include variable degrees of ureteral dilatation (hydroureter) and variable degrees of hydronephrosis. The bladder and amniotic fluid volume should appear normal. With bilateral UVJ obstruction, there is variable severity of oligohydramnios and depending on the severity and duration of the urinary obstruction. Se figure 129. A secondary cause of UVJ obstruction with a specific sonographic appearance is ureterocele. A ureterocele is prolapse of the distal ureteric mucosa into the urinary bladder causing a cystic dilatation of the prolapsed segment in the bladder. It is called simple ureterocele if the ureter is normally located in the bladder wall and ectopic ureterocele if the ureter inserts in the bladder in an ectopic location. An ectopic ureterocele is associated with renal duplication (duplex kidney). Ectopic ureterocele is usually associated with focal or segmental hydronephrosis involving the upper moiety or pole of the duplex kidney. The diagnosis of a ureterocele may be made when a thin-walled cystic structure can be seen in the bladder in association with hydroureter and/or hydronephrosis. A dilated ureter (hydroureter) should be differentiated from fluid-dilated loops of bowel (bowel obstruction) since both appear as fluid-filled tubular structures in the fetal abdomen. A hydroureter is located posteriorly and should be seen to communicate with the renal pelvis and/or bladder; although tortuous, the long axis of a hydroureter is craniocaudal. Obstructed fluid-filled loops of bowel are more anterior and more randomly oriented than hydroureter, and may contain intraluminal particles; the kidneys and bladder should appear normal. Peristalsis may be seen with both hydroureter and dilated bowel loops although it is more prominent with bowel. Posterior Urethral Valves - The most common cause for urinary obstruction at the urethral level is posterior urethral valves (PUV), which is valve like tissue flaps in the proximal or prostatic portion of the male urethra. PUV may cause either total, intermittent, or partial obstruction, resulting in variable sonographic findings and prognosis. The most ULTR-3014 OBGYN Sonography 3 Module O.13: Abnormal Fetal GU Tract Notes specific sonographic finding is the Akeyhole sign@ which describes a dilated urinary bladder with a dilated proximal urethra; the bladder wall may appear abnormally thickened, and there may be bilateral hydroureters and hydronephrosis. Oligohydramnios may be mild to severe depending on the degree of obstruction. Urethral Atresia - another cause of urethral level obstruction and causes the most severe form of urinary obstruction since fetal urine is unable to pass into the amniotic fluid. Typical sonographic findings include megacystis associated with anhydramnios (no detectable amniotic fluid). Prune Belly Syndrome - PBS (aka Eagle-Barrett syndrome) is characterized by absent anterior abdominal musculature, undescended testes (cryptorchidism), and urinary tract abnormalities (megacystis, hydroureters). The pathogenesis of this syndrome is controversial however it appears to be multifactorial. It is hypothesized that early fetal urethral obstruction (due to valves or other etiology) leads to massive distention of the bladder and ureters, which in turn causes pressure atrophy of the abdominal wall muscles. Bladder distention also interferes with the descent of the testes and is responsible for cryptorchidism. The prognosis for prune-belly syndrome is variable and depends on the severity of the obstruction and the degree of oligohydramnios. With severe urethral obstruction, oligohydramnios is severe and the infant is at risk for neonatal respiratory distress secondary to pulmonary hypoplasia. Complications of Urinary Tract Obstruction - Pressure buildup in the urinary tract may cause rupture of the urinary tract and urine to collect in the abdomen. Rupture may occur in the kidney, ureter, or bladder depending on the cause and level of obstruction. Fetal ascites due to urinary tract rupture is known as urinary ascites. Rupture of the kidney may result in urinary ascites or a localized, perinephric collection of urine referred to as a perinephric urinoma or pseudocyst. Intra-abdominal calcification may also be associated with urinary tract rupture and appears as echogenic foci in the fetal abdomen or in the wall of a urinoma. Fetal urinary tract rupture and urinary ascites should be suspected if you see fetal ascites associated with oligohydramnios and intra-abdominal calcification. An interventional procedure which may be helpful in the management of fetal urethral level obstruction is vesicoamniotic shunting (VAS). With VAS, a drainage tube is placed in the fetal bladder under ultrasound guidance and drains permanently into the amniotic fluid. The objective of VAS is to relieve back pressure on the urinary tract and prevent or minimize renal damage (dysplasia), correct oligohydramnios, and prevent or minimize pulmonary hypoplasia. The selection criteria for VAS is controversial and will not be considered at this time. ULTR-3014 OBGYN Sonography 3 Module O.13: Abnormal Fetal GU Tract Notes Renal Cystic Disease - Renal cystic diseases manifesting in the fetus are multicystic dysplastic kidney (MCDK), cystic renal dysplasia (CRD), autosomal recessive polycystic kidney disease (ARPKD), autosomal dominant polycystic kidney disease (ADPKD). A wide variety of rare inherited syndromes, genetic and chromosomal disorders are associated with cystic kidneys. Renal cystic disease may be associated with aneuploidy with the most common chromosome abnormality being trisomy 13 (approximately 30% of trisomy 13 fetuses are reported to have a cystic renal abnormality). Multicystic Dysplastic Kidney - MCDK is also referred to as Potter Type II renal cystic disease. MCDK results from very early and severe urinary tract obstruction. With the most severe form of MCDK, the entire kidney is replaced with multiple cysts of varying size and there is no appreciable amount of normal renal tissue present (making the kidney totally functionless). MCDK is not genetically transmitted and is not associated with disease in other organs such as the liver or pancreas. MCDK is usually unilateral (70% to 80% of cases) however in as many as 40% of cases there is a contralateral renal anomaly (UPJ obstruction, bilateral MCDK, renal agenesis, or renal hypoplasia). MCDK appears as a cystic kidney with multiple, noncommunicating cysts of varying size and no normal parenchymal tissue-contour is distorted by cysts. The bladder and AFV should appear normal with unilateral MCDK; with a contralateral renal abnormality, the bladder may be small and there should be varying degrees of oligohydramnios. The appearance and size of MCDK may change significantly over time with cysts either increasing or decreasing in size or initially enlarging and later regressing. Partial or segmental MCKD may occur with duplex kidney. The main differential diagnosis of MCDK is severe hydronephrosis. The main distinguishing feature is the pattern of the renal cysts. With MCDK, cysts are randomly distributed, noncommunicating, and of variable size; in contrast, with hydronephrosis, the renal cysts are similar in size, communicate with each other, and are systemically organized (peripheral cysts represent calyceal dilatation and the central medial cyst represents the dilated renal pelvis. Cystic Renal Dysplasia - CRD is also referred to as Potter Type IV renal cystic disease. CRD is believed to be the consequence of severe lower urinary obstruction in the 2nd or 3rd trimester of pregnancy and is most commonly associated with posterior urethral valves (not surprisingly since this is the most common cause of lower urinary tract obstruction. The sonographic appearance of CRD is variable however the most typical finding is a small echogenic kidney with one or several small subcapsular, cortical cysts associated with evidence of urinary obstruction. Renal cysts associated with CRD may change in size over time as well as the size of the kidney and parenchymal echogenicity. Renal dysplasia may not demonstrate any cortical cysts or increased parenchymal ULTR-3014 OBGYN Sonography 3 Module O.13: Abnormal Fetal GU Tract Notes echogenicity thus the absence of renal dysplasia cannot be accurately predicted. Autosomal Recessive Polycystic Kidney Disease - ARPKD is also known as Potter Type I renal cystic disease and infantile polycystic kidney disease. ARPKD is an autosomal recessive disorder with a wide clinical spectrum. Couples who have a child with ARPKD have a 25% risk of having another affected child with each subsequent pregnancy. ARPKD involves both kidneys and the liver (hepatic fibrosis). On ultrasound, both kidneys are symmetrically enlarged (3 to 10 times larger than normal) and exhibit increased echogenicity. Distinct parenchymal cysts are usually too small to be resolved. In most cases, renal function is severely impaired, and there is severe oligohydramnios and the bladder may not be seen. The size of the kidneys and cyst size do not correlate with renal function. ARPKD may be diagnosed as early as 16 weeks on the basis of oligohydramnios and the characteristic renal changes. Because of the variability in expression and gestational age onset, the kidneys may appear normal initially and only become abnormal later on. Thus, a normal sonogram in a fetus at risk for ARPKD does not exclude the disease. In most cases, oligohydramnios and renal abnormalities are evident by 24 to 26 weeks gestation. A ratio which may be helpful in the assessment of renal size is the ratio of kidney circumference to abdominal circumference (KC/AC ratio) which is reported to be relatively constant in normal fetuses throughout the 2nd and 3rd trimester of pregnancy at 0.27 to 0.30 (27% to 30%). An elevated KC/AC ratio (40%) is an indication of renal enlargement and has been reported to be most commonly associated with ARPKD. ARPKD may be associated with another autosomal recessive disorder known as MeckelGruber syndrome. The triad of anomalies in this syndrome are IPKD, encephalocele, and polydactly. A careful fetal survey of the head and hands should be undertaken whenever ARPKD is suspected. Autosomal Dominant Polycystic Kidney Disease - ADPKD is also known as autosomal dominant polycystic kidney disease or Potter Type III renal cystic disease. ADPKD is an autosomal dominant disorder which only rarely manifests in the fetus or prior to adulthood. The disease is bilateral however the sonographic appearance in the fetus is variable. Nephromegaly with or without an increase in renal echogenicity is the most common finding; cortical cysts may or may not be seen; AFV is usually normal. ADPKD can be difficult or impossible to distinguish sonographically from ARPKD. The diagnosis of ADPKD can be made if there is a positive family history however affected parents may not be aware of their disease prior to the diagnosis in the affected child (the recurrence risk of ADPKD is 50%). Ultrasound evaluation of the parents’ kidneys should be undertaken. In adults, ADPKD manifests as enlarged kidneys with multiple parenchymal cysts of varying size. Fetal ADPKD is indicated if one parent shows evidence of ADPKD. ULTR-3014 OBGYN Sonography 3 Module O.13: Abnormal Fetal GU Tract Notes Renal Neoplasms - All congenital renal neoplasms are rare and prenatal sonographic diagnosis has been scant. The most common congenital renal tumour diagnosed in utero is mesoblastic nephroma which is a benign tumour with a good prognosis. Renal neoplasm should be suspected if a unilateral solid mass is seen arising from the kidney or renal area.