Assessment of Renal Shape of Horseshoe Kidney with Multidetector Row CT in Adult Patients: Relationship between Urolithiasis and Renal Isthmus

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1 Toki J Exp Clin Med., Vol. 38, No. 4, pp , 23 Assessment of Renl Shpe of Horseshoe Kidney with Multidetector Row CT in Adult Ptients: Reltionship etween Urolithisis nd Renl Isthmus Shuichi KAWADA *, Tmki ICHIKAWA *, Jun KOIZUMI *, Jun HASHIMOTO *, Jun ENDO *2, Kzunou HASHIDA *2, Hiroshi YAMAMURO *, Tkeshi NOMOTO *3, Yuki SAKAMOTO *4 nd Yutk IMAI * Deprtments of * Rdiology, *3 Urology, *4 Orl surgery, Toki University School of Medicine *2 Deprtments of Rdiology, Toki University Hchioji Hospitl (Received August 22, 23; Accepted Octoer, 23) Ojective: The im of this study ws to evlute the reltionship etween urolithisis nd chrcteristics of renl shpe in dult ptients with horseshoe kidney (HSK) dignosed on multidetector row computed tomogrphy (MDCT). Methods: We evluted 36 ptients with HSK nd urolithisis (Group A) nd 7 ptients with HSK without urolithisis (Group B) whose disese ws dignosed on non-contrst MDCT. Two rdiologists mesured minimum width of the renl isthmus nd mximum length of the renl pelvis nd evluted coexisting neoplstic diseses on xil computed tomogrphic (CT) imges with 5-mm reconstruction, nd we compred those mesurements etween the Groups A nd B. Results: The overll men mximum length of the renl pelvis, mm, did not differ significntly etween the 2 groups. Minimum isthmus width ws lrger in ptients with HSK nd urolithisis (. 5.6 mm), thn those without urolithisis ( mm). No ptient in either groups hd urologicl renl tumor. Conclusions: Ptients of HSK might hve tendency of high incidence of stone formtion. Becuse urolithisis is risk fctor for tumors of the renl pelvis, monitoring of ptients with HSK requires creful ttention to isthmus width on CT imges. Key words: computed tomogrphy, horseshoe kidney, isthmus, urolithisis INTRODUCTION Horseshoe kidney (HSK) is the most common fusion nomly, with incidence of one in 4 to 666 reported sed on utopsy nd rdiologic series [, 2]. HSKs re generlly linked t the lower poles y n isthmus of prenchym [, 2] nd re ssocited with wide vriety of coexisting nomlies [2-9]. Most dult ptients with HSK re symptomtic, nd the nomly is noticed incidentlly on rdiologic exmintion, such s ultrsound or computed tomogrphy (CT) [2-4]. However, ntomicl normlities, such s high insertion of the ureter or its nterior course over the isthmus, predispose the ptient to impired dringe of the collecting system, urinry stsis, nd incresed incidence of ureteropelvic junction (UPJ) ostruction nd stone formtion [, 5, 6]. Urolithisis is the most common compliction of HSK, with reported incidence of 2 to 6% [5, 9], nd is elieved to occur most commonly secondry to urinry trct infection nd stsis relted to the norml ntomy of the UPJ nd errnt ureteric course, such s high insertion into the renl pelvis [4-6, ]. HSK is difficult to dignose y sonogrphy, especilly if the isthmus is not seen, ut HSK is usully identified esily on CT []. Renl shpe including collecting system depends on isthmus width [7]. We evluted whether urolithisis ws relted to chrcteristics of renl shpe, especilly minimum width of the isthmus, of the HSK on multidetector row CT (MDCT) in dult ptients. PATIENTS AND METHODS Informed consent ws not required ecuse this ws retrospective study pproved y our institutionl review ord. Between Jnury 26 nd Decemer 22, 3 dult ptients were dignosed with HSK using MDCT. We selected 6 ptients who were performed non-contrst CT exmintions of the region etween the domen nd pelvis nd divided these ptients into 36 ptients (24 men, 2 women; ged 27 to 9 yers, men ge 64.2 ± 4.8 yers) with urolithisis (Group A) nd 7 ptients (4 men, 3 women; ged 2 to 9 yers, men ge 62.9 ± 7.3 yers) without urolithisis. Group A included 28 ptients with renl stones, 7 ptients with ureterl stones, nd 2 ptients with ldder stones; ptients with urolithisis hd oth ureter nd ldder stones. Contrst-enhnced CT ws performed in 66 ptients (Group A, 2; Group B, 45), computed tomogrphic (CT) ngiogrphy in 2 (Group A, one; Group B, ), dynmic study of the upper domen in 8 (Group A, 8; Group B, ), nd CT urogrphy in (Group A, 5; Group B, 6). MDCT w s per f ormed using 8- t o 28-row MDCT scnners of.6- to one-mm slice thickness (LightSpeed, GE, Milwukee, WI, USA; Somtom Shuichi KAWADA, Deprtment of Rdiology, Toki University School of Medicine, 43 Shimokusy, Isehr, Kngw , Jpn Tel: Fx: E-mil: kwshu@is.icc.u-toki.c.jp 59

2 Fig. The nrrowest prt of the connection etween the hlves of the kidney on xil imge ws considered the renl isthmus (rrow). Right side fusion IVC mm Midline fusion Ao Left side fusion Fig. 2 Divide fusion site of the isthmus. Isthmus: rrow, Center of the HSK: rrowhed Midline fusion: less thn 5mm on oth sides from the center of the HSK On this cse, the isthmus is divided into the left side fusion. IVC: inferior ven cv Ao: ort IVC Ao Fig. 3 Method of mesurement. Minimum width of the renl isthmus (llows). Mximum length of the renl pelvis (llowheds) IVC: inferior ven cv Ao: ort Senstion Crdic 64, Definition, Definition FLASH, Siemens, Forccheim, Germny; Aquilion, Toshi, Tokyo, Jpn). Conventionl contrst-enhnced CT exmintions were performed using 2 ml/kg of nonionic contrst mteril t rte of.5 ml/s with 2-s scnning dely. CT ngiogrphy exmintions were performed using ml of nonionic contrst mteril t rte of 4 ml/s, nd scnning dely ws determined using olus trcking method. Other prmeters of CT ngiogrphy were 2 kvp, 25 mas, nd.5-s rottion time. CT urogrphy ws performed using 3-s scnning dely. Two rdiologists ech with more thn 2 yers experience interpreting CT imges, reviewed xil MDCT imges with - to 5-mm reconstruction intervl on picture rchiving nd communiction system worksttion. The nrrowest prt of the connection etween the hlves of the kidney ws considered the renl isthmus (Fig. ). For divide fusion site the isthmus, those rdiologists mesured mximum dimeter of the outline of the HSK on the xil imge nd decided the center of the kidneys. Midline fusion ws clssified the position of the minimum width of the renl isthmus ws less thn 5mm on oth sides from the center (Fig. 2). They independently mesured minimum width of 6

3 Fig. 4 A 72-yer-old womn with the widest miniml isthmus width in Group A. (,, c) Axil computed tomogrphic imges with contrst enhncement show wide isthmus (24 mm): rrow (). These imges show left ureterovesicl junction stone: rrowhed (c), expnsion of the left renl pelvis, nd pyelonephritis (). c Tle Renl function nd renl shpe. group A group B p Minimum width of isthmus (mm). ± ± 5. P =.48 Cr. (mg/dl) [.6-.].22 ±.8.4 ±. P =.52 Renl function egfr (ml/min./.73m 2 ) [ 9] 7. ± ± 27.2 P =.4 BUN (mg/dl) [9-2] 9.9 ± ± 2.8 P =.67 Right side 9.3 ± ± 8.9 P =.53 Mximum length of pelvis (mm) Left side.7 ±. 9.3 ± 5.8 P =.57 Mx size 4.3 ± ± 8.8 P =.27 Cr.: cretinine; egfr: estimted glomerulr filtrtion rte; BUN: lood ure nitrogen; Mx size: mximum length of pelvis on oth sides the renl isthmus nd mximum length of the renl pelvis on ech side on non-contrst enhnced xil CT imge with 5-mm reconstruction in ech ptient (Fig. 3), nd we used the men vlue of ech of those mesurements y the 2 rdiologists s mesured vlue. We nlyzed the correltion etween isthmic width nd renl pelvic length y liner regression nlysis on oth groups. We recorded renl function (cretinine: Cr., estimted glomerulr filtrtion rte: egfr nd lood ure nitrogen: BUN). We compred demogrphic dt, renl function, minimum isthmus width, nd mximum renl pelvis length etween groups using chi squre test, student t-test, nd Mnn-Whitney U-test. Sttisticl significnce ws set t P <.5. Those 2 rdiologists evluted coexisting urologicl diseses excluding urolithisis nd neoplstic diseses dignosed on non-contrst or contrst enhnced CT. The two resolved ny disgreement through discussion to chieve consensus. RESULTS On ll ptients, two kidneys were connected y n isthmus t the lower poles. There ws no rre vrition of HSK with common renl pelvis. There ws of lterl fusion which one of the pelviclycel systems drined portion of renl tissue which extended cross the midline [2]. Tle shows fusion site. Ptients with midline fusion were 35 nd ptients with lterl fusion were 7, nd left side fusion ws more frequently thn right fusion on oth groups (Group A: 42, Group B: 23). The overll men minimum width of renl isthmus 6

4 Fig. 5 A 74-yer-old womn with the lrgest renl pelvis, right ureteropelvic junction ostruction (UPJO), nd pyonephrosis. () Axil nd () coronl reformtted computed tomogrphic imges with contrst enhncement show right severe hydronephrosis nd pyonephrosis cused y UPJO nd urinry trct infection. c Fig. 6 A 2-yer-old womn with neurofiromtosis type. (, ) Axil nd (c) coronl reformtted computed tomogrphic imges without contrst enhncement show severe hydronephrosis, hydroureter, nd neurogenic ldder. (, c) The ppernce of the renl pelvis opening is consistent with horseshoe kidney. ws. ± 5.3 mm; in 3 ptients, the isthmus consists of thin firous nd which ws less thn mm. Minimum width of isthmus ws lrger in Group A thn B (P =.48). And the lrgest minimum width of isthmus, 24 mm, ws in Group A (Fig. 4). Men minimum width of renl isthmus ws 8.4 ± 5.mm on midline fusion ptients nd it ws.7 ± 5.9 mm on lterl fusion ptients. There ws no significnt difference of minimum width of renl isthmus on fusion site (P =.78). The overll men mximum length of the renl pelvis ws 2.7 ± 9.2 mm, nd mximum renl pelvis 62

5 Tle 2 Frequencies of coexisting diseses. Urologicl disese without urolithisis group A group B 6.% (22/36) 45.7% (32/7) Neoplsm* 3.9% (5/36) 2.4% (5/7) Others 8.3% (3/36).4% (8/7) * Non urologicl neoplsm in oth groups Neoplsm: pncretic c. colorectl c. gstric c. prostte c. HCC, mlignnt lymphom etc. Tle 3 Coexisting urologicl nd neoplstic diseses. group A group B Urologicl disese 36 ptients 32 ptients Renl cyst Hydronephrosis Pyelonephritis Renl trophy UPJO Renl injury Renl infrction Neurogenic ldder Bldder crcinom Totl Neoplsm 5 ptient 5 ptients Pncretic cncer Colorectl cncer Gstric cncer Gll ldder cncer HCC Cervicl cncer Prostte cncer IPMN Mlignnt Lymphom Liver metstses Mlignnt peritonitis Totl 5 7 HCC: heptocellr crcinom; IPMN: intrductl pncretic mucinous neoplsm; UPJO: ureteropelvic junction ostruction. Totl numer of diseses exceeded the numer of ptients ecuse some ptients hd more thn 2 diseses length did not differ significntly etween Groups A nd B (P =.27). UPJ ostruction cused the lrgest mximum renl pelvis length (65 mm) (Fig. 5). One ptient in Group A nd one in Group B hd hydronephrosis with renl trophy. In Group A, Hydronephrosis (dilttion of mm nd more of renl pelvis) in 7 of the 2 ptients ws cused y ureterl stones. In one of those ptients with hydronephrosis nd renl trophy in Group B, the youngest ptient in oth groups, neurogenic ldder ws ssocited with neurofiromtosis type (Fig. 6); nother ptient hd left-side hydronephrosis s result of renl hilr lymph node metstsis from pncretic cncer. There ws no reltionship etween minimum isthmus width nd mximum renl pelvis on oth groups (R 2 =.4). Demogrphic dt did not differ significntly etween Groups A nd B (ge, P =.46; sex, P =.46). Tle 2 shows renl function (Cr., egfr nd BUN) nd renl shpe (minimum width of isthmus nd mximum length of renl pelvis) findings for oth groups. Overll men Cr. ws. ±.32 mg/dl, men egfr ws 68.8 ± 3.4 ml/min/.73 m 2 nd men BUN ws 8.4 ± 2.4 mg/dl. Neither Cr., egfr nor BUN did not differ significntly etween Groups A nd B (P =.52, P =.48, P =.67). The level of Cr. ws norml (<. mg/dl) in 8 ptients (8/6, 75.5 %), egfr ws norml ( 9) in 5 ptients (5/6, 4.2%) nd BUN ws norml (9 to 2 mg/dl) in 82 ptients (82/6, 77.4 %). Tle 3 shows frequencies of coexisting diseses nd coexisting urologicl diseses excluding urolithisis 63

6 Fig. 7 A 65-yer-old mn with expnsion of oth sides of renl pelvis. (, ) Axil computed tomogrphic imges with contrst enhncement show ilterl diltion of the renl pelvis (right, 23 mm; left, 24 mm) of unknown cuse. nd neoplstic diseses. There ws no renl mlignnt tumor in either groups. DISCUSSION HSK is well-known congenitl nomly of the upper urinry trct [, 2]. HSK results from the fusion of metnephric uds etween weeks 4 nd 8 of emryogenesis, which locks their cephlic migrtion nd norml rottion [, 3, 7, 9]. The inferior mesenteric rtery prevents the crnil migrtion of the isthmus of the fused kidney, which remins in the lower prt of the domen [, 7, 9]. Typiclly, the urinry collection system is nteriorly displced, with lying nterior to the isthmus [-7]. When fusion is in the midline, the position of the renl pelvis depends on the width of the isthmus [7], which comprises norml kidney tissue or firous nd. The developing kidneys re connected y n isthmus contining true renl prenchym when norml fusion results from the errnt migrtion of posterior nephrogenic cells [3].Alterntively, HSK results when medin fusion of the metnephric tissues during n erly emryologic stge produces firous isthmus [4]. In 5% of HSK, the isthmus is firous; [5] the isthmus ws firous in three of our ptients (2.8%). Moreover, the renl pelvis is often lrge, fly, nd extrrenl, nd the ureter inserts normlly high in the pelvis [, 7]. In our study, men mximum length of the renl pelvis ws 2.7 ± 9.2 mm, nd mximum renl pelvis length did not differ significntly etween ptients with HSK with or without urolithisis. Men renl pelvis length of 2.2 to 3.3 mm hs een reported nd is consistent with our results [3]. UPJ ostruction ccounted for the longest mximum renl pelvis length (65 mm) (Fig. 5), ut the cuse of ureterl stenosis ws uncler in ptient with mximum length of renl pelvis out 24 mm (Fig. 7). Therefore, we considered tht ureterl stenosis does not necessrily ccompny diltion of the renl pelvis in ptients with HSK. Glodny's group [3] offers the only report out the shpe of HSK on CT evlution. Becuse fusion occurs t the midline in out hlf of HSKs, they mesured the width of ech side from the fusion site nd reported width t the right of 6.3 mm nd t the left of 34.4 mm on xil CT imge [3].They lso evluted isthmus loction, length of the fusion site longitudinlly, nd renl rottion nd rgued ginst the rule tht rottion of the renl xis depends on whether crniocudl length of isthmus is more or less thn third of renl length [3, 2]. However, they did not ssess differences of clinicl significnce ssocited with renl shpe. More thn hlf cses hd left side fusion in our study. Becuse the isthmus is in front of the dominl ort nd dominl ort lid on the left side of the verter in mny cses, left side fusion my e occurred frequently. Mny HSKs re symptomtic nd found incidentlly. In our study, most ptients demonstrted norml renl function, nd out 69.4% of ptients with HSK with urolithisis hd no symptoms. However, wide vriety of ssocited congenitl nd cquired genitourinry nd nongenitourinry nomlies re ssocited with HSK [2-, 5-7]. High insertion of the ureter into the renl pelvis in up to 35% of cses cuses vrying degrees of stenosis of the UPJ tht my often cuse prolems [5, 6]. Stone diseses re lso common in HSK. Kidney stones develop in 2 to 6% of ptients nd re ssocited with ostruction nd recurrent infections [5]. Urinry stsis nd urolithisis lso predispose HSK to infection, which occurs in 27 to 4% of ptients, in our study, 36 of 6 dult ptients (34.%) hd urolithisis, incidence similr to tht previously reported [8]. To our knowledge, however, the reltionship etween renl shpe nd stone formtion hs not een evluted on ultrsonogrphy (US) or CT exmintion. The isthmus my not e visulized on US for severl resons []. In pproximtely 5% of fused kidneys, the firous connecting nd my not e visile on US. As well, the isthmus is usully situted low in the domen, t the level of the L4-5 verterl odies, n re frequently oscured y owel gs []. The isthmus my lso e mistken for norml ntomic structures, such s the pncres, or for pthologic 64

7 retroperitonel conditions. We speculted tht mlrottion with nterior displcement of the collecting system, nrrowing of the renl hilum, nd superior nd lterl ureteric insertion into the renl pelvis were severe in cses of HSK with wide isthmus nd tht wide isthmus ws risk fctor of stone formtion. Becuse CT is useful for the ccurte determintion of stone loction nd volume nd is used routinely prior to tretment in ptients with HSK, we evluted width of the isthmus on CT. In our study, minimum isthmus width of ptients with HSK ws lrger in those with urolithisis (. ± 5.6 mm) thn without urolithisis (9.5 ± 5. mm). As expected, these results showed tht wide isthmus ws risk fctor for stone formtion. Tretments of ptients with HSK with urolithisis include percutneous or lproscopic nephrolithotomy, extrcorporel shock wve lithotripsy, nd surgery [5, 6]. Surgicl tretments of ptients with HSK with urolithisis nd UPJ ostruction re pyeloplsty nd lproscopic or open hemi/totl nephrectomy [8]. The choice of tretment depends on stone size/loction nd the ppernce of the pelviclycel system on preopertive imging [5, 6, 8]. Prticulrly, presurgicl evlution of the collecting system nd isthmus is importnt, nd contrst-enhnced CT including CT ngiogrphy is essentil for preopertive evlution of norml ntomy ecuse of the complexity of the isthmic lood supply [9, 2]. Ptients with HSK hve n incresed incidence of renl tumor, such s Wilms, renl pelvic, nd crcinoid tumors [3, 7, 6, 7]. Renl cell crcinom is the most common neoplsm in these ptients ut does not occur more frequently thn in the generl popultion [6, 2]. The incidence of neoplsm in HSK is estimted to e one to 2%, lthough this likely represents the upper limit, in view of the potentil reporting nd selection is [6, 2]. None of our study ptients hd ssocited renl tumor, ut the popultion of our study ws smll. The incidence of tumors of the renl pelvis is pproximtely 3 to 4 greter in ptients with HSK thn with norml kidney configurtion, nd squmous cell crcinom is more common thn urothelil crcinom [6, 7, 2]. The high incidence of squmous cell crcinom is relted to chronic ostruction, urolithisis, nd infection, common complictions of HSK [6, 7]. In this study, wide isthmus is relted to stone formtion. Becuse urolithisis is one of the risk fctor of renl pelvic crcinom, specil ttention should e pid to width of isthmus on CT. Our study hs severl limittions. Our smple ws smll nd included only dults. We evluted width of isthmus only on xil CT imges. And sttisticl difference of incidence of urolithisis etween ptients with wide nd thin isthmus ws smll (P =.48). Error of mesurement on only xil CT imge might hve n influence on the results. We did not perform metolic nlysis of HSK with urolithisis such s serum clcium level nor urinry clcium excretion. Multiplnr imges nd 3-dimensionl ssessment re needed to ssess exct renl shpe including renl rottion. A role of metolic normlities is reported in stone formtion in ptients with HSK [24], nd we suspect ntomic nomly s risk fctor for metolic irregulrity. A lrge-scle study of ptients of ll ges is needed to investigte correltions etween stone formtion, renl shpe, nd metolic nlysis in ptients with HSK. Nevertheless, CT is used routinely in these ptients, nd evlution of renl shpe on xil imge is convenient. In conclusion, we evluted the reltionship etween urolithisis nd chrcteristics of renl shpe of HSK on MDCT in dult ptients nd ptients of HSK with wide isthmus might hve tendency of high incidence of stone formtion. Becuse urolithisis, urinry stsis, nd infection re risk fctors for tumor of the renl pelvis, it is useful to mesure the width of isthmus on xil CT imges nd ttention is more necessry for the progress oservtion of HSK ptients with wide isthmus. REFERENCES ) Cmpell M. 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