胎兒腸梗阻的MRI診斷

周立霞，卜靜英，耿左軍，李海燕，劉慈，李索林

胎兒腸梗阻的MRI診斷

周立霞1*，卜靜英1，耿左軍1，李海燕2，劉慈2，李索林3

目的觀察胎兒期腸梗阻MRI表現(xiàn)，結合生后手術史及病理學診斷，探討MRI對胎兒期腸梗阻的診斷價值。材料與方法回顧性分析胎兒期腸梗阻病例26例，胎齡為孕23～35 w，均先行胎兒超聲檢查后再行胎兒MRI平掃。采用2D快速平衡穩(wěn)態(tài)進動序列(2D fast imaging employ steady acquisition， 2D FIESTA)、單次激發(fā)快速自旋回波(single-shot fast spin echo，SSFSE)序列、快速反轉恢復運動抑制序列T1WI (fast inversion recovery motion insensitive T1WI，F(xiàn)IRM T1WI)和彌散加權成像(diffusion weighted imaging，DWI)序列。根據(jù)梗阻部位、梗阻區(qū)腸管信號改變、梗阻遠端腸道充盈情況、腸系膜血管異常等進行影像學診斷，并觀察繼發(fā)改變?nèi)绺顾⒀蛩龆嗟龋S訪出生情況及手術治療結果，分析MRI診斷的正確率及漏診率，探討MRI各序列在胎兒腸梗阻診斷中的優(yōu)勢。結果26例腸梗阻胎兒中：十二指腸/空腸狹窄或閉鎖16例，其中4例伴十二指腸和空腸旋轉不良；胎糞性小腸梗阻4例，其中2例繼發(fā)腸扭轉致腸缺血壞死；肛門閉鎖4例；結腸狹窄或閉鎖1例；先天性巨結腸1例。所有胎兒均伴有不同程度羊水增多，部分病例伴腹水、心包積液及睪丸鞘膜積液；2例為單臍動脈。MRI診斷正確率為92.3%(24/26)，誤診率為7.7%(2/26)。MRI能清楚顯示胎兒腸梗阻部位，觀測腸管擴張的程度。SSFSE序列可顯示系膜血管受累，F(xiàn)IRM T1WI序列有助于結腸梗阻的診斷，DWI序列可提示梗阻腸管缺血和出血的改變。結論胎兒期腸梗阻MRI圖像有特征性改變，可以判斷受累腸管的發(fā)生部位、梗阻程度和合并癥等，對產(chǎn)前診斷和出生后手術治療有重要參考價值。

胎兒疾病；磁共振成像；腸梗阻；彌散加權成像；腸扭轉

周立霞, 卜靜英, 耿左軍, 等. 胎兒腸梗阻的MRI診斷. 磁共振成像, 2017, 8(2): 125-130.

胎兒期腸梗阻是比較常見的先天性腸道異常，產(chǎn)前診斷對評估預后和生后手術治療至關重要。產(chǎn)前超聲是胎兒檢查的主要影像學方法，近年來隨著胎兒MRI普及，MRI已經(jīng)成為產(chǎn)前畸形篩查的有力補充。胎兒MRI圖像分辨率高，能提供更豐富、準確的診斷信息，逐漸被臨床重視。本文對26例先天性腸梗阻胎兒的MRI影像表現(xiàn)進行分析，探討其在產(chǎn)前診斷和生后治療中的價值。

1 材料與方法

1.1 研究對象

2014年9月至2016年2月，在我院行胎兒MRI診斷腸管擴張，提示腸梗阻者26人，均先行胎兒超聲檢查，并于產(chǎn)后隨訪手術或病理證實。孕婦年齡22～35歲，平均年齡(27.00±0.73)歲；胎兒孕周23～35 w，平均孕周(29±2) w。

1.2 儀器與方法

MRI檢查及診斷：應用GE 1.5 T Signa Excite 1.5 T超導型磁共振儀，相控陣8通道體部線圈。孕婦取仰臥位，通過快速定位序列調(diào)整線圈中心位于胎兒腹部。采集胎兒橫斷面、矢狀面及冠狀面。采用4個序列包括2D快速平衡穩(wěn)態(tài)進動序列(2D fast imaging employ steady acquisition，F(xiàn)IESTA)、單次激發(fā)快速自旋回波(single-shot fast spin echo，SSFSE)序列、快速反轉恢復運動抑制序列T1WI (fast inversion recovery motion insensitive T1WI，F(xiàn)IRM T1WI)、彌散加權成像(diffusion weighted imaging，DWI)。掃描層厚5～6 mm，層間距-2～0 mm。

所有MRI圖像均由2位以上高年資醫(yī)師進行會診后再出具影像學報告。小腸梗阻及結腸梗阻診斷標準：24 w前小腸內(nèi)徑超過 4 mm，結腸內(nèi)徑超過 7 mm；24 w后小腸內(nèi)徑超過 7 mm，結腸內(nèi)徑超過 18 mm。

1.3 隨訪

所有胎兒均于產(chǎn)后追蹤隨訪，10例引產(chǎn)胎兒經(jīng)尸檢證實，16例生后手術治療，收集手術記錄及病理資料。

1.4 統(tǒng)計學分析

結合隨訪結果分析MRI對胎兒腸梗阻診斷的正確率和誤診率。

2 結果

2.1 胎兒腸梗阻的MRI表現(xiàn)及隨訪結果

2.1.1 16例十二指腸或空腸近段狹窄或閉鎖

MRI表現(xiàn)均為十二指腸管腔明顯擴張，胃泡擴大。3例十二指腸閉鎖，梗阻部位遠端腸管內(nèi)液體充盈明顯減少(圖1A、B)。2例空腸近端狹窄者伴旋轉不良，MRI顯示擴張的十二指腸及部分空腸腸管位于右上腹部，梗阻處見“鳥嘴征”(圖1C、D)。10例于新生兒期行手術治療，6例引產(chǎn)后尸檢。

2.1.2 4例胎糞性小腸梗阻

MRI示小腸梗阻，3例伴腹水。2例引產(chǎn)者伴胎糞性腹膜炎。2例生后手術治療，其中1例胎兒分別于孕33 w、35 w各行MRI檢查一次，腸管寬度由18 mm增加至22 mm，提示腸梗阻程度加重，于38 w出生，產(chǎn)后2 d行手術治療，術中見梗阻位于空腸遠段。MRI示手術胎兒兩次檢查圖像，孕33 w (圖2A～2C)見梗阻區(qū)腸袢顯著擴張，腸管排列異常可見漩渦征(圖2A)。部分腸壁水腫增厚(圖2B長箭)，部分腸壁變薄(圖2B箭頭)。孕35 w (圖2D、E)見腸管擴張較前顯著，腸內(nèi)容物呈稍短T1長T2信號，提示腸腔內(nèi)出血可能(圖2C、D)。SSFSE序列見梗阻腸管間隙近腸系膜側低信號的系膜血管扭曲、聚攏(圖2C)。DWI序列顯示病變區(qū)腸管管壁及管腔內(nèi)見不均勻混雜信號，以高信號為主(圖2E長箭)，可見多發(fā)斑片狀低信號(圖2E箭頭)。于孕38 w順產(chǎn)后第2天行開腹探查術，術中見部分空腸扭轉且缺血壞死，腸腔內(nèi)容物呈黑褐色，梗阻遠端見質(zhì)地較硬的胎糞阻塞(圖2F)。引產(chǎn)后尸檢示2例回腸梗阻，1例位于空腸梗阻，1例位于回盲部。

2.1.3 4例先天性肛門閉鎖

MRI顯示結腸全程擴張，直腸為主，近肛門處呈盲端樣改變。伴小腸輕度擴張及胃泡擴大(圖3A～D)，2例伴腹水。均隨訪證實，其中2例引產(chǎn)，2例于生后在外院行手術治療。

2.1.4 1例結腸狹窄或閉鎖

MRI示結腸普遍擴張(圖4A～D)，表現(xiàn)為T1WI高信號的結腸明顯增粗，乙結腸遠端狹窄，且直腸較細，近側小腸管腔未見明顯擴張。此例胎兒引產(chǎn)經(jīng)尸檢證實為乙狀結腸遠端狹窄。

2.1.5 1例先天性巨結腸

表現(xiàn)為橫結腸囊樣擴張，遠端可見局限性萎陷，降結腸、乙狀結腸及直腸管腔及信號正常(圖5A～C)，生后證實為節(jié)段性巨結腸。

2.2 26例胎兒MRI診斷、隨訪情況

26例腸梗阻胎兒，24例診斷正確，2例肛門閉鎖MRI誤診為先天性巨結腸，無漏診。正確率為92.3%(24/26)，誤診率為7.7%(2/26)。見表1。

3 討論

胎兒期疾病的首選檢查方法為胎兒超聲，近年來，隨著MRI技術的發(fā)展，胎兒MRI逐漸應用于產(chǎn)前診斷胎兒期各系統(tǒng)疾病[1]。目前對胎兒期腸管病變的檢查仍以超聲為主，MRI在胃腸道疾病的報道較少。

表1 26例胎兒腸梗阻MRI診斷及隨訪Tab.1 MRI diagnosis and follow up of 26 cases of fetal intestinal obstruction

3.1 MRI對胎兒腸梗阻部位的判斷

當胎兒超聲發(fā)現(xiàn)腸管擴張，并且伴羊水增多或腹水，則提示存在腸梗阻可能[2-4]。胎兒MRI判斷梗阻部位主要根據(jù)腸管分布、形態(tài)和腸管信號的改變。(1)根據(jù)消化道的解剖學分布判斷梗阻位置：如左上腹小腸擴張的常為空腸梗阻，右下腹則多見于回腸。肛門閉鎖造成的梗阻表部位全結腸顯著擴張，同時伴有小腸彌漫輕度擴張(圖5)。應同時結合整個消化道的分布判斷是否存在腸旋轉不良。(2)根據(jù)梗阻腸管形態(tài)判斷梗阻部位：十二指腸遠端或空腸近端梗阻時，胃泡和十二指腸球擴大出現(xiàn)“雙泡征”[5-6]。巨結腸造成的梗阻會見到擴張段、移行段和狹窄段。肛門閉鎖者梗阻的直腸遠端呈“盲端樣”改變，通過影像學估測肛門閉鎖位置，有利于生后手術方式的選擇[7]。

(3)根據(jù)梗阻腸管信號判斷的梗阻部位：在胎兒期，根據(jù)腸內(nèi)容物的MRI信號，可以判斷梗阻部位。這是因為食管、胃和大部分小腸的內(nèi)容物為羊水，呈長T1長T2信號；而末段小腸及結直腸內(nèi)主要內(nèi)容物為胎糞，胎糞內(nèi)的礦物質(zhì)如銅、鐵和錳等金屬物質(zhì)有順磁性效應，可縮短T1時間，呈T1高信號；而且這些物質(zhì)因造成磁場不均縮短T2時間，因此呈T2WI低信號[8-9]。

3.2 胎兒期腸梗阻病因的推斷

文獻報道胎兒腸梗阻最常見的原因為腸道閉鎖或狹窄，以肛門閉鎖最多見[10]。本組病例中肛門閉鎖胎兒(4例)少于十二指腸及空腸近段狹窄/閉鎖(16例)，可能由于后者梗阻位置較高，羊水增多明顯，更有利于早期發(fā)現(xiàn)梗阻。胎糞性腸梗阻也是較多見的原因之一[11-12]，本組病例中胎糞性腸梗阻4例，其中1例胎兒生后手術中見梗阻腸管末端見到胎糞團塊，腸管過度擴張，同時腸扭轉繼發(fā)腸系膜血管缺血。嚴重的胎糞性梗阻可以出現(xiàn)腸管破裂穿孔、胎糞性腹膜炎、腹水等。胎糞性腹膜炎是一種無菌化學性炎癥，有時腸管破口能自行修復，炎癥得以緩解，腹水逐漸吸收，但有些新生兒CT檢查仍可見腹膜腔殘存的包裹性腹水及散在鈣化[13]。胎兒期，有些肛門直腸畸形難以準確診斷，尤其是短節(jié)段型巨結腸不易與肛門閉鎖鑒別，二者都可以表現(xiàn)為局部結腸擴張，遠側直腸變細。先天性巨結腸為動力性梗阻，排空延遲，小腸和胃泡多無明顯擴張；而結腸閉鎖/狹窄則可以導致近側小腸、胃泡甚至食管的擴張。由于難以顯示胎兒體表結構，本組2例肛門閉鎖誤診為巨結腸，因此仍需要結合超聲檢查。綜上所述，胎兒期腸梗阻病因的推斷應綜合梗阻部位、梗阻區(qū)腸管的信號、梗阻遠端腸管充盈情況、腸系膜血管的信號變化等綜合分析。

圖1 A、B (FIESTA)：孕35 w胎兒，十二指腸遠端梗阻。胃泡及十二指腸顯著擴張(A箭)，十二指腸遠側近空腸處狹窄呈“鳥嘴征”(B箭)；C、D (FIESTA)：孕34+6w胎兒，空腸梗阻。胃泡、十二指腸及近端空腸擴張，十二指腸及空腸位于右上腹(C箭)，提示存在旋轉不良。梗阻部位空腸鳥嘴樣狹窄(D箭) 圖2 A、B：FIESTA，C：SSFSE，D：FIRM T1WI，E：DWI (b=700 s/mm2)：同一胎兒孕33 w (A～C)和孕35 w (D、E)，胎糞性腸梗阻。超聲診斷小腸局部腸管擴張，羊水顯著增多。孕33 w胎兒腹腔內(nèi)見一明顯擴張的腸袢(A箭)，腸管擴張腸壁部分增厚(B箭)，部分明顯變薄(B箭頭)，于SSFSE序列可見腸系膜區(qū)血管聚攏、扭曲(C箭)。隨著孕周增大，梗阻程度加重。孕35 w FIRM T1WI序列見梗阻的腸腔內(nèi)為短T1高信號(D箭)。DWI示腸壁高信號(E箭)，腸腔內(nèi)信號混雜，可見多發(fā)斑片狀低信號(E箭頭)。生后第2天開腹探查見梗阻腸管破裂，病變腸袢呈灰黃色提示缺血壞死(F箭)Fig. 1 A, B (FIESTA): A fetus at 35 weeks 4 days' gestation, distal duodenal obstruction. Stomach and duodenum was significantly dialated (A, arrow), a narrow segment existed at distal duodenal adjacent to jejunum as "beak sign" (B, arrow); C, D (FIESTA): A fetus at 34 weeks and 6 days' gestation with jejunum obstruction. Stomach, duodenum and proximal jejunum were expanded, duodenum and jejunum located in the right upper quadrant (C, arrow), suggested bowel malrotation. Obstructed jejunum was narrow as beak sample (D, arrow). Fig. 2 A, B: FIESTA, C: SSFSE, D: FIRM T1WI, E: DWI (b=700 s/mm2): A fetus at 33 weeks and 35 weeks of gestation with meconium ileus. Ultrasonic diagnosis partial bowel of small intestinal expansion, amniotic fluid significantly increased. At 33 weeks a significant expanded bowel loops existed within fetal abdomen (A, arrow) and part bowel wall was thickening (B, arrow), or thinner than normal (B, arrow head). Mesenteric vessels twisted on SSFSE imaging. (C, arrow). The obstruction was getting worse with the pregnant weeks past. The obstructed lumen showed short T1 and high signal on FIRM T1WI (D, arrow). DWI showed intestinal wall high signal (E, arrow), mixed signal was on lumen contents with multiple patchy low signal (E, arrow head). The obstructed bowel was seen ruptured during laparotomy exploration on the second day after birth, the bowel loop was gray and suggesting ischemic necrosis (F, arrow).

圖3 A～C：FIESTA，D：FIRM T1WI，孕31 w胎兒，生后證實肛門閉鎖。直腸遠端為盲端(A、B箭)，近側結直腸顯著擴張(C、D箭)，小腸管腔輕度增寬(C箭頭)，肝周見少量腹水(B箭頭)。FIRM T1WI序列示增粗的橫結腸為高信號(D箭) 圖4 A：FIESTA，B：DWI (b=0)，C：SSFSE，D：FIRM T1WI，孕32 w胎兒結腸狹窄。MRI示結腸普遍擴張，呈短T1短T2信號(A～C長箭)，乙狀結腸遠端狹窄(A短箭)。直腸顯著變細(D箭) 圖5 A：FIRM T1W，B、C：FIESTA，孕29 w胎兒，先天性巨結腸伴旋轉不良。右上腹橫結腸狀擴張，其遠側腸管局限性萎陷(A～C箭)，直腸形態(tài)正常Fig. 3 A—C: FIESTA, D: FIRM T1WI, A 31 weeks gestation fetus, confirmed anal atresia after birth. Distal rectum was cecum (A, B, arrow), the proximal colorectal expanded (C, D, arrow), and the small intestine was also mildly broadening (C, arrow head), and ascites was shown around liver (B, arrow head). The expanded transverse colon was high signal in FIRM T1WI (D, arrow). Fig. 4 A: FIESTA, B: DWI (b=0), C: SSFSE, D:FIRM T1WI, A fetus at 32 weeks gestation with colon stenosis. The colon was extensive expanded and showed short T1 short T2 signal (A—C, long arrow) with distal sigmoid colon stenosis (A, short arrow). The rectum significantly thinner (D, arrow). Fig. 5 A: FIRM T1W, B, C: FIESTA, A fetus at 29 weeks gestation with congenital megacolon and malrotation. The transverse colon in right upper quadrant expanded and the distal bowel stenosis (A—C, arrow), the colon was in normal form.

3.3 MRI快速序列在胎兒腸梗阻診斷中的應用

胎兒MRI多采用快速序列，逐層采集圖像，約每1～2 s掃描1層，每個序列控制在20余秒左右，從而達到“凍結胎動”的效果[1，14]。本組胎兒腸梗阻病例主要應用FIESTA、SSFSE、FIRM T1WI和DWI 4個快速MRI序列，各序列在診斷中各有優(yōu)劣，逐一分析如下：(1)FIESTA序列為最常用的“白血”序列，成像速度最快，信噪比高，有利于觀察解剖結構。(2)SSFSE序列是快速T2WI成像序列。腸管內(nèi)因含羊水為長T2高信號，而結直腸因含有胎糞為低信號對判斷腸梗阻部位有幫助[15]。另外，SSFSE序列也稱為“黑血”序列，有助于腸扭轉及腸缺血時腸系膜腸管的觀察。(3)孫 子燕等[16]發(fā)現(xiàn) 在 孕32 w 后 ，小腸 末 端高信號減少甚至消失，僅結腸為T1WI高信號，因此T1WI有助于顯示胎兒正常結腸及先天性結腸病變。本研究應用FIRM T1WI序列發(fā)現(xiàn)先天性巨結腸、肛門閉鎖等結直腸畸形。胎兒MRI圖像中T1高信號不一定是末端或結腸，在有些疾病，胎兒小腸亦可呈T1高信號，如遺傳性腹瀉、囊性纖維化，短結腸畸形等[17]。本組病例中，胎糞性腸梗阻累及的小腸為短T1高信號(圖2D)，考慮為胎糞梗阻后繼發(fā)腸扭轉和缺血壞死，導致腸腔內(nèi)出血、大量炎性細胞和蛋白積聚，順磁性物質(zhì)含量增高縮短T1時間所致，此種情況則需要結合腸管分布及多序列綜合判斷。(4)DWI序列成像速度快，也是常用的胎兒MRI序列。本研究發(fā)現(xiàn)正常胎兒小腸及結直腸DWI序列均呈低信號，但是當存在腸缺血梗死時，受累腸壁及腸腔內(nèi)可表現(xiàn)為不均勻高信號。腸壁高信號可能與缺血壞死所致的細胞毒性水腫有關。當腸管壞死時，腸腔內(nèi)存在出血、炎性細胞浸潤和蛋白積聚導致局部水分子擴散受限，產(chǎn)生DWI高信號。由于出血時期不同，T2透過效應的影響，導致腸腔內(nèi)DWI信號不均(圖2E)。

總之，胎兒MRI應用多種快速成像序列，對胎兒期腸梗阻的定位及病因診斷更準確。有利于評估預后，為產(chǎn)科和新生兒外科醫(yī)生提供參考。

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The MRI diagnosis of fetal intestinal obstruction

>ZHOU Li-xia1*, BU Jing-ying1, GENG Zuo-jun1, LI Haiyan2, LIU Ci2, LI Suo-lin3

1Department of Medical Imaging, the Second Hospital of Hebei Medical University, Shijiazhuang 050000, China

2Department of the Seventh Gynecology, the Second Hospital of Hebei Medical University, Shijiazhuang 050000, China

3Department of Pediatric Surgery, the Second Hospital of Hebei Medical University, Shijiazhuang 050000, China

*Correspondence to: Zhou LX, E-mail: doctorzhou@126.com

Received 31 May 2016, Accepted 2 Aug 2016

Objective:To observe fetal intestinal obstruction with MRI, compared with the result of newborn surgery and pathology, explore the value of MRI in the diagnosis of fetal intestinal obstruction.Materials and Methods:Twenty-six cases of fetal intestinal obstruction were retrospectively analyzed, gestational age was 23—35 w, all cases were performed fetal ultrasound before fetal MRI. 4 MRI sequences were used including 2D FIESTA (2D fast imaging employ steady acquisition), SSFSE (single-shot fast spin echo), FIRM T1WI (fast inversion recovery motion insensitive T1WI) and DWI (diffusion weighted imaging). According to the intestinal obstruction sites, bowel signal changes, distal intestinal filling, and mesenteric vessels changes, radiological diagnosis was made, the secondary imaging signs such as ascites and amniotic fluid were also observed. Follow-up the fetal birth and surgical treatment postnatal , analysed the MRI accuracy and the missed diagnosis rate, and investigated the advantage of each sequence in the diagnosis of fetal intestinal obstruction.Results:In the 26 cases of fetal intestinal obstruction, 16 cases were duodenum/jejunum stricture or atresia with 4 cases accompanied duodenum and jejunum malrotation, 4 cases were small intestinal meconium obstruction with 2 cases secondary volvulus and ischemia necrosis, 4 cases were anal atresia, 1 case was colonic stricture or atresia and 1 case was congenital megacolon. All fetuses were associated with amniotic fluid in different degree, some cases with pleural effusion, pericardial effusion and hydrocele testis. 2 cases with single umbilical artery. MRI diagnostic accuracy rate was 92.3% (24/26), the misdiagnosis rate was 7.7% (2/26). MRI can locate the fetal intestinal obstruction and observe the extent of bowel dilatation. SSFSE can clearly show mesenteric vessels, FIRM T1WI is helpful to diagnosis of colonic ileus, DWI can detect obstruction ischemic bowel through the intestinal signal.Conclusion:Fetal intestinal obstruction has characteristic radiological imaging, the obstruction site and cause can be judged through fetal MRI as well as the complications, which has important reference value for prenatal diagnosis and postnatal surgical treatment.

Fetal diseases; Magnetic resonance imaging; Intestinal obstruction; Diffusion weighted imaging; Volvulus

1.河北醫(yī)科大學第二醫(yī)院醫(yī)學影像科，石家莊 050000

周立霞，E-mail：doctorzhou@126. com

2016-05-31

R445.2；R722.19

A

10.12015/issn.1674-8034.2017.02.010

2.河北醫(yī)科大學第二醫(yī)院婦七科，石家莊 050000

3.河北醫(yī)科大學第二醫(yī)院小兒外科，石家莊 050000

接受日期：2016-08-02