胡桃夹综合征Nutcracker Syndrome

发表者：孙俊杰人已读

胡桃夹综合征(左肾静脉压迫综合征)

胡桃夹综合症是指左肾静脉在腹主动脉和肠系膜上动脉之间受压，这导致左肾静脉压力升高并可能发生侧枝静脉。在临床上，胡桃夹综合征的特征是间歇性血尿，伴或不伴有左腰或腹痛。该综合征发生在相对较瘦的患者，和往往其它方面健康的青少年。胡桃夹综合征的实际发病率仍然不明。

胡桃夹综合征可有多种临床表现。最常见的表现就是血尿。在膀胱镜检查中，左侧输尿管口流出血尿，却没有任何可检测到的尿路畸形，就应该警惕胡桃夹综合征。胡桃夹综合征也可引起轻度至中度的蛋白尿。其他表现罕见，包括性腺静脉综合征和精索静脉曲张。可能发生显著的侧支血管，而且性腺、腰升、肾上腺、输尿管周的和肾囊静脉都是主要的潜在侧支静脉，因左肾静脉受压或阻塞而发生。

产生血尿的机制被认为是由于左肾静脉压力升高，导致小静脉破裂入集合系统或者是扩张的静脉窦与邻近肾盏之间。评估血尿时，当其他病因都被排除后，胡桃夹综合症应该在鉴别诊断中占一席之地。

腹主动脉-肠系膜动脉的距离正常宽度平均值在4和5毫米之间。正常宽的腹主动脉-肠系膜动脉夹角是由腹膜后脂肪和十二指肠的第三部分来维持的。窄的腹主动脉-肠系膜动脉夹角导致左肾静脉受夹或受压。针对腹主动脉-肠系膜动脉夹角缩小，有着这样一个假说，就是体型瘦弱且腹膜后和肠系膜脂肪减少。胡桃夹综合征的其他病因假说，包括后肾下垂结果拉伸了主动脉前的左肾静脉，以及从主动脉发出肠系膜上动脉的异常分支。

如何获得一个可靠的胡桃夹综合征诊断，仍存在争议。肾静脉造影结合左肾静脉和下腔静脉之间的压力梯度测量是显示肾静脉高压的金标准，尽管它对病人来说是侵入性和不舒服的。然而，关于胡桃夹综合征可以明确诊断的压力梯度界值，还没有清楚的一致意见。

多普勒超声测量的左肾静脉前后（AP）径和峰值流速对诊断胡桃夹综合征很有帮助。另一项研究显示，肾静脉下腔静脉压力梯度与彩色多普勒超声中侧支血管流动模式的相关性，会很有助于评估胡桃夹综合征。

CT和CT血管造影是其他无创的方式，可以显示左肾静脉在腹主动脉-肠系膜动脉夹角受压以及侧支静脉。然而，与多普勒超声不同，不能作出侧支血管的流动特性。磁共振成像（MRI）和MR血管造影也可显示肠系膜上动脉和主动脉之间的左肾静脉受压。

静脉肾盂造影及逆行肾盂造影检查常常是正常的。最常见的异常发现是，输尿管或肾盂由于侧支血管的外源性压迫而出现凹痕。

一个混杂因素是左肾静脉扩张是一种正常变异，可以没有侧支静脉且压力梯度正常。在左肾静脉临界高压的患者，区别左肾静脉扩张是一种正常变异还是胡桃夹综合征的早期表现，是很难的。

对于胡桃夹综合征的治疗，还存在争议。对轻度血尿，建议做尿常规检查的保守处理，因为侧支静脉的发展可能解决左肾静脉高血压并缓解症状。手术指征包括：严重的持续性或反复发作性血尿引起贫血，血液凝块导致腹部或腰部疼痛。外科手术选项包括肾切除术，曲张静脉结扎，肾固定和肾静脉下腔静脉再植术。最近，血管内治疗方案也有应用。

Nutcracker Syndrome（left renal vein entrapment syndrome）

Nutcracker syndrome refers to the compression of the left renal vein between the aorta and the superior mesenteric artery, which results in elevated left renal vein pressure and possible collateral vein development. Clinically, Nutcracker syndrome is characterized by intermittent hematuria with or without left flank or abdominal pain. The syndrome occurs in relatively thin patients and adolescents who often have an otherwise healthy medical history. The true prevalence of Nutcracker syndrome remains unknown.

Nutcracker syndrome can have several clinical manifestations. The most common presentation is hematuria. Hematuria from the left ureteral orifice on cystoscopic examination in the absence of any detectable abnormality of the urinary tract should raise suspicion for Nutcracker syndrome.Nutcracker syndrome can also cause mild to moderate proteinuria. Other presentations that are rare include gonadal vein syndrome and varicocele.Prominent collateral vessels may develop, and the gonadal, ascending lumbar, adrenal, periureteral, and capsular veins are major potential collateral veins that can develop from left renal vein compression or obstruction.

The mechanism for producing hematuria is thought to be due to increased left renal vein pressure, resulting in small venous ruptures into the collecting system or between dilated venous sinuses and adjacent renal calyces.Nutcracker syndrome should be part of the differential consideration in the evaluation for hematuria when other etiologies have been excluded.

The aortomesenteric space normally averages between 4 and 5 mm in width.The normally wide aortomesenteric angle is maintained by retroperitoneal fat and the third portion of the duodenum. A narrow aortomesenteric angle causes compression or entrapment of the left renal vein.A hypothesis for the narrowing of the aortomesenteric angle is a thin body habitus with decreased retroperitoneal and mesenteric fat. Other etiologic hypotheses of nutcracker syndrome include posterior renal ptosis with resultant stretching of the left renal vein over the aorta, and abnormal branching of the superior mesenteric artery from the aorta.

Controversy exists about obtaining a reliable diagnosis of nutcracker syndrome. Although it can be invasive and uncomfortable for the patient, renal venography combined with measurement of the pressure gradient between the left renal vein and the IVC is the gold standard for demonstrating renal vein hypertension. However, no clear consensus exists on the cutoff of pressure gradient with which nutcracker syndrome can be clearly diagnosed.

Doppler ultrasound measurements of the anterior-posterior (A-P) diameter and peak velocities of the left renal vein may be helpful in diagnosing nutcracker syndrome.Another study showed that correlation of renocaval pressure gradients with flow patterns from color Doppler sonography in collateral vessels further aids assessment of nutcracker syndrome.

CT and CT angiography are other noninvasive modalities that can demonstrate compression of the left renal vein in the aortomesenteric angle and collateral veins. However, unlike Doppler sonography, flow characteristic cannot be made in collateral vessels. Magnetic resonance imaging (MRI) and MR angiography may also demonstrate the compression of the left renal vein between the superior mesenteric artery and the aorta.

Frequently, intravenous pyelogram and retrograde pyelographic studies are normal. The most common abnormal finding is ureteric or pelvic notching due to extrinsic compression from collateral vessels.

A confounding factor is that distended left renal vein can be a normal variant without collateral veins and with normal pressure gradient. Distinguishing between distended left renal veins that are a normal variant and those that indicate early nutcracker syndrome is difficult inpatientswith borderline left renal vein hypertension.

Controversy also exists regarding treatment of nutcracker syndrome. Conservative management with routine urinalysis is proposed for mild hematuria, since the development of collateral veins may resolve the hypertension in the left renal vein and alleviate symptoms.Indications for surgery include severe persistent or recurrent hematuria causing anemia, and blood clots causing abdominal or flank pain. Surgical options include nephrectomy, variceal ligation, nephropexy, and renocaval reimplantation. More recently, endovascular treatment options have been applied.