双语病例——Blake囊肿

朗读老师：朱勤勤     衢州市人民医院

翻译老师： 温满盈    东莞市大朗医院放射科

审校老师：姜春雷   青岛市第九人民医院

History: A 30-year-old man presents with headache, vertigo, nausea, and visual blurring for the past six months.

男性，30岁，近六个月来头痛、头晕、恶心及视物模糊就诊

A head MRI scan was performed. Axial contrast-enhanced T1-weighted, axial T2-weighted, contrast-enhanced coronal T1-weighted, coronal T2-weighted, and contrast-enhanced sagittal T1-weighted images are shown below. Click to enlarge.

头颅MRI分别是轴位T1增强，轴位T2，冠状位T1增强，冠状位T2，矢状位T1增强。

CT images

A noncontrast-enhanced CT scan performed soon after surgery demonstrated exenteration of the posterior fossa cyst.

CT图像

后颅窝囊肿切除术后CT平扫图像如下

In Blake's pouch cyst, there is vermian hypoplasia.

Patients can be asymptomatic or present symptoms and signs of hydrocephalus.

Blake's pouch cyst appears on MR images as a midline posterior fossa cyst with mural nodule and abnormal enhancement.

Blake囊肿伴有小脑蚓部发育不全。

病人可以无症状或表现为脑积水的症状

Blake 囊肿在MR上表现为伴有壁结节和异常强化的中线后颅窝囊肿

MRI demonstrates a midline posterior fossa cyst, lying below and posteriorly to the vermis cerebellar, with signal intensity similar to that of cerebrospinal fluid (CSF), hypointense on T1 sequences and hyperintense on T2, without abnormal enhancement. The cyst is well-marginated, has a smooth wall, and is unilocular.

The vermis, cerebellar hemispheres, and brainstem are compressed by the cyst due to mass effect but are morphologically normal.

The position of the dural structures (tentorium cerebelli, torcular herophili, falx cerebelli, straight and lateral sinus) and the size of the posterior fossa are normal. There is no rotation of the cerebellum, and there is no accompanied vermian hypoplasia.

There is dilatation of the ventricular system, without periventricular hyperintensities or signs of acute transependymal flow.

CT postsurgery: Noncontrast CT performed soon after surgery demonstrates exenteration of the posterior fossa cyst.

Differential diagnosis

· Blake's pouch cyst

· Dandy-Walker malformation

· Mega cisterna magna

· Posterior fossa arachnoid cyst

Diagnosis: Blake's pouch cyst

MR：MRI表现为中线的后颅窝囊肿，位于小脑蚓部后下部位，同脑脊液信号相似，T1低T2高信号，无强化，囊壁完整、光滑，呈单房。

小脑蚓部、半球及脑干由于占位效应而受压，但形态正常。

硬脑膜结构（小脑幕、窦汇、小脑镰、直窦和侧窦）的位置和后颅窝的大小是正常的，小脑没有翻转，没有蚓部发育不全。

脑室系统扩张，无脑室周围高信号或急性脑室周围渗出的信号

CT术后表现：平扫CT表现为后颅窝囊肿切除术后改变

鉴别诊断

Blake囊肿  Dandy-Walker畸形 大枕大池 后颅窝蛛网膜囊肿

诊断 Blake囊肿

Pathophysiology

There are various classifications and descriptions of collections of cerebrospinal fluid (CSF) in the posterior fossa, which are Dandy-Walker malformation, arachnoid cyst, mega cisterna magna, and persistent Blake's pocket or Blake's pouch cyst.

The persistent BPC is a retrocerebellar cystic malformation thought to derive from persistence and expansion of the normally transient Blake's pouch, which arises from the area membranacea posterior, and usually regresses during the fifth to eighth gestational weeks. It is caused by the absence of fenestration of the Blake pouch, resulting in the lack of communication between the fourth ventricle and the subarachnoid space and leading to tetraventricular hydrocephalus. There is no malformation of the cerebellum and no accompanied vermian hypoplasia.

讨论

病理生理学

针对后颅窝脑脊液的集聚有多种分类和描述，包括Dandy-Walker畸形，蛛网膜囊肿，大枕大池，和永存Blake囊袋或Blake囊肿

Blake囊肿被认为是一种来源于正常且短暂性的Blake陷凹的持续存在并扩张的小脑后囊性畸形。BPC起源于陷凹的后膜部，通常在孕期的第5-8周退化。如果Blake陷凹开窗失败，将会导致第四脑室与蛛网膜下腔缺乏交通，最终形成第四脑室积水。Blake囊肿不伴有小脑畸形和蚓部发育不全。

Clinical presentation

Clinically, Blake's pouch cyst may present with impaired neurological development, progressive hydrocephalus in children of a young age, become symptomatic in adulthood, or remain asymptomatic. In rare instances, Blake's pouch cyst occurs in association with Beckwith-Wiedermann syndrome, cardiac anomalies, and trisomy 21. Clinical manifestations of hydrocephalus are headache, hypotonia, vertigo, syncope, vomiting, blurred or double vision, nystagmus, papilledema, and delayed gait development.

临床表现

临床上，Blake囊肿在儿童期可能表现为神经发育受损及进行性的脑积水，成人症状明显，部分症状不明显。在少量病例中，Blake囊肿的发生与Beckwith-Wiedermann综合征，心脏病，21三体有关。脑积水的临床表现有头痛、肌力减退、头晕、惊厥、呕吐、视物模糊或复视、眼球震颤、视乳头水肿和步态发育迟缓。

Imaging findings

CT is used as a diagnostic method. However, MRI represents the diagnostic modality of choice for the diagnosis and differentiation of posterior fossa collections. It allows assessment of the Sylvius aqueduct for patency, the existence of communication between the fluid collection and the fourth ventricle or the subarachnoid space, and also the search for other associated anomalies in the brain.

Neuroimaging findings include the presence of a cyst in an infraretrocerebellar location, which is essentially a diverticulum of the fourth ventricle, and a constant association with hydrocephalus. The cysts are well-marginated, have a smooth wall, and are nearly always unilocular and located in the midline. Their appearance on CT or MR images is identical to that of cerebrospinal fluid. The vermis, the caudal and medial aspects of the cerebellar hemispheres, and brainstem can be compressed by the cyst due to mass effect but are morphologically normal. There is displacement of the choroid plexus inferior to the vermis along the anterosuperior aspect of the cyst. The displacement of the choroid plexus appears as an enhancing structure on sagittal contrast-enhanced T1-weighted images. The posterior fossa is typically normal in size. Hydrocephalus is always present, but other supratentorial morphologic abnormalities are usually absent.

Blake's pouch cysts have a radiographic aspect similar to an arachnoid cyst. Some authors called Blake's pocket a retrocerebellar arachnoid cyst. However, it is preferable to consider it an entity other than an arachnoid cyst, since its membrane has a distinct ependymal component, as well as a distinct embryological origin. In mega cisterna magna, the absence of hydrocephalus help differentiates it from Blake's pouch cyst, which consistently presents hydrocephalus. In BPC, there is no accompanied vermian hypoplasia, which is commonly present in the Dandy-Walker malformation.

Characteristic radiological features of BPC include the following:

· Tetraventricular hydrocephalus

· Localization of the midline cyst infra or retrocerebellar

· A well-developed, nonrotated cerebellar vermis

· Cystic dilatation of the fourth ventricle without cisternal   communication

· Some degree of compression of the medial cerebellar  hemispheres and brainstem

· Identification of the fourth ventricle choroid plexus in the roof of the cyst on contrast-enhanced MR images

影像表现

CT是一种诊断方法，然而，MR在后颅窝占位的诊断与鉴别诊断当中更有优势，它能评估中脑导水管是否通畅，四脑室或蛛网膜下腔有无积水，还能发现有无脑内的相关异常。

神经影像表现为囊肿位于小脑后下四脑室位置。BPC囊壁完整、光滑，几乎都是单房并且位于中线，它们在CT或MR上的表现同脑脊液相似。小脑半球中间尾部的蚓部和脑干受囊肿挤压但形态正常。四脑室脉络丛的受压移位仅次于位于囊肿前上部的小脑蚓，移位的脉络丛在矢状T1增强上可见强化。后颅窝大小正常。脑积水常见，但是幕上形态异常少见。

BPC影像上跟蛛网膜囊肿相似。有些学者称BPC 为小脑后的蛛网膜囊肿，不过它更应该是一个独立存在的实体，因为它的囊壁有明显的室管膜成分和胚胎来源。大枕大池没有脑积水的表现，可以跟BPC常伴脑积水鉴别开来。BPC不伴有小脑蚓发育不全，而Dandy-Walker畸形常有小脑蚓部发育不全。

BPC影像学特征包括以下几项：

四脑室积水

囊肿位于小脑后下中线位置

四脑室囊性扩张不伴有室间交通

小脑半球中间和脑干受压的程度

在囊肿的根部找到强化的四脑室脉络丛

Treatment

The treatment of choice in the present case was surgical resection of the posterior fossa cyst. After surgery, the patient's clinical condition rapidly improved. Endoscopic third ventriculostomy is a safe and effective treatment option, avoiding the risks of open surgery, as well as many shunt-related problems. The long-term outcome depends on complications related to neurosurgical procedures.

治疗

本例的治疗方案是后颅窝囊肿手术切除。手术后，病人的临床症状明显改善。三脑室内镜造口术也是一种安全有效的治疗方法，可以避免开放手术的风险和许多引流相关的问题。长期效果取决于神经外科手术相关的并发症。