【双语病例】左颞部蛛网膜囊肿1例MR

Q8——These lesions are never symptomatic（有症状的）.

A True

B False

答案1—8：BABB AAAB

Findings and diagnosis

Findings

MRI demonstrates an extra-axial cystic structure in the anterior left temporal lobe. There is no associated abnormal FLAIR signal or enhancement.(MR示左颞角囊性占位；FLAIR信号无异常，无强化)

Differential diagnosis

Arachnoid cyst 蛛网膜囊肿
Epidermoid cyst 表皮样囊肿
Enlarged CSF space (i.e., mega cisterna magna) 脑脊液空间扩大/大枕大池
Subdural hygroma 硬膜下积液
Dilated perivascular space 扩张血管周围间隙
Cystic neoplasms/low-grade gliomas 囊性肿瘤/低级别胶质瘤
- Dysembryoplastic neuroepithelial tumor 胚胎发育不良性神经上皮肿瘤
- Pilocytic astrocytoma 毛细胞型星形细胞瘤
- Pleomorphic xanthoastrocytoma 多形性黄色星形细胞瘤
- Multinodular and vacuolating neuronal tumor 多结节和空泡神经肿瘤
Cystic periventricular leukomalacia 囊变的脑室周围白质软化

Diagnosis

Arachnoid cyst

Key points

Clinical presentation/pathophysiology

Arachnoid cysts are thought to be diverticula emanating from septations of arachnoid membranes, connected to the subarachnoid space and filled with CSF fluid.
They are benign, usually developmental anomalies (some having genetic associations), but they can also arise as a result of prior trauma, infection, or hemorrhage.
They are reported to be found in approximately 1.4% of individuals (Al-Holou et al, 2013).
Arachnoid cysts can occur anywhere in the subarachnoid space, including within the spinal canal.
Occasionally, they can enlarge and cause mass effect on nearby structures leading to neurological symptoms such as headache and cranial nerve dysfunction, including hearing loss. They can also lead to noncommunicating hydrocephalus.
There is a weak link between middle cranial fossa arachnoid cysts and chronic subdural hematomas. This is believed to be due to moving fluid in the cysts, increasing the risk of tearing of small bridging vessels.
They can rupture and hemorrhage after head trauma.

蛛网膜囊肿被认为是从蛛网膜分隔产生囊腔，与蛛网膜下腔相通和充满脑脊液；

良性的，通常是发育异常（某些具有遗传相关性），但它们也可能因创伤、感染或出血而引起；

据报道，大约有1.4%的人可见；

可发生在任何地方，包括椎管内。

偶尔，他们会扩大并对附近的结构造成占位效应，导致神经系统症状，如头痛和颅神经功能障碍，包括听力损失；也可导致梗阻性脑积水。

中颅窝蛛网膜囊肿与慢性硬膜下血肿之间存在薄弱环节；由于在囊肿内的移动流体，增加小血管撕裂的风险。

外伤后可破裂出血。

Imaging features

Arachnoid cysts appear as well-circumscribed extra-axial cysts with thin/imperceptible walls arising from the subarachnoid space.
They can be seen anywhere in the subarachnoid space, including middle cranial fossa (34%), retrocerebellar (33%), cerebral convexity, quadrigeminal cistern, suprasellar cistern, and ventricles (Al-Holou et al, 2013).
They can also be found in the spine, usually dorsal to the cord in the thoracic region.
They follow CSF signal characteristics on all sequences.
Arachnoid cysts do not show abnormal enhancement.
They do not show restriction of diffusion, but they may occasionally show slightly higher signal intensity on diffusion secondary to stasis. In contrast epidermoid cysts will show diffusion restriction.
High-resolution constructive interference in steady-state (CISS) and fast imaging employing steady-state acquisition (FIESTA) sequences can help delineate cyst walls.
Phase contrast imaging can help determine point of communication with subarachnoid space.
They can gradually enlarge and cause local mass effect and bone remodeling (as seen by thinning and scalloping on CT).
Ultrasound is useful for diagnosing and characterizing arachnoid cysts during the third trimester and the first year of life. On ultrasound, arachnoid cysts appear as regular-shaped, hypoechoic structures with no color flow.

Treatment/prognosis

Arachnoid cysts are usually incidental lesions that do not require treatment.
They can usually be followed up with additional imaging to ensure stability.
In some cases, treatment will be indicated when they become locally compressive and correlate with neurologic symptoms.
They can be treated by craniotomy with excision or fenestration of the cyst, or by placement of a cystoperitoneal shunt.
These procedures usually relieve symptoms and have relatively low morbidity/mortality.

蛛网膜囊肿表现为起源于蛛网膜下腔，边界清晰的轴外囊肿，囊壁薄。

可以发生在蛛网膜下腔的任何地方，包括颅中窝（34%）、小脑后（33%）、大脑凸面、四叠体池、鞍上池，和侧脑室。

也可以在脊柱上发现，通常在胸段脊髓背侧。

在所有序列上表现为脑脊液信号特征；增强无强化；

弥散不受限，但偶尔会显示弥散上轻微的高信号；相对的，表皮样囊肿弥散受限。

在稳态高分辨率干涉（CISS）和稳态进动快速成像序列（FIESTA）可以帮助界定的囊壁。

相位对比成像可帮助确定与蛛网膜下腔的交通点。

可逐渐增大并引起局部的占位效应和骨重塑。

在孕晚期和出生第一年，超声有助于诊断和描述蛛网膜囊肿的特症，超声上显示为形状规则的无彩色血流的低回声结构。

References

Al-Holou WN, Terman S, Kilburg C, Garton HJ, Muraszko KM, Maher CO. Prevalence and natural history of arachnoid cysts in adults. J Neurosurg. 2013;118(2):222-231.
Cherian J, Viswanathan A, Evans RW. Headache and arachnoid cysts.Headache. 2015;54(7):1224-128.
De Keersmaecker B, Ramaekers P, Claus F, et al. Outcome of 12 antenatally diagnosed fetal arachnoid cysts: Case series and review of the literature. Eur J Paediatr Neurol. 2015;19(2):114-121.
Epelman M, Daneman A, Blaser SI, et al. Differential diagnosis of intracranial cystic lesioss at head US: Correlation with CT and MR imaging.Radiographics. 2006;26(1):173-196.
Kwee RM, Kwee TC. Virchow-Robin spaces at MR imaging. Radiographics. 2007;27(4):1071-1086.

Q1——There is a lesion in which part of the brain?

Q2——The lesion contains what signal characteristics?

Q3——There is some surrounding FLAIR signal abnormality.

Q4——There is enhancement of the lesion.

Q5——This most likely represents a benign（良性的） lesion.

Q7——What is the most likely diagnosis?

Q8——These lesions are never symptomatic（有症状的）.