15 6月
History: A 75-year-old man presents with headaches.

Axial T2-weighted, fluid-attenuated inversion-recovery (FLAIR), and pre- and post-contrast T1-weighted MR images are shown below.





Q1——There is a lesion in which part of the brain?
A Frontal lobe 额叶
B Temporal lobe 颞叶
C Parietal lobe 顶叶
D Occipital lobe 枕叶
Q2——The lesion contains what signal characteristics?
A Cerebrospinal fluid (CSF)
B Blood
C Mucin 粘液|粘蛋白
Q3——There is some surrounding FLAIR signal abnormality.
A True
B False
Q4——There is enhancement of the lesion.
A True
B False
Q5——This most likely represents a benign(良性的) lesion.
A True
B False
Q6——In what spaces is this lesion found?
A Subarachnoid 珠网膜下
B Subpial 软脑膜下
C Epidural 硬膜外
D Parenchymal 实质的
Q7——What is the most likely diagnosis?
A Arachnoid cyst 蛛网膜囊肿
B Dysembryoplastic neuroepithelial tumor 胚胎发育不良性神经上皮肿瘤
C Dilated perivascular space 扩张血管周围间隙
D Pleomorphic xanthoastrocytoma 多形性黄色星形细胞瘤
Q8——These lesions are never symptomatic有症状的).
A True
B False

Findings and diagnosis






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


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.








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.

  • 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.











  1. 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.
  2. Cherian J, Viswanathan A, Evans RW. Headache and arachnoid cysts.Headache. 2015;54(7):1224-128.
  3. 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.
  4. 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.
  5. Kwee RM, Kwee TC. Virchow-Robin spaces at MR imaging. Radiographics. 2007;27(4):1071-1086.


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