arachnoid cyst

there are collection of imaging and history

1. Cerebral cyst Khazaei mojtaba , fellowship of neurovascular intervention

2. Arachnoids' cyst relatively common. benign and asymptomatic. There are within the intracranial compartment. ( most common) and the spinal canal.  located within the subarachnoid space  . contain   CSF.  

3. Arachnoids' cyst majority are sporadic. seen with increased frequency. in  mucopolysaccharidoses (as are perivascular spaces ).

4. Clinical presentation of Arachnoids' cyst Approximately 5% of patients experience symptoms. result of gradual enlargement resulting in mass effect. This results in either direct neurological dysfunction or distortion of normal CSF pathways resulting in obstructive hydrocephalus.  Sellar/ suprasellar , quadrigeminal, and cerebellopontine angle arachnoid cysts were more likely to be symptomatic.

5. Radiographic features of arachnoid cyst can occur anywhere within the central nervous system. most frequently (50-60%) located in the middle cranial fossa .  retrocerebellar location accounts for 30-40%  suprasellar cistern within the ventricles posterior fossa cisterna magna (need to be distinguished from a mega cisterna magna) cerebellopontine angle (need to be distinguished from an epidermoid cyst) spinal canal

6. MRI of arachnoid cyct follow CSF on all sequences , isplacement of surrounding structures no solid component, no enhancement Phase contrast imaging: determine if the cyst communicates with the subarachnoid space high resolution sequences such as CISS & FIESTA help to delineate cyst wall and adjacent anatomic structures.

7. Treatment and prognosis of arachnoid cyst majority remain asymptomatic throughout life . If they are deemed to be causing symptoms, then surgery can be contemplated. rare complication is spontaneous rupture in the subdural space .

8. Differential diagnosis of arachnoid cyst enlarged CSF space (e.g. mega cisterna magna) epidermoid cyst o ften shows a heterogeneous/dirty signal on FLAIR restricted diffusion more lobulated   tend to engulf adjacent arteries and cranial nerves subdural hygroma /chronic subdural hemorrhage do not typically show CSF signal intensity on MRI , can have an enhancing membrane cystic tumors: often will have a solid/enhancing component and be intra-axial pilocytic astrocytoma Hemangioblastoma non- neoplastic cysts neurenteric cyst neuroglial cyst porencephalic cyst often follow a history of trauma or stroke surrounded by gliotic brain   neurocysticercosis small cyst, usually multiple when in the subarachnoid space

9. Arachnoid cyst Arachnoid cyst  of the middle cranial fossa . Note the remodelling of the lateral wall of the right middle cranial fossa on bone window CT.

10. Arachnoid cyst - parafalcine MRI images demonstrate a left posterior parafalcine cyst overlying the precuneus that follows CSF signal on all sequences. Features are those of an  arachnoid cyst .

11. Arachnoid cyst - posterior fossa MRI through the posterior fossa demonstrates a large right-sided extra-axial CSF intensity mass lesion. It follows CSF on all sequences, including FLAIR. There is significant mass effect on the adjacent cerebellar tissue and remodelling and expansion of the adjacent skull is evident.  High resolution T2 images (FIESTA) demonstrates that this lesion is bounded by a very thin membrane, best seen bulging across the midline towards the left.  Sagittal images demonstrate upward bowing and thinning of the corpus callosum suggesting hydrocephalus. 

12. Arachnoid cysts causing proptosis Large middle cranial fossa   arachnoid cyst  expanding the bone and deforming the posterolateral wall of the orbit resulting in proptosis . The arachnoid cyst extends inferiorly into the pterygoid process (open arrow).

13. Arachnoid cyst - middle cranial fossa A region of CSF intensity which expands the middle cranial fossa and displaces the temporal lobe posteriorly . There is no restricted diffusion, no solid component and no enhancement. Features are characteristic of an  arachnoid cyst . 

14. Arachnoid cyst – spinal Female with LBP The thoracic spinal cord (C) is displaced anteriorly by a CSF intensity space which on axial imaging in fact has slightly higher and more homogeneous signal than one normal sees in thoracic CSF. 

15. Arachnoid cyst - posterior fossa Large posterior fossa   arachnoid cyst  (note it follows CSF signal on both T1 and T2) with mass effect. 

16. Arachnoid cyst of the posterior fossa with hydrocephalus Large posterior cranial fossa CSF intensity space consistent with an  arachnoid cyst  displaces the cerebellum anteriorly resulting in marked  obstructive hydrocephalus . Note the ballooning of the third ventricular recesses and the upward displacement of the corpus callosum . 

17. Arachnoid cyst - cerebellopontine angle Right  cerebellopontine angle  CSF density space with mass-effect on the adjacent cerebellar hemisphere and remodelling of the overlying bone consistent with an  arachnoid cyst . The only viable differential is that of an epidermoid cyst which is far less likely given the very homogeneously exactly-CSF density and the presence of bony remodelling absent in epidermoid cysts. An MRI would be required to categorically confirm this. 

18. Arachnoid cyst – suprasellar cont.. MRI demonstrates a CSF intensity space distorting the optic chiasm and pituitary infundibulum (pushing them forwards and upwards). A thin membrane can be seen (best on sagittal and axial T2 weighted images) invaginating upwards into the third ventricle, splaying the septum pellucidum and even bulging into the left foramen of Munro. The lateral ventricles are dilated, in keeping with  obstructive hydrocephalus , clearly long standing (note large size and lack of transependymal edema). 

19. Arachnoid cyst - suprasellar Anterior cerebral arteries and basilar artery tip are seen as flow voids (red arrows); optic chiasm (yellow arrow); pituitary infundibulum (orange arrow); septum pellucidum (green dotted lines); arachnoid cyst (blue dotted line).  A third ventriculostomy was performed, and the floor of the cyst was also opened into the interpeduncular cistern. Prominent CSF pulsation can be seen continuously from the third ventricle to the prepontine cistern.  Note the reduced distortion on the optic chiasm and pituitary infundibulum . 

20. Arachnoid cyst – frontal lob  with overlying bony remodelling

21. Arachnonid cyst Large extra-axial CSF-density centered on the middle cranial fossa . Mass effect onto the adjacent brain. 

22. Arachnoid cyst with headache A large cystic lesion that follows CSF signal on all pulse sequences representing an arachnoid cyst.

23. Arachnoid cyst distorting the third ventricle Case Discussion Hydrocephalus was  secondary to an obstructive third ventricle cyst.VP shunt tube in situ. The MR appearance suggests a suprasellar   arachnoid cyst  displacing the chiasm and infundibulum anteriorly however on endoscopy the arachnoid cyst was (apparently) actually intraventricular in location, within the third ventricle. 

24. Case Discussion CT and MR images demonstrate a hemorrhagic arachnoid cyst

25. Arachnoid cyst - cerebellopontine angle Right sided vertigo ? CSF intensity cystic lesion in the right cerebellopontine angle. It follows CSF signal in all the sequences. The lesion does not show restricted diffusion, excluding an epidermoid cyst. Cerebellar hemispheric compression ( sagittal series) and distortion of the brain stem with anterior displacement and stretching of the VII/ VIIIth and XIIth nerves.

26. Supravermian arachnoid cyst 50 year old F Headaches. Unexplained weakness of the right arm. Homogeneous lesion between the upper vermis and the cerebellar tentorium with homogeneous CSF signal on all sequences, a thin (non-discernible) wall and slight indentation of the vermian surface.

27. Arachnoid cyst motor vehicle accident. no intra axial or extra axial hemorrhage. no calvarial fracture. large extra axial CSF attenuating lesion is seen occupying the left middle cranial fossa splaying the sylvian fissure and displacing the frontal, parietal and temporal lobes.  secondary mass effect is seen in the form of effacement of left cerebral hemispheric sulci , mild midline shift to right,  effaced ipsilateral lateral ventricle.  no transtentorial herniation .  

28. Arachnoid cyst headache Well circumscribed thin walled extra-axial CSF density mass in the right frontal area with remodelling effect on the adjacent bone. The remaining of the study is unremarkable.

29. Retro- cerebellar arachnoid cyst A large right retro- cerebellar extra-axial cyst is seen compressing the right cerebellar hemisphere and elevating the tentorium being insinuated between the occipital lobes. It is seen following CSF signal on all sequences with facilitated diffusion. It is seen measuring 3.2X7.7X6.5 cm along its axial and cranio -caudal dimensions. Annotated image showing the membrane of the arachnoid cyst (red arrows). Remodelling of the skull is also present (blue arrow head).    cystoperitoneal shunt

30. Posterior fossa   arachnoid cysts  can be classified into four subgroups as follow: 1a:  midline inside the 4th ventricle treated by shunting or endoscopic fenestration 1b :  midline outside the 4th ventricle, treated by surgery 2a :  off-midline within the cerebellopontine angle treated by surgery or endoscopic fenestration 2b :  off-midline either retro- cerebellar or intracerebellar treated by surgery

31. Quadrigeminal cistern arachnoid cyst There is a well-circumscribed, rounded lesion with imperceptible walls located at the level of quadrigeminal cistern following CSF signal in all pulse sequences without evidence of soft tissue component. It is exerting mass effect over the third ventricle and aqueduct of sylvius with resultant moderate dilatation of the third and lateral ventricles. 

32. Epidermoid cyst - cerebellopontine angle

33. Mega cisterna magna Large retrocerebellar space that follows CSF signal on all sequences. Normal cerebellar vermis .  Case Discussion Incidental mega cisterna magna. Images at higher levels confimed the presence of a normal posterior fossa and vermis distinguishing it from a  Dandy-Walker malformation .

34. Neuroglial cyst