Spontaneous Disappearance of an Arachnoid Cyst after appearance of chronic subdural hematoma

*M.Hammoud, F.Lakhdar, M.Benzagmout, K.Chakour, M.F Chaoui

Department of Neurosurgery, Hassan II University Hospital of Fez, Morocco University Sidi Mohammed Ben Abdellah, Fez, Morocco

*Corresponding author

*M.Hammoud, Department of Neurosurgery, Hassan II University Hospital of Fez, Morocco University Sidi Mohammed Ben Abdellah, Fez, Morocco.
E-mail: marouane.hammoud@gmail.com


Background: Arachnoid cysts are benign extra axial lesions, most commonly located in the fronto temporal region and account for 1% of all intracranial masses. They may remain stable or they may grow in size over time. Reports of spontaneous disappearance of arachnoid cysts are rare.

Case Report: We report the case of a 1-year-old boy with a middle fossa arachnoid cyst revealed by convulsive seizures, managed with anti epileptic drugs, 13 months later, the patient had one seizure episode, the cranial computed tomography Scan showed nearly total disappearance of the arachnoid cyst and the appearance of subdural hematoma. No surgical intervention was performed. Follow-up CT scans 1 month after admission, showed total disappearance of both the arachnoid cyst and the subdural hematoma.


Arachnoid Cyst, Subdural hematoma, Spontaneous Resolution


Arachnoid cysts are rare benign congenital extra axial lesions, which consist of collection of cerebrospinal fluid (CSF) surrounded by normal arachnoid membrane.

They account for approximately 1% of all intracranial space-occupying lesions, with a higher prevalence in the first 2 decades of life [1].

Most arachnoid cysts are quiescent and remain asymptomatic throughout life. 
They are incidentally detected on CT or magnetic resonance images [2]. 
The cyst may progress, stabilize, or spontaneously regress [3,4].

Spontaneous regression of an AC has been rarely reported in the literature [5,6].

In our knowledge, this is the second reported case of spontaneous disappearance of cerebral arachnoid cyst in less than 2 year [7].

Case report

A 1-year-old boy was admitted to pediatric emergency department for two episodes of non-febrile generalized seizure. On clinical exam, there was no focal neurological abnormality, cranial nerve deficit or papilledema. His head circumference was normal.

Brain magnetic resonance MR imaging showed a well defined, no enhancing, extra-axial cystic lesion in the right frontotemporal region, between the tabula interna and the insula. The lesion is isointense to CSF on T1 and T2 weighted images (Figure 1). This fluid collection suppresses completely with FLAIR and shows no restriction on DWI. The diagnosis of a right frontotemporal arachnoid cyst was made.

We decided not to operate the patient; he was putted under antiepileptic drug,

At 2-months follow-up, the patient was doing well and was seizure-free.

fig 1 2

Figure 1: Brain MRI at the age 2 years showing a right sylvian cystic lesion isointense to CSF on T1 and T2 weighted images.

13months later, the patient was presented with another seizure episode; there was no cranial trauma. The neurological examination was unremarkable.

Unexpectedly, the brain CT scan showed a subtotal resolution of the arachnoid cyst with a subdural hematoma on the same side (Figure 2),

We decided to observe the patient without surgical intervention.

fig 2 2

Figure 2: Cranial CT scans performed after 13 months showing subtotal resolution of the arachnoid cyst with appearance of subdural hematoma on the same side.

At 1-month follow-up, the CT scan control showed total disappearance of both the arachnoid cyst and the subdural hematoma (Figure 3).

fig 3

Figure 3: Follow-up CT scans performed after 14 months showing complete disappearance of the arachnoid cyst and SDH.


First described by Bright in 1831 [8]. ACs are benign cystic lesions, which consist of CSF collections between the two layers of arachnoid membrane, by definition three criteria are required for a lesion to be considered an AC: 1/ it must be enveloped by an arachnoid membrane, 2/ it must contain arachnoid mater cells, and 3/ it must contain CSF [9].

They can be congenital or acquired after surgical trauma, infection, or hemorrhage [10].

In most cases, ACs are asymptomatic, the diagnosis is an incidental finding. When they are symptomatic, they are resulting of the direct compression of surrounding structures, ACs are relatively rare. The reported incidence accounts for only 1% of intracranial space- occupying lesions [11].

On CT, ACs manifest as extra-axial cysts with the density of CSF, it does not enhance after injection. MRI signals are similar to CSF in T1- and T2-weighted imaging with no enhancement on gadolinium.

Diffusion-weighted MRI has proved to be very useful for differential diagnosis that includes other cystic lesions [12].

Arachnoid cysts may remain stable or they may grow in size over time, in rare cases ACs may resolve spontaneously [7]. AC disappearance is a rare phenomenon that can occur spontaneously or after an inciting event.

The mechanism of spontaneous disappearance of ACs has not been described in the literature. Probably Communication between an AC and the subarachnoid space may be direct transport through the cyst wall or it may be a valve-like mechanism [13].

Although, the cyst wall rupture and CSF flow perturbation theories seem to be the most applicable pathophysiological mechanisms in triggered AC resolution(18).

Rupture of arachnoid cyst associated to subdural or intracystic effusion or bleeding is a rare complication. It occurs mostly after a head injury [14].

In this case, there was no history of head trauma, the cyst resolved spontaneously with the appearance of a subdural hematoma SDH. In the literature, there are only 11 cases reported in the literature of spontaneous SDH complicating an arachnoid cyst [15,16].

The management modality of asymptomatic ACs is not clear. However, surgical treatment is suitable for large or symptomatic ACs [17].

SDH associated with ACs spontaneously or due to traumas should be treated in an individual-based manner that is specific to each case, either conservatively or surgically [17,18].

In our case report, based on the clinical assessment no intervention was required.


The present case and the few reported cases of spontaneous disappearance of ACs suggest a more conservative approach in patients without asymptomatic ACs. Thus, we report highlight the interest of regular follow up of patients with known ACs.


  1. Al-Holou WN., et al. “Prevalence and natural history of arachnoid cysts in adults: Clinical article”. Journal of Neurosurgery 118.2 (2013): 222-231.
  2. Seizeur R., et al. “Spontaneous resolution of arachnoid cysts: review and features of an unusual case”. Acta Neurochirurgica 149.1 (2007): 75-78.
  3. Dodd RL., et al. “Spontaneous Resolution of a Prepontine Arachnoid Cyst”. Pediatric Neurosurgery 37.3 (2002): 152-157.
  4. Terao T., et al. “[A case of spontaneous rupture of a suprasellar cystic mass]”. No Shinkei Geka 29.8 (2001): 755-758.
  5. Weber R., et al. “Spontaneous regression of a temporal arachnoid cyst”. Child’s Nervous System. CHILD NERV SYST, Child”s Nervous System: ChNS: Official Journal of the International Society for Pediatric Neurosurgery 7.7 (1991): 414-415.
  6. Pandey P., et al. “Spontaneous decompression of a posterior fossa arachnoid cyst: a case report”. Pediatric Neurosurgery 35.3 (2001): 162-163.
  7. Adilay U., et al. “Spontaneous Resolution of a Sylvian Arachnoid Cyst in a Child: A Case Report”. Pediatric Neurosurgery 52.5 (2017): 343-345.
  8. Bright R. “Reports of medical cases selected with a view of illustrating the symptoms and cure of diseases by a reference to morbid anatomy”. Brain Disorders Nervous System (1931).
  9. Cohen MA., et al. “Long-term Follow-up of a Multiloculated Arachnoid Cyst of the Middle Cranial Fossa”. Ear, Nose and Throat Journal 86.6 (2007): 338-341.
  10. Jean WC., et al. “Cervical arachnoid cysts after craniocervical decompression for Chiari II malformations: report of three cases”. Neu- rosurgery 43.4 (1998): 941-944.
  11. Gosalakkal JA. “Intracranial arachnoid cysts in children: a review of pathogenesis, clinical features, and management”. Pediatric Neu- rology 26.2 (2002): 93-98.
  12. Tsuruda JS., et al. “Diffusion-weighted MR imaging of the brain: value of differentiating between extraaxial cysts and epidermoid tumors”. American Journal of Neuroradiology 11.5 (1990): 925-931.
  13. Go KG., et al. “Arachnoid cysts of the sylvian fissure. Evidence of fluid secretion”. Journal of Neurosurgery 60.4 (1984): 803-813.
  14. Wester K and Helland CA. “How often do chronic extra-cerebral haematomas occur in patients with intracranial arachnoid cysts?” Journal of Neurology, Neurosurgery, and Psychiatry 79.1 (2008): 72-75.
  15. Burke MP. et al. “Spontaneous acute subdural hematoma complicating arachnoid cyst”. The American Journal of Forensic Medicine and Pathology 31.4 (2010): 382-384
  16. Hall A., et al. “Spontaneous subdural haemorrhage from an arachnoid cyst: a case report and literature review”. British Journal of Neurosurgery 31.5 (2017): 607-610.
  17. Cincu R., et al. “Intracranial arachnoid cysts: Current concepts and treatment alternatives”. Clinical Neurology and Neurosurgery 109.10 (2007): 837-843.
  18. Yilmaz, C., Cetinalp, E., Caner, H. et al. Dissapearance of arachnoid cyst after rupturing into subdural space. Acta Neurochir (Wien) 149, 731 (2007).