Choroidal fissure cyst (CFC) is a rare embryological entity presenting as cerebrospinal fluid (CSF) containing cysts at the level of the choroidal fissure. The literature is lacking articles discussing this topic, with only case few reports and series.1–3 There are several theories exist to explain the mechanism of primary choroidal cysts development: 1) as a result of aberrant splitting and duplication in the arachnoid membrane as proposed by Starkman et al.2 and Krawchenko and Collins,4 2) in response to temporal lobe agenesis, resulting in forming a cyst in the subarachnoid space,5 and 3) from invagination of the vascular mesenchyme of the primitive choroid plexus into adjacent brain picked up an outer covering of glial tissue.6
Computed tomography (CT) and magnetic resonance imaging (MRI) are used to differentiate between the CFC and other differential diagnoses of cysts located at the choroidal fissures including cystic neoplasm, dermoid/epidermoid cysts, and enlargement of the choroidal fissure due to focal temporal lobe atrophy.1 CT scans show a well-delineated homogeneous low-density mass with attenuation characteristics similar to CSF without calcification or contrast enhancement. MRI signal characteristics are similar to CSF on all sequences. The cyst walls are thin and contrast enhancement, surrounding edema, and gliosis are absent.7 The coronal images are better to identify the relation between the cyst and the choroidal fissure.1 The final diagnosis can only be made by histopathological examination. The cysts are usually small asymptomatic and discovered incidentally. Very rarely, they may cause seizures due to the mass effect on the temporal lobe.8
A literature review of this topic was conducted by searching human, English-language publications in MED-LINE (PubMed and Ovid), Google Scholar, and Cochrane Library from January 1, 1950 to June 9, 2020.
Table 1 shows the total cases of CFC mentioned in the literature. The current review showed 20 cases reported in the literature (Table 1). The right side was more common (60%) and seizure was the main presenting symptom in 13 cases (65%). The type of treatment was mentioned in 11 cases and all were managed conservatively. However, no information was available in the remaining nine cases. In the Sherman series,1 26 patients had cysts in or near the choroidal fissure of the temporal lobe, and it was bilateral in two patients. The report described five patients with a seizure disorder, none of them electroencephalographically correlated to the cyst location as the epileptogenic cortex usually was not adjacent to the patient’s cyst.1
Arroyo and Santamaria9 describe a series of 17 patients with epilepsy and an arachnoid cyst. Of which, nine were having CFCs. The authors suggested that these cysts are often incidental findings and do not necessarily reflect the location of the seizure focus. Millichap10 describes three patients with a temporal arachnoid cyst, one of them being a CFC, presenting with attention deficit hyperactivity disorder and headache. The author recommended neuropsychological tests for associated attention and learning deficits which might be observed in cases with CFCs.
CFCs are embryological lesions that are rarely described in the literature due to their benign nature and tendency to be asymptomatic. The CFCs do not always reflect the location of the seizure focus. In all the cases reported in the literature, surgical treatment was not considered. Follow-up with regular imaging will is suggested. However, the frequency of these surveillance scans and when follow-up can be stopped is still unknown.
