Sylvian fissure arachnoid cyst
Arachnoid cysts situated in the middle cranial fossa constitute the largest group of this type of lesion.
The Galassi classification of middle cranial fossa arachnoid cysts is used to classify arachnoid cysts in the middle cranial fossa, which account for 50-60% of all arachnoid cysts.
Galassi et al published this classification in 1982, and at the time of writing (November 2016) it remains the most widely used system for these lesions.
It is a simple system, using the size and degree of displacement of adjacent brain to divide cysts three types. The size also correlates with the ease with which the cyst communicates with the subarachnoid space as discerned on CT cisternography or phase contrast MRI.
type I small, spindle-shaped limited to the anterior portion of the middle cranial fossa, below the spenoid ridge free communication of subarachnoid space
type II superior extent along sylvian fissure displacement of the temporal lobe slow communication with subarachnoid space
type III large, fills the whole middle cranial fossa displacement of not only the temporal lobe but also the frontal and parietal lobes often results in midline shift little communication with subarachnoid space
Intracranial sylvian arachnoid cysts are often asymptomatic lesions.
(a) Axial CT scan showing a left sylvian fissure arachnoid cyst. (b) Complete resolution after excision and marsupialization.
The option of the mere clinical observation was chosen by the majority of surgeons in case of asymptomatic clinical discovery. On the other hand, a constantly high percentage of participants suggested direct surgical treatment based on clinical manifestations or as a preventive measure justified by the risk of spontaneous or traumatic intracranial bleeding. The only diagnostic investigation result which significantly influenced the surgical indication was a localizing electroencephalography, if the child presented with seizures. The result is that in most cases the surgical indication was based on a specific clinical manifestations and laboratory data. Craniotomy and arachnoid cyst marsupialization represented the preferred surgical option (66.6%), 28.8% of the participants suggesting pure or assisted endoscopic cyst marsupialization as primary surgical procedure. Cyst shunting was suggested by only three centers 2).
A study demonstrated efficacy in a predominantly endoscopically treated patient cohort with Sylvian fissure arachnoid cysts, as indicated by improvement of clinical symptoms and diminished radiological SAC volume after treatment 3)
it sometimes leads to subdural or intracystic hemorrhage without major trauma. The reason of easy bleeding of the AC is not fully understood.
One of the rare complications after rapid decompression of the arachnoid cysts is haemorrhage in the surrounding brain as well as in remote areas.
Long-standing asymptomatic sylvian arachnoid cysts may suddenly produce severe unilateral visual deficits if the cyst erodes the lateral orbital wall. These deficits may rapidly revert to normal if surgical action is not delayed. If surveillance MRIs of sylvian arachnoid cysts show a narrowing of the conus diameter compared to the contralateral side, a yearly ophthalmological surveillance examination seems to be warranted in else wise asymptomatic patients 4).
A retrospective review of the database of operative procedures revealed 24 procedures (20 endoscopic and 4 microsurgical procedures) to fenestrate a Sylvian fissure arachnoid cyst (SAC) at university hospitals in Berlin, Germany and Tokyo, Japan.
With the applied technique, a reduction of SAC volume of more than 10% was achieved in 83.3% of all patients. The median volume of SACs (n = 24) was significantly reduced from 83.5 mL (range 21-509 mL) preoperatively to 45.5 mL (range 8.4-261 mL; P < 0.01) after 3.5 months and to 29.0 mL (range 0-266 mL; P < 0.01) after 15 months. In children (n = 8) with a ruptured SAC the combined extraaxial volume of a SAC and accompanying hygroma/hematoma was reduced from 166 mL (range 111-291 mL) before surgery to 127 mL (range 87-329 mL) after 2 months and to 77 mL (range 25-140 mL; P < 0.05) after 11 months. Acute clinical symptoms were generally resolved postoperatively; headaches were resolved or improved in 75%. A significant association of resolution or improvement of headaches and volume reduction was demonstrated.
The study demonstrated efficacy in a predominantly endoscopically treated patient cohort with Sylvian fissure arachnoid cysts, as indicated by improvement of clinical symptoms and diminished radiological SAC volume after treatment 5).
A case of multiple remote-site intra-parenchymal haemorrhage as a rare complication after surgical decompression of a sylvian fissure arachnoid cyst 6).
Lohani et al., present the case of an 11-year-old boy who presented after a week of progressive and severe back pain radiating to the back of his thighs. Imaging revealed a spinal subdural blood collection at the L4-S1 level. This finding prompted further cephalad imaging of the spine and the brain, which revealed a sylvian fissure arachnoid cyst with intracystic hemorrhage and frontoparietal subdural hematoma. The child did not have headache at this time, although he had experienced chronic headaches since the age of 4 years. He was treated with a course of oral steroids, which immediately relieved his back and leg pain. Subsequent imaging showed resolution of the cranial and spinal subdural blood collections and diminished size of the arachnoid cyst. No surgical treatment was necessary 7).
Upadhyaya et al. report a case of a sylvian cistern arachnoid cyst presenting with precocious puberty in a 3-year-old girl. The child recovered following a cystoperitoneal shunt. The mass effect of the arachnoid cyst upon the hypothalamus was, at least in part, responsible for the development of precocious puberty. To the best of the knowledge, this is the 1st case of a sylvian cistern arachnoid cyst presenting with precocious puberty. The role of surgical decompression of the cyst is also discussed 8).
Prokopienko et al., report the case of a 36-year-old woman with a Sylvian fissure arachnoid cyst, which diminished after head trauma and minor hemorrhage into the cyst. They discuss the relationship between the cyst volume reduction and the head trauma to determine the main mechanism of this self-healing process 9).
Intraparenchymal hemorrhage after surgical decompression of a Sylvian fissure arachnoid cyst 10).
A case of brain stem hemorrhage after decompression of a sylvian fissure arachnoid cyst has been reported 11).