The anatomical variations of sylvian veins and cisterns.

The anatomical variations of sylvian vein and cistern were investigated during the pterional approach in 750 operative cases with different pathologies. All patients were operated on at the Neurosurgical Department of Ataturk University Medical School, Erzurum, Turkiye. The patients underwent surgery for the lesions necessitating the right or left pterional approach. The findings were recorded during surgical intervention and observed through the operative sketches of the pathologies, the slides, and videotapes of the operations. In our study, we surgically classified the variations of sylvian vein, according to its branching and draining patterns. Type I: The fronto-orbital (frontosylvian), fronto-parietal (parietosylvian) and anterior temporal (temporosylvian) veins drain into one sylvian vein. Type II: Two superficial sylvian veins with separated basal vein draining into the sphenoparietal and Rosenthal's basal vein. Type III: Two superficial sylvian veins draining into the sphenoparietal and the superior petrosal veins. Type IV: Hypoplastic superficial sylvian vein and the deep one. Four types of sylvian vein variations were defined as follows. The type I was seen in 52.8% (n = 396), the type II was found in 19.2% (n = 144), type III was recorded in 18.2% (n = 137), and type IV, or hypoplastic and deep form was discovered in 9.8% (n = 73) of patients. The coursing of sylvian vein was in the temporal side (Temporal Coursing) in 62.4 percent of the cases (n = 469), in the frontal side (Frontal Coursing) in 25 % of the patients (n = 187) and in 9 percent of the cases (n = 67) in the deep localization (Deep Coursing). Only 3.6% of the cases (n = 27) showed Mixed Coursing. The variations of the sylvian cisterns were classified into three types, according to the relationships between the lateral fronto-orbital gyrus and the superior temporal gyrus. In Sylvian type, the frontal and temporal lobes are loosely (Sylvian Type A, wide and large) or tightly (Sylvian Type B, close and narrow) approximated on the surface thereby covering the substance of the sylvian cistern. In Frontal Type, the proximal part of the lateral fronto-orbital gyrus herniated into the temporal lobe. In Temporal Type, the proximal part of the superior temporal gyrus herniated into the lateral fronto-orbital gyrus. The variations of the sylvian cisterns in 750 patients with different pathologies, were as follows: in 47.7% (n = 358) Sylvian type A, in 27.2% percent (n = 204) Sylvian type B, in 16.3% (n = 122) frontal type and in 8.8% (n = 66) temporal type. We concluded that venous perfusion discorder of the brain is the most important factor during the pterional approach. Careful intraoperative assessment and protection of the sylvian vein, which is a surgical pitfall, is an indispensable part of the operation. The recognition of the anatomical variations of the sylvian vein and cistern, and the detailed knowledge of the microvascular relationships and the importance of preservation of this vein at that level, will allow the neurosurgeon, believing in the minimally invasive neurosurgical techniques, to construct a better and safer microdissection plan, to save time, and can prevent postoperative neurological deficits.