Selecting the optimal keyhole approach for internal carotid and middle cerebral artery aneurysms. Anatomical comparison of transorbital, lateral supraorbital and minipterional routes with clinical implications

Abstract Purpose Among the keyhole approaches for the treatment of anterior circulation aneurysms, the minipterional (MPT) and lateral supraorbital (LSO) mini-craniotomies have gained great acceptance. With the recent introduction of the transorbital (TO) route to the Silvian fissure and carotid cistern, an objective analysis is required to stablish general indications and limits to each approach. Methods Four heads (8 sides) were used for each of the three approaches (TO, LSO, MPT). All specimens underwent a basal CT scan for neuronavigation. Procedures were performed simulating a real surgical scenario, exposing four vascular targets: posterior communicating artery (PCom), internal carotid bifurcation (ICA), M1 segment and bifurcation of the middle cerebral artery (MCA). Surgical freedom (SF) and working angles were calculated at the four vascular targets, and mean differences were compared with Kruskal–Wallis. Transferability of data are demonstrated with three illustrative cases. Results The ICA segments C6-C7, PCom and M1 segment and MCA bifurcation could be exposed ipsilaterally in all specimens and for all three approaches. With the PCom as a target, mean area of SF achieved was 36.19 (27.66) cm 2 for TO, 71.35 (21.04)cm 2 for LSO, and 101.59 (42.34)cm 2 for MPT (p = 0.013). At the ICA bifurcation, the LSO offered the maximal SF area (85.34 IQR38.42 cm 2 ) (p = 0.025), with ventral and horizontal angles also favouring the LSO. At the M1, there were no significant differences between the approaches. Notably, the TO approach provides its maximal SF and degree of instrument angulation at the M1 (68.02 IQR35.04 cm 2 ). Manoeuvrability at the MCA bifurcation was maximal with the MTP (90.99 IQR26.88 cm 2 ), although the differences did not reach statistical significance compared to LSO (72.02 IQR19.13 cm 2 ) and TO (42.38 IQR3.37 cm 2 ) (p = 0.132). Three clinical cases of unruptured MCA and ICA aneurysms are detailed. Conclusions Our data supports the addition of a new ventral route – the TO approach – to the already available keyhole routed to the anterior circulation (MTP and LSO). Manoeuvrability analysis contemplates independently four major vascular targets, providing more detailed data to help select the most appropriate approach for each individual case.