- Pterional approach
Superficial dissection strategy for basilar bifurcation aneurysms. Detaching and mobilizing the anterior temporal lobe opens the operative corridor through the carotid-oculomotor triangle.
(A)
Step 1, Splitting the sylvian fissure separates the frontal and temporal lobes;
Step 2, Cutting arachnoid adhesions and granulations along the middle fossa floor frees the inferior temporal lobe;
Step 3, and dividing the temporopolar vein untethers the anterior temporal lobe.
(B)
Step 4, The temporal lobe now mobilizes posterolaterally, opening the pretemporal corridor.
Step 5, Dissection along the cisternal segment of the anterior choroidal artery (AChA) releases the medial temporal lobe.
Step 6, Dissection along the anterior temporal artery (ATA) allows more posterior mobilization of the temporal lobe.
Deep dissection strategy for basilar bifurcation aneurysms.
Step 1, Identifying the PCoA as it originates from the ICA;
Step 2 and 3, Following the PCoA to the P1-P2 junction;
Step 4, Dissecting the P2 segment laterally over the oculomotor nerve to the tentorial edge;
Step 5, Dissecting the inferior surface of the P1 segment medially through Liliequist’s membrane;
Step 6, Identifying the SCA;
Step 7, Securing proximal control on the basilar trunk. An, aneurysm.
Deep dissection strategy for basilar bifurcation aneurysms.
Step 8, Dissecting the ipsilateral P1 segment along its superior surface proximally to the aneurysm neck;
Step 9, Shifting across the basilar apex to identify the contralateral SCA;
Step 10, Identifying the contralateral PCA and distal aneurysm neck;
Step 11, Clearing a pathway across the aneurysm neck for the anterior clip blade;
Step 12, Dissecting perforators across the posterior aneurysm neck for the posterior clip blade.
Visualization of perforators in the blind spot (X) often requires temporary clipping and aneurysm mobilization.
PCP, posterior clinoid process.
Variations in dome projection with basilar bifurcation aneurysms.
(A) A superiorly projecting aneurysm creates a blind spot that hides the thalamoperforators (Perf.) behind the distal neck.
(B) An anteriorly projecting aneurysm creates a blind spot that hides the contralateral PCA and SCA.
(C) A posteriorly projecting aneurysm creates a blind spot that hides the thalamoperforators originating from the posterior base of the
aneurysm.
(D) High-riding basilar bifurcation aneurysms ascend out of the carotid-oculomotor window, and the ICA can create an additional blind spot.
(E) Low-riding basilar bifurcation aneurysms descend out of the carotidoculomotor window and are obstructed by the posterior
clinoid process.
Anatomic triangles providing access to the basilar bifurcation:
1, Optic-carotid triangle;
2, Carotid-oculomotor triangle;
3, Supracarotid triangle.
The carotid-oculomotor triangle is the one used most commonly for basilar bifurcation aneurysms. Tent., tentorium
See Kim 2015
Effect of the removal of the posterior clinoid process (PCP) on the opticocarotid window (OCW) and carotidoculomotor (COW) in the case of a low-lying basilar apex. The basilar apex is located 3.2 mm below the PCP. The sylvian fissure is widely opened, and the internal carotid artery (ICA) is retracted medially or laterally. A, the OCW after step 2 (right side). Due to a prominent PCP and a low-lying basilar apex, the basilar trunk is not visible, and the temporary occlusion of the BA is not feasible. B, the OCW after step 3 (right side). After removal of the PCP, the distance from the apex of basilar artery (BA) to the proximal-most point of visualization of the BA is 5.3 mm, and the surgical area for temporary clip application is 28.4 mm2. C, the COW after step 2 (left side). Because of a prominent PCP, dorsum sellae, and a low-lying basilar apex, temporary occlusion of the BA is not feasible. D, the COW after step 3 (left side). After removal of the PCP and dorsum sellae, the distance from the apex of BA to proximal-most point of visualization of the BA is 6.6 mm and the surgical area for temporary occlusion increased from 0 to 39.0 mm2. Apex, apex of basilar artery; AChA, anterior choroidal artery; SCA, ipsilateral superior cerebellar artery; SCA*, contralateral superior cerebellar artery; PCoA, posterior communicating artery; P1, ipsilateral P1 segment; P1*, contralateral P1 segment of the posterior cerebral artery; P2, ipsilateral P2 segment of PCA; M1, M1 segment of middle cerebral artery; A1, A1 segment of the anterior cerebral artery; ON, optic nerve; III, oculomotor nerve; step 2, drilling out the anterior clinoid process intradurally and cutting the distal dural ring and mobilization of the ICA; step 3, drilling out the PCP and dorsum sellae.
Effect of division of the posterior communicating artery (PCoA) on the opticocarotid window (OCW) according to the height of the basilar apex (A-D, the OCW through steps 3 and 4, right side). A, B, the basilar apex is located 4.3 mm above the posterior clinoid process (PCP). C, D, the basilar apex is located 12.2 mm above the PCP. A, step 3. B, step 4. C, step 3.D, step 4. After step 4, the superior and total area of the OCW still remained the same with step 3, regardless of basilar apex height. Via the OCW, the area above basilar apex (area for permanent clip application) in C and D (high-lying basilar apex) is very tight. The mean area for permanent clip application through the OCWwith high-lying apex seemed smaller than with a low-lying apex after step 4. However, no significant difference was found. A1, A1 segment of the anterior cerebral artery; Apex, apex of basilar artery; BA, basilar artery; ICA, internal carotid artery; M1, M1 segment of middle cerebral artery; ON, optic nerve; P1, ipsilateral P1 segment; P1*, contralateral P1 segment of the posterior cerebral artery.
The effect of dividing the posterior communicating artery (PCoA) on the carotid-oculomotor window (COW) according to height of the basilar apex (A-D; the COW through steps 3 and 4, right side). A, B, the basilar apex (Apex) is located 4.3 mm above the posterior clinoid process (PCP). C,D, the basilar apex is located 12.2 mm above the PCP. A, step 3. B, step 4. C, step 3. D, step 4. Division of the PCoA significantly increased the area for permanent clip application and the total area through the COW, regardless of basilar apex height.C,D, through the COW, the area above the basilar apex (area for permanent clip application) in the high-lying basilar apex is very tight. The mean area for permanent clip application through the COW of a high-lying apex seemed smaller than a low-lying apex. However, no significant difference was found. AChA, anterior choroidal artery; BA, basilar artery; ICA, internal carotid artery; III, cranial nerve III; P1, ipsilateral P1 segment; P1*, contralateral P1 segment; P2, ipsilateral P2 segment; ON, optic nerve; SCA, ipsilateral superior cerebellar artery; step 3, drilling out the PCP and dorsum sellae; step 4, dividing the PCoA at the posterior third of the PCoA .
The effect of dividing the posterior communicating artery (PCoA), on the opticocarotid window (OCW), and carotid-oculomotor window (COW) in the case of a short and adult-type PCoA (left-side approach). The basilar apex is located 13.3 mm below the posterior clinoid process (PCA). A, the OCW after step 3. The PCoA blocked the view of the apex. B, the OCW after step 4. The apex is still not visible through the OCW because the perforators from the PCoA tether the internal carotid artery (ICA), preventing further lateral retraction even after the division of the PCoA.C, the COW after step 3. The PCoA tethers the ICA, and the apex is not visible.D, the COW after step 4. The ICA was released from its attachment site on the PCA, and the ICA along with the perforators from the PCoA all were moved together away from the basilar apex. A1, A1 segment; Apex, apex of basilar artery; AChA, anterior choroidal artery; BA, basilar artery; III, cranial nerve III; M1, M1 segment; ON, optic nerve; P1, ipsilateral P1 segment; P1*, contralateral P1 segment; P2, ipsilateral P2 segment; P2*, contralateral P1 segment; PCoA, posterior communicating artery; SCA*, contralateral superior cerebellar artery; step 3, drilling out the PCP and dorsum sellae; step 4, dividing the PCoA at the posterior third of the PCoA. Blue arrow, attach site of the PCoA on the PCA.
The effect of dividing the posterior communicating artery (PCoA) on the opticocarotid window (OCW) and carotid-oculomotor window (COW) in the case of a long and hypoplastic posterior communicating artery (PCoA). In the case of a long hypoplastic PCoA, the division of the PCoA did not increase the surgical area through either window. A long hypoplastic PCoA can be mobilized and retracted out of the way of dissection without being sacrificed (B, E). A, B, the OCW after step 3. C, the OCW after step 4. D, E, the COW after step 3. F, the COW after step 4. AChA, anterior choroidal artery; A1, A1 segment; Apex, apex of basilar artery; BA, basilar artery; ICA, internal carotid artery; III, cranial nerve III; ON, optic nerve; P1, ipsilateral P1 segment; P1*, contralateral P1 segment; P2, ipsilateral P2 segment; SCA, ipsilateral superior cerebellar artery; step 3, drilling out the PCP and dorsum sellae; step 4, dividing the PCoA at the posterior third of the PCoA. Blue arrow, attach site of the PCoA on the PCA.
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