Anterior Cerebral Artery Aneurysm: Ruptured Distal Azygos Anterior Cerebral Artery Aneurysm; Interhemispheric Approach,Positioning of Head, Rationale Interhemispheric Approach, Positioning of Head, Rationale for Open Surgery
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A 69-year-old male presented with a sudden onset severe headache after an episode of heavy coughing one morning. He was a heavy smoker and his medical history included chronic obstructive pulmonary disease (COPD). He was taken to the nearest hospital and underwent CT-scanning because of persistent headache. The CT revealed subarachnoid hemorrhage (SAH) in the anterior interhemispheric fissure, suggestive of an aneurysmal etiology. His clinical condition was graded as Hunt and Hess II. Emergent CT-angiography revealed multiple cerebral aneurysms including one arising from the distal anterior cerebral artery (DACA). A V-shaped aneurysm of the left anterior A3 segment (pericallosal artery) measuring 4 × 3 × 3 mm was identified as the most likely rupture site. Further aneurysms included an incidental 2 × 2 mm aneurysm of the left middle cerebral artery (MCA), a 3 × 2 mm left posterior communicating artery (PcomA) aneurysm and a 5 × 5 mm aneurysm of the basilar artery. DSA demonstrated a DACA aneurysm at the bifurcation of the callosomarginal artery (A3 segment of the distal ACA) on a single inferior A3 to A2 trunk, with a bilobar, V-shaped configuration. The aneurysm was wide-necked and it was not clear whether the associated callosomarginal artery was running adjacent to, or efferent from, this aneurysm. The decision to recommend emergent microsurgical clipping was based on an interdisciplinary risk-benefit analysis. Microsurgery was performed via a focused interhemispheric approach with aneurysm exclusion and vessel wall reconstruction aided by temporary clipping of the proximal A3 segment, with the patient’s head in a neutral position. The postoperative course was complicated by delayed weaning from the ventilator due to longstanding nicotine abuse, marked COPD and pulmonary emphysema. Forty-one days after the initial presentation, the patient was discharged without neurological deficit. Management aspects of DACA aneurysms including their characteristics and challenges are the main topic of this chapter.
KeywordsAnterior cerebral artery Azygos anterior cerebral artery Clip reconstruction Trajectory-focused interhemispheric approach Intraoperative ICG angiography Temporary clipping
A 69-year-old male smoker with known COPD and emphysema suffered a sudden onset of severe headache after an episode of heavy coughing one morning. Due to a persisting severe headache, he was brought to the nearest hospital and underwent a CT examination. His clinical condition was rated as Hunt and Hess II.
Endovascular reconstruction of the azygos ACA bifurcation with exclusion of the ruptured aneurysm from circulation did not appear feasible. It was decided, therefore, to adopt an open microsurgical approach with clip reconstruction of the arterial wall at the aneurysm neck, to exclude the aneurysm while preserving the callosomarginal artery.
Procedure, 12.01.2019: Focused open microsurgical approach via a mini-craniotomy with clip exclusion of the ruptured azygos anterior cerebral artery aneurysm. Operative challenges included the wide aneurysm neck, the origin of the pericallosal artery from the aneurysm neck and additional aneurysmal changes of the A3 segment.
Anesthesia: general anesthesia, TIVA
Technical equipment: Zeiss Pentero operating microscope, indocyanine green angiography (ICG)
Course of treatment: The patient was positioned supine, anesthetized, intubated, and ventilated. The head was clamped in a neutral position in order to facilitate exposure of the aneurysm using a perpendicular trajectory. Orientation landmarks were taken from the sagittal imaging in the midline with respect to the genu of the corpus callosum. The landmarks for craniotomy are measured 4 and 6 cm from the nasion. A horizontal incision mark was drawn, crossing the midline. After draping and creation of the skin incision, the frontal flap was retracted anteriorly with tissue hooks to expose the calvarium. A burr-hole was created which straddled the superior sagittal sinus on the left, and this was followed by a mini-craniotomy crossing the sagittal sinus. Due to the raised intracranial pressure, a mannitol-induced osmodiuresis was initiated. After the left side of the interhemispheric fissure was opened with a retractorless technique, aiming for the genu of the corpus callosum, blood clot was removed. The A3 segment of the ACA was followed from distal to proximal in order to sequentially expose the superior, anterior, and inferior A3 segments. After identification of the aneurysm, the patient was prepared for temporary clipping of the azygos ACA proximal to the aneurysm by maximal preoxygenation and thiopentone narcosis. The azygos ACA was then temporarily clipped in order to depressurize the aneurysm complex and enable a safe dissection and exposure of aneurysm and parent artery as well as the efferent vessels from the clot and brain tissue. With temporary proximal azygos ACA clipping, the aneurysm turgor was diminished, and it became possible to cautiously place a 7 mm pilot clip anterolaterally across the neck of the larger part of the aneurysm complex. Due to vessel-wall calcifications, a small triangular neck remnant was left behind by the pilot clip and was excluded with an additional 5 mm straight mini clip. Eventually, the vessel wall was reconstructed with maintained perfusion of the dependent pericallosal and callosomarginal branches. An additional 5 mm slightly curved clip was applied to exclude a second A3 aneurysmal limb anteromedial to the larger, ruptured aneurysm complex. After 5 min, the temporary proximal azygos ACA clip was removed and ICG demonstrated minimal residual perfusion of the larger double-clipped aneurysm. The small straight 5 mm clip was therefore carefully reopened and advanced slightly in a caudal direction under direct ICG view. This maneuver resulted in complete exclusion of the aneurysm from the circulation. The operative site was rinsed with Ringer’s solution, followed by dural closure, reinsertion, and fixation of the bone flap with miniplates and skin closure and unclamping of the patient.
After surgery, weaning from the ventilator was protracted due to COPD and pulmonary emphysema secondary to longstanding nicotine abuse. Fourteen days post-surgery, the patient was successfully extubated and after a further 9 days, he was discharged from the ICU. The patient left the hospital 41 days after the initial presentation without neurological deficit. Treatment of the remaining incidental aneurysms is scheduled, with priority being given to the basilar artery aneurysm, which is planned for treatment with WEB device placement.
The postoperative NCCT and CTA demonstrated a “clean” surgical field with no untoward sequelae (e.g., cerebral contusion or signs of ischemia). At the site of the vessel wall reconstruction with the two clips, the callosomarginal artery was shown to course around the clip tips.
Our patient presented with SAH centered on the anterior interhemispheric fissure. The CTA revealed four intracranial aneurysms. DACA aneurysms make up 6% of all intracranial aneurysms (Lehečka et al. 2008). Patients with DACA aneurysms often have multiple aneurysms, in some series over 50% (Steven et al. 2007). Two V-shaped ACA aneurysms were located at the bifurcation of the azygos ACA into the pericallosal arteries, adjacent to the genu of the corpus callosum: the ruptured one was located anteriorly and laterally with diameters of 4 × 3 × 3 mm, and the second was 2 mm in diameter and located more anteromedially at the bifurcation into the pericallosal arteries. As an anatomical variant there was an azygos A2 segment proximal to both efferent A3 segments, the pericallosal arteries. The ACA aneurysms can be classified into distal ACA (DACA) and proximal, the former are differentiated into inferior, anterior, and dorsal according to their location in relation to the genu of the corpus callosum (Lehečka 2009). Different nomenclatures are in use. Lehečka et al. (2008) from the Helsinki group consider that the A2 becomes the A3 at the junction of rostrum and the genu of corpus callosum. As such the segment directly below the pericallosal artery and CMA branch would still be termed “inferior A3.” The patient described above had a further three aneurysms: an incidental 2 × 2 mm aneurysm of the left MCA, a 5 × 5 mm of the basilar artery, and a 3 × 2 mm of the left PcomA.
ACA aneurysms are known to have a higher rupture risk (Backes et al. 2015; Greving et al. 2014) and to rupture at smaller size than other intracranial aneurysms. Despite the patient’s four aneurysms, the initial NCCT unequivocally suggested the DACA aneurysm as the source of bleeding. To avoid the high risk of re-rupture within the first 6–12 h (Germans et al. 2014), urgent treatment was required and the surgery was commenced 14 h after the onset of headache. The case also demonstrates that even at small size, aneurysms can have complex configurations with broad necks and emanating branches. This is particularly the case with DACA aneurysms and as such, the risks of DACA aneurysm treatment include the occlusion of such branches (e.g., the CMA).
Following emergent admission to the intensive care unit (ICU), immediate catheter angiography was performed to plan further treatment, after the patient was anaesthetized and intubated. He received an intraventricular CSF drain for intracranial pressure (ICP) monitoring and management in the ICU prior to angiography. The DSA showed an azygos ACA with an aneurysm at the bifurcation of the single A2 segment into the two pericallosal arteries and the left callosomarginal artery, an anterior A3 DACA aneurysm. The aneurysm was wide-necked and there was a potential origin of the CMA at the dome of the ruptured aneurysm limb and a second more medial limb.
As a result of the discussion with the neuro-interventional team, the risk-benefit ratio was considered to be in favor of open microsurgery, predominantly due to the combination of the broad aneurysm neck, uncertain CMA origin and an overall aneurysmal change of the A2/A3 transition. Successful management of azygos ACA aneurysms has been reported (Saponiero et al. 2008; Sarikaya et al. 2008). In our patient, however, coil occlusion alone would not have been feasible and any stent-assisted procedure would have been associated with significant procedural risks. Therefore, the decision for emergent microsurgical clipping was made.
The surgery was performed with the patient supine and with a neutral head position, to help orientation. For a direct and focused approach, it is of utmost importance to have a clear impression of the anticipated aneurysm location in the sagittal plane, to enable the interhemispheric trajectory to the aneurysm to be as perpendicular as possible. Otherwise the surgeon will have to “search” along the corpus callosum, which increases the risk of bleeding from the small fragile vessels along the interhemispheric corridor. In order to optimize the trajectory, it is helpful to identify the position of the aneurysm complex in relation to the genu of the corpus callosum and proper inclination of the head is important to achieve this. In the vast majority of cases, the head should be in a neutral sagittal position, and only for quite inferior DACA aneurysms is slight retroversion of the head necessary (Kretschmer and Schmidt 2017). Stereotactic navigation can help in this regard. However, it is also possible to turn the head into a lateral position (90°) for interhemispheric approaches with the “pathology-side” down. This increases the preparation corridor by lowering the downward hemisphere via “gravity-retraction.” However, orientation in the sagittal plane is then slightly more challenging.
Due to the known fragility of the aneurysm wall in DACA aneurysms, the use of flow reduction through temporary clipping of the proximal A2 is helpful to avoid intraprocedural rupture prior to full aneurysm exposure. Temporary clipping of the proximal ACA depressurizes the aneurysm and allows for faster and better controlled exposure of the entire aneurysm including the neck and the efferent branches. Thus, access to the proximal vessels should be considered when planning both the craniotomy and the approach trajectory.
In our case, a burr-hole was created, straddling the superior sagittal sinus (SSS) on the left followed by a mini-craniotomy of 2 × 4 cm which crossed the sagittal sinus with the long side oriented in the sagittal plane. With the crossing of the SSS, the dura can be opened at the edge of the SSS allowing for a broader interhemispheric fissure access without any overhanging bone to limit the surgeon’s view. Then the left interhemispheric fissure can be comfortably opened with a retractorless technique to avoid retractor-related injuries and to improve both the view and the degree of manual freedom (Spetzler and Sanai 2012).
In summary, precise trajectory planning via meticulous patient positioning either using gravity-retraction and/or intraoperative CSF drainage allows for a focused and minimal invasive, tissue-sparing, interhemispheric, and possibly retractorless approach. Proximal temporary clipping enables clip reconstruction of vessel segments and preservation of emanating branches.
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