• An open craniotomy is performed to clip an intact, leaking, or ruptured cerebral aneurysm that is untreatable by endovascular embolization. The first clipping was described in 1937; since then, there has been continued evolution of shape and size of clips.
• A frontotemporal or pterional craniotomy is performed and the frontal and temporal lobes are gently retracted. The circle of Willis is exposed and the aneurysm is located. In most cases, the aneurysm has been imaged preoperatively by cerebral angiography to determine the location, shape, and size.
• The blood supply to the aneurysm is determined/confirmed under the microscope. Doppler ultrasound may also be used to determine blood flow around the aneurysm.
• Under microscopic visualization, permanent clips are placed around the neck of the aneurysm to prevent blood from entering the dome; they are MRI and biocompatible. If clipping is deemed to be inadequate, temporary clips are placed across the cerebral vessel while additional clipping and hemostasis is achieved. Temporary clips are large and easy to place and remove; they are placed proximal to the aneurysm to deprive it of blood flow and provide a bloodless field. Prolonged temporary clipping increases the risk of ischemia; thus, clipping time should be closely monitored.
• To confirm the absence of a leak postclipping, one of the following surgeon- and institution-dependent techniques are performed:
  • Angiography. A vascular sheath is placed either preoperatively or intraoperatively (institution-dependent).
  • IV indocyanine green dye (IcG). Can be observed under fluoroscopy while precluding the need for IV contrast dye and placement of a vascular sheath. Strong data, however, is not available at this time to obviate angiography.
  • IcG and angiography. Decreases the length of angiography and exposure to IV contrast dye. Requires placement of a vascular sheath.
• Advantages to craniotomy with aneurysm clipping versus endovascular embolization include definitive aneurysm ablation, lower incidence of rebleeding, decreased cost, and technical superiority in cases where the aneurysm cannot be coiled endovascularly.
• Disadvantages include increased risk of bleeding, stroke, seizure, myocardial infarction, aneurysm rupture, vasospasm, and possibly recovery.

• Supine (prone in rare cases of occipital aneurysms)
• Head pinned in a Sugita (or Mayfield) frame
• Shoulder roll placed and the ipsilateral arm can be folded over the body if there is any tension on the brachial plexus; alternatively, the arm can be tucked.
• If possible, the left arm is left abducted <90° for access to IV, arterial line, and pulse oximetry.
• Bed turned 90–180°

Frontotemporal or pterional incision (occipital rare). Temporalis flap, Burr hole, and then bone flap turned to expose dura.

• Varies depending on aneurysm size, location, and shape. Technical difficulty can arise from the aneurysm's neck shape or blood supply.
• Length can also be prolonged by intraoperative angiography.

• Unruptured aneurysms: ~500–1,000 mL.
• Rupture: In excess of 2,000 mL. Sufficient blood products should be typed and crossed, in the room, and checked in the event that immediate transfusion is needed.

• Unruptured aneurysm: 8–10 days
• Ruptured aneurysm: >8–10 days to manage complications.

• Sugita or Mayfield surgical frame
• Surgical microscope
• A variety of MRI and biocompatible temporary and permanent aneurysm clips
• Angiography and accompanying radiological equipment and personnel versus fluoroscopy for IcG.
• Neuromonitoring equipment and personnel

Incidence

• Cerebral aneurysms are present in 2–5% of the population.
• The incidence of rupture is 1 in 10,000 patients with aneurysms.

Prevalence

• Risk of rupture increases 1–2% per year, peaking between 40 and 60 years of age.
• Increased in females, smokers, polycystic kidney disease, and hypertensive patients.

• Rupture: 30–35% through one's lifetime
• All-cause morbidity at 1-year post-repair: 15.7%
• Stroke from surgery: 1–10%.

1-year post repair: 1.6%

History

• Commonly an incidental finding on brain imaging for other complaints or trauma.
• 1 in 10,000 patients with aneurysms present with subarachnoid hemorrhage (SAH).
• Standard history with focus on neurologic and cardiovascular history.

Signs/Physical Exam

Full neurological exam

Labs/Studies

• CBC, type and cross, chemistry, and coagulation panel
• Head CT, MRI
• Cerebral angiogram

Should be used sparingly; small amounts of midazolam (short duration) or opioid may be administered for preinduction line placement. Avoid other sedatives such as scopolamine, droperidol, or diazepam that may cloud the postprocedure neurological exam.

• Blood consent
• Possibility of postoperative intubation

Gram positive coverage for skin flora with a third-generation cephalosporin

• General anesthesia with endotracheal tube (ETT)
• Very rarely, an "awake craniotomy" (light MAC with scalp block) for aneurysms in eloquent parts of the brain

• Standard ASA monitors
• Foley catheter with urometer
• Arterial line (preinduciton for beat-to-beat monitoring (Cushing response, tight hemodynamic adjustments), and frequent labs (hemoglobin, electrolytes, osmolality)
• Central venous access in patients with SAH, otherwise large-bore (14–18 G) peripheral access is adequate for rapid resuscitation and transfusion.
• Intraoperative neuromonitoring: Usually EEG and somatosensory-evoked potential (SSEP)
• Bispectral monitoring may not be possible because of pin placement or incision.

• Deep induction with hypnotic, opioid, and paralytic medication to avoid coughing, bucking, sharp increases in BP, and hypoxemia with laryngoscopy and intubation.
• Avoid ketamine and succinylcholine as they can increase the ICP. If a RSI is warranted (e.g., SAH, risk of aspiration), the benefit of quickly securing the airway and controlling respiratory parameters outweighs the small and transient increase from succinylcholine.
• Antihypertensives and vasopressors with quick onset and short duration should be available to provide tight hemodynamic control (hypotension can cause ischemia and hypertension can cause rupture).

• Low-dose inhalational agents, opioids (bolus or infusion), and muscle relaxation can be used versus total IV anesthesia with propofol (may have better effects on ICP, brain relaxation, and IONM). Nitrous oxide is generally avoided.
• CO₂. The ETCO₂ is typically maintained between 25 and 30 mm Hg. If concerned about dead space (chronic obstructive pulmonary disease, COPD, pneumonectomy) follow PaCO₂. Hypercarbia can lead to increased cerebral blood flow (CBF) and increased ICP. Rapid drops in CO₂ can increase the transmural pressure of the aneurysm and cause rupture. Severe hypocarbia (<25 mm Hg) can cause ischemia.
• Anticonvulsants should be loaded during the case.
• Corticosteroids (dexamethasone) are given to treat cerebral edema and help prevent PONV.
• ICP. Diuresis with mannitol and the possible addition of a loop diuretic to decrease brain water and volume. Maintain euvolemia by replacing urine output.
• Fluids. Normal saline is preferred due to its high osmolality; however, it can cause a metabolic hyperchloremic acidosis.
• IONM. Communicate anesthetic technique and changes to neuromonitoring to avoid masking or misconstruing changes from the surgical field.
• Tight hemodynamic control. Be prepared to increase BP (with fluids and pressors versus inotropes) during temporary clipping or occlusion of the internal carotid artery to improve collateral flow. Be prepared to return BP to normal after clipping. Avoid hypotension to decrease risk of ischemia.
• Burst suppression with thiopental or propofol may be used during temporary aneurysm clipping.
• Temperature. Mild intraoperative hypothermia (to 33°C) is controversial. Data has not proven any benefit in healthy patients with unruptured aneurysms.

• for uncomplicated cases, extubation followed by a neurological exam is important to identify possible surgical complications. In patients who require postoperative intubation, a neurological exam should be attempted before reanesthetizing and transporting to the intensive care unit (ICU). The inability to perform or an abnormality in the neurological exam requires immediate neuroimaging before transport to the ICU.
• Avoid bucking, coughing, or hypertension
• Patients should remain flat (or reverse Trendelenburg) if an angiography sheath was placed.