Craniotomy

Etiology

Age ranges from 0-85, but typically 20-60

Presenting symptoms: Elevated ICP, seizures, headaches, nausea/vomiting, visual disturbances

The patient may be on steroids to decrease ICP

Hx of chemotherapy or radiation may affect pulmonary or renal function

You may see edema in surrounding tissue leading to increased ICP - if herniation of the brainstem, you'll see Cushing Triad (HTN, bradycardia, irregular respiration)

Coagulation studies should be normal

Neuroanatomy

White matter: myelinated axons (all preganglionic fibers go through white matter to the paravertebral ganglia)

Grey matter: neuron cell bodies in CNS

Neuroglial Cells

Astrocytes

• Most prevalent, support, metabolic, and nutritive functions

Oligodendrocytes

• Insulation from myelin sheath in the brain and spinal cord

Microglial cells

• The smallest neuroglial cell, scattered throughout CNS, is transported to injury sites to do phagocytosis

Ependymal 

• Found in the roof of the 3rd and 4th ventricle and central spinal canal. They form a choroid plexus, which secretes cerebrospinal fluid (CSF) around 30ml/hr

Anatomy CNS

Cerebral cortex

• 3 mm outer layer. The convoluted surface where the elevations are called gyri, the shallow groves separating the gyri are sulci, and the deeper groves fissures. The median longitudinal fissure divides the cerebral hemispheres into right and left

The frontal lobe

Essential for motor control, and the parietal lobe, essential for senses of pain and touch, are separated by the central sulcus Rolando

• Precentral gyrus

Motor control

• Postcentral gyrus

Touch, pain, limb position, sensory perception of grasped objects

Temporal lobe

• The auditory cortex is separated from the frontal and parietal lobes by the Sylvian fissure

Occipital lobe

• Visual cortex

Corpus callosum lies deep in the longitudinal fissure - and connects the hemispheres

Basal ganglia

• Control of movement

Amygdala

• Regulates emotional behavior, pain, and appetite - response to stressors

Hippocampal

• Formation of memory and learning

Diencephalon

• Located midline between the central hemispheres, contains the thalamus (sensory input relay station to cortex) and hypothalamus
  • Releases hypothalamic-releasing hormones to the pituitary gland, controls body temperature, hunger, thirst, sleep, and circadian cycles

Brainstem

• It contains the reticular activating system

Midbrain

• Relay for auditory and visual information, eye movement (VI), contains substantia nigra
  • Control of body movement, ie, Parkinson's

Pons

• Ascending and descending fiber tracts and nuclei of trigeminal V and facial VII nerves

Medulla

• From pons to foramen magnum, which becomes continuous with the spinal cord. The medulla contains ascending and descending fiber tracts, respiratory and cardiovascular centers, and CN VII, IX, X, XI, and XII

Cerebellum

• Below the occipital lobe. Regulates equilibrium and muscle tone and coordinates voluntary muscle activity

Cerebral Meninges

Dura mater

• It has an outer periosteal layer adherent to the inner cranium, and an inner meningeal layer forms a fold, the falx cerebri, which separates the cerebral hemispheres and the tentorium cerebelli, which separates the occipital lobe and the cerebellum
• Innervated by the first three cervical roots and the trigeminal nerve - during awake craniotomy, pt may complain of pain "behind the eye" when traction is applied to the dura

Arachnoid mater

• Thin, avascular membrane

Pia mater

• Thin avascular membrane adherent to the brain and spinal cord

Cerebrospinal Fluid

150 mL, replaced every 3-4 hrs, drains into the venous blood via the superior sagittal sinus and is absorbed by arachnoid granulations.

Normal ICP 5-15 mmHg

Preoperative Diagnosis

Glioma, glioblastoma multiforme, astrocytoma, oligodendroglioma, ependymoma, PNET (primitive neuroectodermal tumor), meningioma, craniopharyngioma, choroid plexus papilloma, hemangioblastomas, medulloblastoma, acoustic neuroma, brain metastasis, hemangiopericytoma

Brain tumors are either Supratentorial (above the cerebellum), infratentorial, intraaxial (within the brain parenchyma), or extraaxial (outside the brain parenchyma)

Surgical Approach

It depends on the location of the lesion

• The need for brain relaxation
• Whether exposure will require brain resection
• Patient positioning depends on location and surgical approach to the tumor
• Supine, lateral, prone, or sitting
• The pts head is often placed in Mayfield pin fixation - VERY PAINFUL. GIVE PAIN MEDICATION
• Mayfield fixation helps with intraoperative image-guided stereotactic navigation (stealth), which is usually coordinated with films from CT/MRI and helps locate optimal access and instruments during surgery

Surgical Procedure

Linear incision: used to resect small tumors, midline approach to posterior fossa

Curvilinear/horseshoe incisions: larger tumors

The skull is exposed, burr holes are made, and the bone flap is cut with the craniotome. A free-bone flap (stored for the duration of the case or replaced later depending on swelling) differs from an osteoplastic flap, where the bone is left connected to muscle and/or pericranium to keep it partially vascularized.

If bone is not replaced after removal, it is called a craniectomy.

When the bone flap is replaced later, it's called a cranioplasty.

Once the bone is removed, a few small holes are drilled near the edge of the craniotomy. This helps suspend the dura using sutures and prevents blood from collecting in the epidural space during the surgery. The dural opening method depends on the bone opening size and its proximity to venous sinuses. The surgeon then continues with tumor removal. Depending on the location (superficial vs. deep), the surgeon may ask for anesthetic intervention for brain relaxation (osmotic diuresis, hyperventilation) and specific blood pressure control.

Once the tumor is removed and the dura is closed, hemostasis is obtained. The surgeon may ask for a specific blood pressure reading to ensure hemostasis. The bone flap is then replaced, and the skin is stapled.

Patients are usually extubated post-procedure for initial neurological evaluation.

Electrophysiologic Monitoring

Type and usage depend on the location of the tumor

Note that a 50% decrease in amplitude or a 10% increase in latency are considered significant

Always communicate with the monitoring technician to ensure adequate impulses

Continuous drips as opposed to boluses

Preoperative Considerations

Surgical Time

3-5 hrs

Antibiotics

Cefazolin 2 g

EBL

50-500 mL

Pain Score

2-7

Mortality

0-5% - higher for tumors in critical locations

Morbidity

Infections 1%

Neurological: neurologic disability, nerve injury 0-10%

CSF leak 1-3%

Venous sinus injury, air embolus

Endocrine disorder

Massive blood loss

Anesthetic Considerations

Premedication - none if elevated ICP as premeds increases ICP

Induction

Deep level of anesthesia if elevated ICP

Maintenance

Isoflurane or sevoflurane< 1 MAC (vasodilation = elevated ICP)

Propofol and remifentanil drips

Consider TIVA anesthesia

Emergence

The surgeon may request transient elevated MAP 90-100 to test hemostasis

You may need labetalol, esmolol, sodium nitroprusside, or nicardipine

HOB elevated 20-30 degrees

Antiemetic 30min prior to extubation

If giving mannitol or furosemide, monitor K levels

Mild hypothermia - neuroprotective

CSF drainage - usually via a lumbar drain. Consider elevated head to facilitate runoff

Postoperative Complications

Seizures

Neurologic deficits

Tension pneumocephalus

Hemorrhage requiring reexploration

Edema and elevated ICP