BRIEF FUNCTIONAL ANATOMY OF THE BRAIN

✔️Precentral gyrus contains the primary motor cortex

✔️Premotor cortex lies immediately anterior to Primary motor cortex ( Brodmann’s area 6 on the lateral surface of the frontal lobe.)

✔️Premotor cortex is active in response to EXTERNAL visual or somatic sensory cues (e.g. reaching for an object in full view, or identifying an object by touch alone). Also has role in bilateral postural fixation (e.g. stabilization of the hips during walking).

✔️The supplementary motor area occupies a neighbouring part of Brodmann’s area 6 on the medial surface of the frontal lobe.

✔️The supplementary motor area seems to respond to INTERNAL cues, especially intentions to make voluntary movements (even if the movement is not carried out).

✔️Lesions of the supplementary motor cortex are associated with contralateral inability to initiate movements (akinesia).

✔️The inferior frontal gyrus of the dominant hemisphere (usually the left) contains the (Broca’s) motor speech area (Brodmann’s areas 44 and 45)

✔️The somatic sensory cortex, occupies the entire postcentral gyrus (Brodmann’s areas 3, 1 and 2, rostral to caudal).

✔️ Caudal to the somatosensory cortex is the sensory association cortex, which is divided into a superior and an inferior parietal lobule by an intraparietal sulcus.

✔️ The superior lobule is thought to be responsible for conscious awareness of the contralateral half of the body. Lesions of this part of the cortex may result in neglect of the contralateral side of the body.

✔️ The inferior lobule in the dominant (usually left) hemisphere is associated with language functions.

✔️ The cortex adjacent to the parieto-occipital sulcus and the calcarine sulcus, which lies on the medial surface of occipital lobe, constitutes the primary visual cortex (Brodmann’s area 17).

✔️ The superior surface of the temporal lobe contains the primary auditory cortex (Brodmann’s areas 41 and 42), responsible for the conscious perception of sound. Unilateral lesions of the primary auditory cortex will therefore cause partial deafness in both ears.

✔️ The auditory association cortex, known as Wernicke’s area corresponds to Brodmann’s area 22 in the dominant hemisphere. It allows for understanding of the spoken word, and connects with other language areas of the brain.

✔️ The temporal lobe curls inward to form the hippocampus which lies in the floor of the inferior horn of the lateral ventricle, and forms part of the limbic system. Its functions relate to short-term memory and the emotional aspects of behaviour.

✔️ Lying close to the anterior end of the hippocampus is the amygdala. Its a mass of subcortical grey matter that also forms part of the limbic system. It is associated with the conscious appreciation of smells.

✔️ The insula is one of the cortical centres for pain, and is also involved in involuntary activities such as the control of viscera by the autonomic nervous system.

✔️ The basal ganglia includes

• striatum (caudate nucleus, putamen of the lentiform nucleus and the nucleus accumbens) 

• pallidum (globus pallidus of the lentiform nucleus) 

• subthalamic nucleus 

• compact part of the substantia nigra 

✔️ Four basic circuits are known to occur from the cerebral cortex, through the basal ganglia and back to the cortex, by a direct or indirect route: 

-a motor loop is concerned with learned movements;

-a cognitive loop with motor intentions; 

-a limbic loop with emotional aspects of movement and 

-an oculomotor loop with voluntary saccades.

✔️ Limbic system is composed of the the parahippocampal and cingulate gyri, the septal area, the hippocampal formation and the amygdala. Declarative memory (i.e. of new facts and events) may occur as modifications of synapses within the hippocampus.

✔️ Diencephalon comprises, from superior to inferior, the epithalamus, thalamus, subthalamus and hypothalamus.

✔️ The thalamus is the largest component of the diencephalon and is composed of numerous nuclei.

✔️ The epithalamus consists principally of the pineal gland that secretes melatonin and is involved with circadian rhythm and regulation of the onset of puberty and the habenular nuclei.

✔️ The subthalamus contains the subthalamic nucleus which connects to the globus pallidus and substantia nigra and is involved with the control of movement.

✔️ The hypothalamus has important connections with the limbic system, a controlling influence on autonomic nervous system activity and a role in neuroendocrine function.

✔️ The cerebellum coordinates movement by maintenance of equilibrium, posture and muscle tone at an unconscious level. Also concerned with muscular coordination, including trajectory, speed and force of movements.

✔️ The tectum (roof) of the midbrain is formed by four colliculi –the paired superior colliculi are associated with the visual system, and the inferior colliculi with the auditory system.

Reference: The brain: functional divisions, Leo Donnelly, Neurosurgery, Neuroradiology & Neurocritical Care in Anaesthesia

FACTORS CAUSING FLUID AND ELECTROLYTE DISTURBANCES IN THE NEUROSURGICAL PATIENT

✅POOR ORAL INTAKE LEADING TO DEHYDRATION DUE TO

🔖 Decreased conscious level

🔖 Vomiting

🔖 Bulbar dysfunction 

🔖 Pending surgery 

✅FLUID OVERLOAD DUE TO

🔖overzealous intravenous rehydration 

✅DRUGS

🔖osmotic or loop diuretic therapy as part of the management of raised ICP

✅DISORDERS OF SODIUM-WATER BALANCE ASSOCIATED WITH THE NEUROLOGICAL PATHOLOGY/ SURGERY

🔖Syndrome of inappropriate antidiuretic hormone secretion (SIADH)

🔖Cerebral salt wasting (CSWS) 

🔖Diabetes insipidus

Systemic complications of aneurysmal subarachnoid hemorrhage

🔺Hypovolemia

🔺Hyponatremia

🔺Hypokalemia

🔺Hypocalcemia

🔺Electrocardiographic abnormalities

🔺Pulmonary edema

🔺Pneumonia

🔺Pulmonary embolus

🔺Hepatic dysfunction

🔺Renal dysfunction

🔺Thrombocytopenia

🔺Gastrointestinal bleeding

SURGICAL APPROACHES FOR VARIOUS ANEURYSMS

🌀FRONTO TEMPORAL (PTERIONAL ) CRANIOTOMY 

🔺Allows access to most aneurysms on lateral and anterior Circle of Willis vessels.

🔺Internal Carotid : Paraclinoid / Superior hypophyseal artery

🔺Internal Carotid : Ophthalmic artery

🔺Posterior Commununicating Artery

🔺Anterior Choroidal artery

🔺Internal Carotid Bifurcation 

🔺Middle Cerebral Artery

🔺Anterior Commununicating Artery

🌀PTERIONAL / SUBTEMPORAL APPROACH 

🔺Upper Basilar Artery

🔺Superior Cerebellar Artery

🌀SUBOCCIPITAL APPROACH 

🔺Vertebral Artery

🔺Posterior Inferior Cerebellar Artery

🌀COMBINED SUBTEMPORAL AND SUBOCCIPITAL APPROACH 

🔺Basilar trunk

🔺Vertebrobasilar Junction

INTRACRANIAL ANEURYSMS : GENETICS AND ASSOCIATED DISEASES

Of patients who have SAH from ruptured aneurysm, 5% to 10% will have one or more first-order relatives who have also had a ruptured aneurysm. 

The inheritance is probably dominant with variable penetrance. 

Conditions associated with intracranial aneurysms include 〰〰〰〰〰〰〰〰〰〰〰〰〰〰〰〰〰

🏷polycystic kidney disease (5% of aneurysms series, 33% of polycystic kidney series)

🏷coarctation of the aorta (1% of aneurysm patients, 5% of coarctation patients, all of whom are hypertensive)

🏷sickle cell disease

🏷drug abuse (cocaine: generalized vasoconstriction and hypertension; intravenous use: mycotic aneurysms)

🏷hypertension (30% to 40% of patients with SAH). 

Rarer associations 

〰〰〰〰〰〰〰

🏷fibromuscular dysplasia

🏷Marfan's syndrome

🏷tuberous sclerosis

🏷Ehlers-Danlos syndrome

🏷hereditary hemorrhagic telangiectasia

🏷moyamoya disease

🏷pseudoxanthoma elasticum. 

🏷Choriocarcinoma 

🏷cardiac myxomas 

Ref: Handbook of Neuroanesthesia, 4th Edition, p:144

Predisposing factors for rebleeding after Aneurysmal SAH

🔹Large volume of blood in the subarachnoid space from the initial SAH

🔹Poor neurologic status owing to the devastation caused by the initial SAH

🔹Short interval from the initial hemorrhage

🔹Female gender: women rebleed twice as frequently as men

🔹Older age and poor general medical condition

🔹Systemic hypertension: the risk of rebleeding is directly related to the patient's systolic blood pressure

🔹Multiple previous episodes of rebleeding that increase the likelihood of subsequent rupture and death

🔹Presence of either an intracerebral or intraventricular hematoma

🔹Abnormal clotting parameters

🔹Posterior circulation aneurysms

Ref: Philippa Newfield, Audrée A. Bendo, Handbook of Neuroanesthesia, 4th Edition, 2007 Lippincott Williams & Wilkins

ANTERIOR AND POSTERIOR APPROACHES TO CERVICAL SPINE / SAFE Anesthesiologist Series [Surgical Aspects For Empowering Anesthesiologist]

ANTERIOR APPROACH TO CERVICAL SPINE

➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖

✔️ADVANTAGES

Easy access to disc

Little pain

Evacuate disc

Fusion by plate or graft

✖️DISADVANTAGES 

Multiple levels difficult 

May require fusion if unstable

Loss of mobility 

Risk of injury to adjacent structures

POSTERIOR APPROACH TO CERVICAL SPINE

➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖➖

✔️ADVANTAGES

Access to multiple levels

Direct visualisation of root

Fusion is usually not required

✖️DISADVANTAGES 

Risk of instability 

Poor access to disc space

Poor access to osteophytes

Higher risk of cord injury

Painful procedure

Ref: Bailey & Love’s Short Practice of Surgery, 24/e

ANAESTHETIC IMPLICATIONS IN EPILEPSY SURGERIES

✔️If Awake Craniotomy/ wake up testing is planned, the procedure details should be explained to the patient, including what he/she is expected to hear and feel, inside the O.R.

✔️Get a brief description of the seizures and any prodromal symptoms 

✔️Continue anti epileptics through the morning of surgery

✔️Antiepileptics can reduce duration of action of NMBAs

✔️Usually a preoperative WADA test or fMRI would have been done, to check, whether the side of proposed surgery has any cerebral dominance or speech function 

✔️Abnormal LFTs can be expected with long term Valproate or Carbamazepine therapy

✔️WHAT THE COMMON AEDs DO?

✔️Phenytoin and Phenobarbitone: Reduce Hematocrit

Carbamazepine, Valproate,Ethosuximide and Primidone : Reduce platelet count

Carbamazepine and Primidone: Reduce WBC count

✔️If a difficult intubation is anticipated ( for e.g. After fixation of stereotactic frame ), an awake fibreoptic intubation can be considered 

✔️Moderate Sedation, if required can be achieved with Propofol 25-75 ug/kg/min plus Remifentanil 0.02-0.05 ug/kg/min OR Dexmedetomidine 1ug/kg/min over 10 minutes followed by 0.2-0.7 ug/kg/min

✔️Anticipated Surgical duration: 3 hours

✔️EBL: 250-500 ml ; blood transfusions are seldom needed

✔️Pain score 2-4

✔️If an Asleep-Awake-Asleep technique is used:

GA  continued for positioning, craniotomy and till the exposure of the surgical area. Then patient is allowed to awaken, to monitor neurological function during brain stimulation ( LMA removed OR  if ETT, it is removed over a tube exchanger). When seizure area, is fully delineated, GA is reinstituted.

AETIOLOGIES AND ASSOCIATED CONDITIONS IN PATIENTS COMING FOR EPILEPSY SURGERY

AETIOLOGIES 

〰〰〰〰〰

🏷Idiopathic (Mesial Temporal Sclerosis)

🏷Infectious (Brain Abcess, Encephalitis)

🏷Traumatic (glial scar)

🏷Vascular (AVM, Infarct)

🏷Neoplastic (glioma, hamartoma, ganglioglioma)

🏷Congenital (Cortical dysplasia)

ASSOCIATED CONDITIONS 

〰〰〰〰〰〰〰〰〰〰

🏷Tuberous Sclerosis

🏷Sturge Weber Syndrome 

🏷Infantile Hemiplegia

🏷Encephalitis

EPILEPSY SURGERY: OTHER APPROACHES

💈1) Frontal/temporal or occipital craniotomy for resection of a structural epileptogenic focus e.g. Tumour or AVM

🔺This may use stereotaxic localisation (by using a stereotaxic headframe, which may affect the method of intubation)

💈2) Diagnostic placement of surface or depth electrodes

 🔺Mostly only burr holes outlining the future craniotomy flap are used

🔺After placement, the electrodes are externalised and postoperatively patient’s naturally occurring seizures are recorded in conjunction with video monitoring, to register the clinical presentation, with the onset of seizure activity. This recording period may last for several days.

🔺This will be followed by resection of the epileptic focus, on another date.

💈3) Selective amygdalo-hippocampectomy

🔺Here, a cortical incision is made in the anterior temporal lobe and amygdala & hippocampus are resected

EPILEPSY SURGERY- VARIANT APPROACHES🙇🙇🏻🙇🏼🙇🏾: CORPUS CALLOSOTOMY

✔️Suited for patients with atonic or partial seizures with secondary generalisation 

✔️Either the anterior 2/3rd or the entire corpus callosum is divided in the midline

✔️Uses a bifrontal paramedian scalp incision and elevation of the free bone flap, adjacent to the midline in the region of the coronal suture

✔️Injury to the sagittal sinus can result in massive VAE or haemorrhage 

✔️Preserve the numerous bridging veins across the interhemispheric fissure; otherwise, can result in venous congestion and possible infarction 

✔️Right cerebral hemisphere is gently retracted from the falx: this will expose the paired anterior cerebral arteries and corpus callosum

#epilepsy , #seizures ,#neurosurgery , #EpilepsySurgery , #NeuroAnaesthesia ,#NeuroAnesthesia , #speech ,#wadatest

EPILEPSY SURGERY: SPECIFIC PROCEDURES & HIGHLIGHTS : TEMPORAL LOBECTOMY

✔️ Head turned 90* and held with pins

✔️ Most commonly a "question mark" temporal incision

✔️ a flap based on temporalis muscle elevated

✔️ a subtemporal craniectomy allows visualisation of entire anterior temporal lobe

✔️ anterior 6-6.5 cms of temporal lobe exposed

✔️ surface or depth electrocorticography employed

✔️ map the lesion

✔️ amygdala, hippocampus/ anterior temporal lobe removed 

✔️ Temporal lobectomy involves resection of both lateral and medial (uncus, hippocampal formation etc) temporal structures, mostly under an operating microscope

✔️ Complications: Injury to brainstem, 3rd and 4th cranial nerves , Middle or Posterior Cerebral arteries

✔️ closure of dura, bone flap and scalp concludes the surgery

#epilepsy , #seizures ,#neurosurgery , #EpilepsySurgery , #NeuroAnaesthesia ,#NeuroAnesthesia , #speech ,#wadatest

☁️EPILEPSY SURGERY: BASIC FACTS

☄Most beneficial in partial seizures secondary to a structural lesion

☄For determining the cerebral dominance and hence the location of speech , a WADA test (intracarotid injection of anesthetic to localize language function ; hence invasive) or recently functional MRI mapping (non invasive) of speech centres are done preoperatively 

☄Simultaneous recordings of video EEG and MRI or PET scans can show the epileptogenic focus

☄Temporal lobe surgery may involve:

✔️removal of only the structural lesion & associated epileptogenic cortex

✔️cortical resection alone

✔️excision of amygdala and hippocampus 

✔️removal of the entire anterior temporal lobe (extent of posterior resection dependent on dominance)

✔️depending on the local protocol, intraoperative Electro Corticogram (ECoG) may be used; anesthesia has to be modified accordingly

✔️if speech centre has to be located intraoperatively, an awake craniotomy is required

✔️ So depending on the surgical plan, choice of anesthesia varies

TRAMADOL AND ONDANSETRON: THEY ARE NOT A GOOD PAIR ! ; WHY FORCING THEM TO LIVE TOGETHER ?

Tramadol- highlights 

➖➖➖➖➖➖➖➖

✔️both opioid and non-opioid modes of action. . 

(1) inhibition of noradrenaline re-uptake 

(2)increased release and decreased re-uptake of serotonin in the spinal cord, and 

(3)a weak effect on mu opioid receptors

✔️The weak, opioid effect is mediated by an active metabolite, (+)-M1 (O-desmethyltramadol), formed via the genetically polymorphic P450 CYP2D6 iso-enzyme system. The biological activity of this system is variable, and individuals may be classified as extensive or poor metabolisers of tramadol. 

✔️Tramadol’s affinity for opioid receptors is about 6000 times weaker than morphine, but the (+)-M1 metabolite has an affinity about 200 times greater than tramadol. Poulsen et al. report much higher concentrations of the (+)-M1 metabolite and greater analgesic efficacy of tramadol in extensive metabolisers compared to poor metabolisers. Also noted was a reduction of nausea, vomiting and tiredness amongst poor metabolisers

Ondansetron-highlights

➖➖➖➖➖➖➖➖➖

✔️Ondansetron competitively antagonises serotonin, subtype 3 (5-HT3) receptors in the CTZ and enteric neurones. 

✔️ Peripheral 5-HT3 receptors are also involved in nociceptive pathways and ondansetron may alter 5-HT3 nociceptive responses at the level of dorsal horn neurones

✔️ Ondansetron can block sodium channels in a similar fashion to local anaesthetic agents, and exhibit agonist activity at mu opioid receptors, thus resulting in a peripheral anti-nociceptive effect.

Tramadol + Ondansetron 

➖➖➖➖➖➖➖➖➖

✔️PONV due to Tramadol is often managed with a competitive serotonin antagonist, ondansetron

✔️ There is evidence that the concurrent use of these two drugs results in a mutual reduction of effect—tramadol is a less potent analgesic and ondansetron is a less effective as an antiemetic. 

✔️ But the effect of ondansetron on tramadol consumption diminished with time. 

✔️ De Witte et al. found a significant (50%) increase in cumulative tramadol consumption during the first post-operative hour when patients were given ondansetron along with Tramadol.

✔️ Ondansetron is, in part, metabolised by the CYP2D6 iso-enzyme system—an iso-enzyme system responsible for formation of an active tramadol metabolite that has analgesic effect . Competition for this metabolic pathway may result in a reduction in formation of the (+)-M1 metabolite of tramadol and a consequent reduction in analgesic efficacy.

DO YOU KNOW❓😳 additional points➕

✔️ There is animal and human evidence that both tramadol and ondansetron have local anaesthetic type properties.

✔️ Ondansetron was approximately fifteen times more potent than lignocaine and may well be a prototype molecule for the development of a new group of local anaesthetic agents. 

✔️ These findings are further supported in a human clinical study by Memis et al.which showed that tramadol and ondansetron both significantly reduced the pain associated with the injection of the neuromuscular blocking drug, rocuronium.

(Ref: J.H. Ye, W.C. Mui, J. Ren, T.E. Hunt, W.H. Wu, V.K. Zbuzek Ondansetron exhibits the properties of a local anesthetic. Anesth. Analg., 85 (1997), pp. 1116–1121)

✔️Tropisetron and granisetron are able to reverse an acetaminophen-mediated analgesia completely.

 

〰〰〰〰〰〰〰〰〰〰〰〰〰〰〰〰〰〰〰〰〰

References:

Anaesthesia. 2015 Feb;70(2):209-18. doi: 10.1111/anae.12948. Epub 2014 Dec 10.

The effect of ondansetron on the efficacy of postoperative tramadol: a systematic review and meta-analysis of a drug interaction.

Stevens AJ1, Woodman RJ, Owen H.

Ondansetron Inhibits the Analgesic Effects of Tramadol: A Possible 5-HT3 Spinal Receptor Involvement in Acute Pain in Humans

Arcioni, Roberto MD*,; della Rocca, Marco MD*,; Romanò, Sarah MD*,; Romano, Rocco MD†,; Pietropaoli, Paolo MD*, and; Gasparetto, Alessandro MD*

ScienceDirect Review

Aspects of tramadol and ondansetron interactions Bruce Hammonds, David A. Sidebotham, Brian J. Anderson,

📝BRAIN TUMOURS-SYMPTOMATOLOGY

📌Contralateral signs :  are associated with lesions in the posterior frontal area (motor) or anterior parietal lobe (sensory)

📌Lesions in the dominant hemisphere: Aphasia

📌Lesions in the non dominant hemisphere: Apraxia

📌Temporal lobe lesions : Focal seizures with auras and visual field defects

📌Frontal lobe lesions : Altered cognitive functioning and subtle personality changes

📌Subfrontal lesions : Anosmia

📌Sellar and Parasellar lesions: Visual field and Acuity problems , hypopituitarism, oversecretion syndromes (Cushing Syndrome, Acromegaly)

📌Tumours in relation to Ventricular system : Hydrocephalus , Raised ICP

📌Tumours of the brainstem and cerebellopontine angle : Cranial nerve palsies , long tract signs , secondary hydrocephalus

📌Lesions of Cerebellar vermis : Truncal ataxia

📌Lesions in Cerebellar hemisphere: Appendicular signs such as incoordination and nystagmus 

Reference:

Page :617-618, Bailey and Love’s , SHORT PRACTICE OF SURGERY , 24 th edition