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NEUROANATOMY By Yusuf Alkhateeb LayersoftheSCLAP To help you remember the layers of the scalp, use the mnemonic ‘SCALP’. S: Skin C: Connective Tissue (Dense) A: Aponeurosis L: Loose Connective Tissue P: Pericranium CranialBones To help you remember the 8 cranial bones, remember the mnemonic ‘Eight Osseous Parts Form The Skull’. Eight: Ethmoid Osseous: Occipital Parts: Parietal (2) Form: Frontal The: Temporal (2) Skull: Sphenoid Cranium 3 fossae: Each contain openings for cranial nerves. CN I and II exit the anterior cranial fossa. CN III to VI exit the middle cranial fossa. CN VIII to XII exit the posterior cranial fossa. NEUROANATOMY EXTERNALBRAIN The cerebral cortex consists of 4 lobes: Frontal, Temporal, Parietal and Occipital. Each lobe is generally responsible for different function. The brainstem is primarily responsible for involuntary responses. It is made up of the midbrain, pons and medulla oblongata. The cerebellum is part of the hindbrain and is directly connected to the midbrain via the cerebellar peduncles. Gyri: Ridges of the cortex. Sulci: Grooves that form the gyrus. Gyri and sulci help increase surface area of the brain and hence cognitive abilities. Corticalfunction The cerebral cortex can be organised according to functional anatomy. NEUROANATOMY Meningeallayers The meninges are made up of three layers: Dura mater: It is the outermost layer of the meninges. It has two layers of connective tissue: Periosteal layer: Stuck to the inside of the cranial vault. Meningeal layer: Stuck to the arachnoid mater. Arachnoid mater: It is the middle layer of the meninges. It is avascular and doesn’t receive any innervation. Below the arachnoid mater is the sub-arachnoid space. This contains cerebrospinal fluid. Arachnoid granulations allow cerebrospinal fluid to re-enter the circulation via the Dural venous sinuses. Pia mater: It is located below the sub-arachnoid space and is highly vascularised to supply underlying neural tissue. NEUROANATOMY DuralFOLDS The three dural folds include: Falx cerebri: Partly divides the cerebral hemispheres. Tentorium cerebelli: Separates the cerebrum from the cerebellum. Falx cerebelli: Partly divides the cerebellar hemispheres. Arterialsupply The two main arteries that enter the skull and supply the brain are: Internal carotid artery which enters through the carotid canal. Vertebral artery which enters through the foramen magnum. The three arteries supplying the cerebrum include: Anterior cerebral artery which supplies the medial surface. Middle cerebral artery which supplies the lateral surface. Posterior cerebral artery which supplies the posterior surface. NEUROANATOMY CircleofWILLIS The Circle of Willis is an anastomotic ring of arteries located at the base of the brain. It provides collateral blood flow between the anterior and posterior arterial systems of the brain. Blood supply to the brain is via the internal carotid arteries and the vertebral arteries. The Vertebral arteries give off the basilar artery. The carotids and basilar arteries anastomose to for a circle around the optic chiasm. This is referred to as the circle of Willis. The anterior, middle, and posterior cerebral arteries arise from the Circle of Willis. The cerebral arteries divide to form the pial arteries that run over the surface of the brain. Smaller arteries from the pial arteries penetrate the brain. Venousdrainage Venous blood drains into the dural venous sinuses located between the two layers of the dura mater. This then drains into the internal jugular veins. GLIOMAS Tumours stemming from glial cells. Classification Diagnosis Grade I: low-grade gliomas, slow- First line: CT head imaging + growing and resembling normal IV contrast glial cells, with minimal invasion of MRI: Helps characterize and surrounding brain tissue. assess lesion Grade II: aka diffuse Biopsy: Confirm diagnosis astrocytomas, (either via burr hole or open oligodendrogliomas, or exploration i.e. craniotomy oligoastrocytomas, these tumours are slightly more aggressive, with infiltrative growth into nearby brain tissue. Grade III: Anaplastic gliomas, are more malignant and grow faster than grade II gliomas. Grade IV: Glioblastoma multiforme (GBM), the most aggressive type. Highly malignant, grows rapidly, and has a poor prognosis. Management Clinicalfeatures Low grade: Watch and wait Seizures (most common) Cranial nerve palsies Surgery (total or partial Visual field defects tumour debulking) Radiotherapy Language dysfunction High grade: Features of raised intracranial pressure Total or partial tumour debulking (gold standard MENINGIOMA Meningiomas arise from the arachnoid cap cells of the meninges. They usually have clear boundaries and expand outward from the brain or spinal cord's surface. Although most are benign, they can lead to complications because of their location and pressure on nearby structures. Classification Diagnosis Grade I: First line: CT head imaging + Benign meningiomas IV contrast Most common type. MRI: Helps characterize and Grow slowly and tend to have a assess lesion well-defined border between Biopsy: Confirm diagnosis the tumour and surrounding (either via burr hole or open brain tissue. exploration i.e. craniotomy Grade II: Atypical meningiomas More aggressive features than grade I tumours May exhibit higher rates of recurrence post resection. Grade III: Anaplastic meningiomas (malignant meningiomas) More aggressive. They grow rapidly and are more likely to invade surrounding tissues. Management Clinicalfeatures Endovascular Embolization Seizures (most common) Surgical Removal Radiotherapy Cranial nerve palsies Visual field defects Chemotherapy Language dysfunction Features of raised intracranial pressure SPINAL CORD COMPRESSION Diagnosis Aetiology Neoplastic (MSCC = most common) Gold standard: MRI of the Traumatic (via vertebral fracture) whole spine (done within a Infective week if MSCC is suspected) Disc prolapse Blood tests (Routine + Group Infections (via abscess formation) & Save) Inflammatory conditions: Referral to neurosurgery + Rheumatoid arthritis, Ankylosing oncology Spondylitis Clinicalfeatures Neck or back pain Radicular pain (pain that radiates along the path of a nerve) Weakness or numbness in the arms or legs Loss of coordination or balance Difficulty walking or standing Upper motor neuron signs (e.g. hypertonia, hyperreflexia, Babinski sign Autonomic involvement: bowel incontinence, constipation or urinary retention CAUDA EQUINA SYNDROME The cauda equina is a collection of nerve roots that start from L3 onwards and exit from either side of the spial column at their vertebral level (L3, L4, L5, S1, S2, S3, S4, S5) The cauda equina supplies: Sensation: Lower limbs, perineum, bladder, and rectum Motor: Lower limbs and the anal and urethral sphincters Parasympathetic: Bladder and rectum Classification CAUSES Cauda Equina Syndrome with Disc herniation (most Retention (CESR): common) Presents with back pain and Trauma unilateral/bilateral sciatica Neoplasm Includes lower limb motor Infection weakness and sensory disturbance clinicalFEATURES Typically involves urinary retention Severe low back pain Incomplete Cauda Equina Bilateral leg pain, weakness, Syndrome (CESI): or numbness Similar symptoms to CESR Urinary retention or Altered urinary sensation, such incontinence as loss of desire to void, Faecal incontinence or diminished sensation, poor constipation stream, and the need to strain Saddle anaesthesia (loss of Painful retention may precede sensation in the area painless retention in some cases corresponding to a saddle) Suspected Cauda Equina Syndrome Sexual dysfunction (CESS): Severe back and leg pains Variable neurological symptoms and signs Suggestive of sphincter disturbance, but diagnosis not confirmed. CAUDA EQUINA SYNDROME Diagnosis Management Gold standard: Lumbar-sacral Urgent surgical spine MRI decompression: lumbar Examination decompression (+/- Post-void bladder scan discectomy).