Neurosurgery Introduction and Anatomy

Neurosurgery

This chapter will be including the following items which will be discuss separately and these items are

Introduction
Anatomy of the scalp skull brain spinal cord
Diagnostic methods
Neurologic and Neutologic emergencies
Trauma eg.Head .Spinal .Peripheral nerve trauma
Cerebrovascular disease eg Ishemis Thrombotic Embolic, Haemorrhagic Disease
Tumours of the central nervous system eg Intracranial , Metastatic ,Glial ,Neural Crest .Miscellaneous ,Emryologic and Spinal Tumours

Spine Stability Neural Compression Patterns of disease Spinal fusion surgery Spinal instrumentation Arthrodesis
Peripheral Nerve Tumours Entrapment NeuropathiesAutoimmune and Inflammatory Disorders
Infection Cranial eg Brain abscess Osteomylilitis ,Subdural Empyema ,and Spine ,
Functional Neurosurgery
Deep brain stimulators eg Essential tremors and Parkinson,s disease
Trigeminal Neuralgia
sterotactic Radiosurgery eg Arteriovenous malformations Vestibular Shwanomas Intracranial Metastasis
Congenital and Developmental Anomalies
Hydrocephalus
Brain death

Introduction

Neurologic surgery is a discipline of medicine and the specialty of

surgery that provides the operative and nonoperative management (i.e., prevention, diagnosis, evaluation, treatment, critical care. and rehabilitation) of disorders of the central, peripheral, and autonomic nervous systems, including their supporting structures and vascular supply; the evaluation and treatment of pathologic processes that modify the function or activity of the nervous system, including the hypophysis: and the operative and nonoperative management of pain. As such, neurologic surgery encompasses the treatment of adult and pediatric patients with disorders of the nervous system. These disorders include those of the brain, meninges, skull and skull base, and their blood supply, including surgical and endovascular treatment of disorders of the intracranial and extracranial vascula­ ture supplying the brain and spinal cord; disorders of the pituitary gland: disorders of the spinal cord, meninges, and vertebral column, including those that may require treatment by fusion, instrumenta­tion, or endovascuJar techniques; and disorders of the cranial and spinal nerves throughout their distribution.

An accurate history is the first step toward neurologic diagnosis. A history of trauma or of neurologic symptoms is of obvious interest.
but general constitutional symptoms also are important. Neurologic
disease may have systemic effects. while diseases of other symptoms may affect neurologic function. The patient's general medical ability
to withstand the physiologic stress of anesthesia and surgery should be understood a detailed history from the patient and or family along with a reliable physical examination will clarify these issues

ANATOMY

The scalp

There are five layers to the scalp: skin, dense connective tissue, galea aponeurotica, loose connective tissue and pericranium. The scalp receives a rich vascular supply.This arises from

both the external and internal carotid arteries, with the blood vessels lying within the dense connective tissue layer.The ante­rior scalp is supplied by the supratrochlear and supraorbital arter­ies, with additional supply from the internal carotid via the ophthalmic artery. The lateral and posterior scalp is supplied by the superficial temporal, posterior auricular and occipital arteries, and branches of the external carotid. The sensory nerves run with the arteries and are derived from the trigeminal nerve at the front and sides. The posterior aspect is supplied by the greater and lesser occipital nerves with motor supply to the occipitofrontalis muscle by the facial nerve. Venous drainage of the face and ante­rior scalp is via the facial vein. The lateral and posterior aspects are drained by the external jugular vein and the vertebral venous

. plexus respectively.The veins of the scalp and face communicate directly with the intracranial. venous sinuses via emissary veins hence infections in the nasal region'have the potential to causes cavernous sinus thrombosis. Lymph drainage from the scalp is the preauricular and occipital lymph nodes.

The walls of the vessels in the dense connective layer are bound, preventing ready retraction when divided. Incisions in scalp therefore bleed copiously

Lesions that occur on. the head may be identical to these occurring in the skin elsewhere . Therefore any mobile lesion occurring within the skin should be inspected investigated and treated using the usual diagnostic criteria However,when lesions occur in the midline or appear to be more deeply connected within the layers of the scalp, then more extensive radiological investigations ideally,computerised tomography(CT) or magnetic resonance imaging (MRI) should be performed to exclude any intracranial extension

. The skull

The skull consists of several bones that are fused by means sutures to form the cranium, which encases the brain and from which the face hangs. The normal skull has a remarkable degree of symmetry about the midline. There is rapid growth of the skull during the first few year. of life. a growth which is driven and shaped by.the underlying developing brain and the development of the sphenoid bone. Most growth occurred by 2 years, and thereafter it is the facial bones that continue growing,increasing the size of the head. If the development of the brain is abnormal, then this can be reflected in the overall skull size thus
marocephaly may occur as a result of hydrocephalus if premature closure of any of the cranial sutures occurs, this may result in loss of midline symmetry and associated developmental abnormalities of the face. The most common type of synostosis is that of the sagittal suture, which results in the characteristic keel­
shaped head or scaphocephaly while trigonocephaly is caused by premature fusion of the metopic suture whereas plagiocephaly will result from unilateral coronal or­ lambdoid synostosis. When more than one suture is involved in the synototic process , this may result in elevation of the intracranial pressure. There may be restriction of calvarial growth but also obstruction to venous drainage at the base of skull combined with respiratory problems. These are commonly associated with syndrormc craniosynostoses such as
Crouzon and Apert syndromes. Surgery for craniosynostoses is undertaken in specialized units, and because of the associated otolaryngological, dental and ophthalmological implications the
approach should be multidisciplinary. Surgery is directed towards
increasing the volume of the skull, improving the cosmetic defor­mity, and overcoming airway problems that may contribute to morbidity.
Congenital defects of the skull may occur at any point in the midline from the nasion to the foramen magnum as a result of incomplete fusion. Meningeal prolapse that occur with these defects may contain cerebral tissue and likewise be associated with a degree of structural abnormality of the underlying brain.

Brain and Spinal cord

An understanding of neuroanatomy is the foundation of compre­hensive neurologic examination and diagnosis. Salient features will be considered, from cephalad to caudad. The cerebral hemispheres (or telencephalon) consist of the cerebral cortex. underlying white matter, the basal ganglia, hippocampus, and amygdala. The cerebral cortex is the most recently evolved part of the nervous system. Its
functions are mapped to discrete anatomic areas. The frontal areas
are involved in executive function. decision making. and restraint of emotions. The motor strip, or precentral gyrus. is the most posterior component of the frontal lobes, and is arranged along a homunculus with the head inferior and lateral to the lower extremities superiorly and medially. The motor speech area (Broca's area) lies in the left posterior inferior frontal lobe in almost all right-handed people and in up to 90% of left-handed people. The parietal lobe lies between the central sulcus anteriorly and the occipital lobe posteriorly. The postcentral gyrus is the sensory strip, also arranged along a ho­munculus. The rest of the parietal lobe is involved with awareness of one's body in space and relative to the immediate environment,

body orientation, and spatial relationships. The occipital lobes are most posterior. Tbe visual cortex is arrayed along the apposing medial­ surfaces of the occipital lobes. The left occipital lobe receives
and integrates data from the left half of each retina. A left occipi­tal lesion would therefore result in inability to see objects right of center. The temporal lobes lie below the sylvian fissures. The hip­pocampus, amygdala, and lower optic radiations Meyer's loop are important components of the temporal lobe. They are involved
in memory, emotion, and visual pathways, respectively. The recep­tive speech area (Wernicke's area) lies in the area of the posterior superior temporal lobe and the inferior parietal lobe, usually on the
left. The basal ganglia include the caudate, putamen, and the globus pallidus. Basal ganglia structures are involved with modulation of Lying deep to the cerebral hemispheres is the diencephalon.
which includes the thalamus and hypothalamus. The thalamus is a key processor and relay circuit for most motor and sensory in­ formation going to or coming from the cortex. The hypothalamus, at the base of the brain, is a key regulator of homeostasis, via the autonomic and neuroendocrine systems.
The brain stem consists of the midbrain (mesencephalon). pons (metencephalon), and medulla (myelencephalon). Longitudi­nal fibers run through the brain stem, carrying motor and sensory information between the cerebral hemispheres and the spinal cord. The corticospinal tract is the major motor tract, while the medial lemniscus and the spinothalamic tracts are the major sensory tracts. The nuclei of cranial nerves 111 through X11 are also located within the brain stem. These nerves relay the motor, sensory, and special sense functions of the eye. face. mouth, and throat. The cerebel­lum arises from the dorsal aspect of the brain stem. It integrates somatosensory, vestibular, and motor information for coordination and timing of movement. Midline. or vermian, lesions lead to truncal ataxia
. Lateral, or hemispheric, lesions lead to tremor and dyscoor­dination in the extremities
The ventricular system is a cerebrospinal fluid (CSF) containing contiguous space inside the brain. continuous with the subarachnoid space outside the brain. The paired lateral ventricles consist of temporal­ , occipital, and frontal horns, as well as the main body. CSF.travels from each lateral ventncle through the foramina of Monroe­ to the third ventricle, located between the left and right tha­lmi. CSF then drains through the cerebral aqueduct to the fourth ventricle in the brain stem. The foramen of Magendie (midline) and paired foramina of Luschka (lateral) drain to the subarachnoid space
Choroid plexus creates the CSF, mostly in the lateral ventricles­The average adult has an approximate CSF volume of 150 mL and creates approximately 500 mL per day.
The spinal cord starts at the bottom of the medulla and extends through the spinal canal down to approximately the first lumbar vertebra. Motor tracts (efferent pathways) continue from the brain down via the lateral and anterior corticospinal tracts to anterior horn  cells, and then exit via ventral nerve roots. Sensory information­ (afferent pathways) enters via dorsal nerve roots. travels up the dorsal columns (proprioception and fine touch) or the spinothalamic tract (pain and temperature) and into the brain stem. Paired nerves.exit the spinal cord at each level. There are 31 pairs: 8 cervical 12 thoracic, 5 lumbar, 5 sacral, and I coccygeal
The dorsal and ventral nerve roots at each level fuse to form motor-sensory spinal nerves and spread through the body provide innervation to muscles and sensory organs The C5-Tl spinal nerves intersect in the brachial plexus and divide to form the main nerve branches to the arm, including the median, ulnar, and radial nerves. The L2-S4 spinal nerves intersect in the Lumbosacral plexus and divide to form the main nerve branches to the leg, in­cluding the common peroneal, tibial. and femoral nerves.
The principal motor tract is the corticospinal tract. It is a two­  neuron path, with an upper motor neuron and a lower motor neuron. upper motor neuron cell body is in the motor strip of the cerebral cortex: The axon travels through the internal capsule to the brain stem. decussates at the brain stem-spinal cord junction, and travels down  the contralateral corticospinal tract to the lower motor neuron
  in the anterior horn at the appropriate level. The lower motor neuron then travels via peripheral nerves to its target muscle. Damage upper motor neurons results in hyperreflexia and mild atrophy. damage to lower motor neurons results in flaccidity and significant atrophy The two major sensory tracts are three-neuron paths. The fine and proprioception signals ascend ipsilaterally via the dorsal column. synapse and decussate in the lower medulla. travel up the contralateral medial lemniscus to the second synapse in the thala­mus and then ascend to the sensory cortex. The pain and tempera­ture fibers synapse in the dorsal hom of the spinal cord at their entry decussate, and travel up the contralateral spinothalamic tracts to the thalamus. The second synapse occurs in the thalamus, and the output ascends to the sensory cortex.
the nervous system is composed of the somatic nervous system.and the autonomic nervous system (ANS). The motor and sensory tracts described so far compose the former. The latter carries messages for homeostasis and visceral regulation from the central ner­vous system (CNS) to target structures such as arteries, veins, the sweat glands, and the digestive tract.  CNS control of the ANS particularly from the hypothalamus and the nucleus of the trac­tus solitarius, The ANS is divided into the sympathetic, parasympathetic­ and enteric systems. The sympathetic system drives the fight or flight" response, and uses epinephrine to increase heart rate
 blood pressure, blood glucose, and temperature, and to dilate the pupils. It arises from the thoracolumbar spinal segments. The parasympathetic system promotes the "rest and digest" state, and uses acetylcholine to maintain basal metabolic function under non­ stressful circumstances. It arises from cranial nerves 11l, V11, IX,and X. and from the second to fourth sacral segments. The enteric nervous system controls the complex synchronization of the diges­tive tract, especially the pancreas, gallbladder, and small and large bowels. It can run autonomously, but is under the regulation of the sympathetic and parasympathetic systems.

tags:Neurosurgery,anatomy,introduction