Brain and spinal cord

If the rostral part of the neural tube does not close (open Neuroporus rostralis), the regular development of the three brain vesicles will not take place. Only a diffuse cluster of neural tissue is formed due to misdirected induction processes. The absence of brain development also results in an improper development of the skull. A facial skull is formed, but the brain and neurocranium are absent (anencephaly ). This developmental malformation is always fatal.

The term encephalocele (hernia cerebri , cerebral hernia, outer brain prolapse, cranium bifidum) summarises defective developmental malformations with a median gap of the skull (at the root of the nose, or the forehead, cranial base, or occiput) ( Fig. a ). Protruding from this gap can be parts of the meninges ( meningocele , Fig. b ), or the brain ( meningoencephalocele , Fig. c ) without involvement of the cerebrospinal fluid spaces ( encephalocele, or d) including parts of the brain ventricles ( encephalocystocele, Fig. d , meningohydroencephalocele ).

Head of a newborn with an extensive herniation in the occipital region. The upper red circle marks the defect in the area of the small fontanelle, the lower red circle indicates the defect in the area of the Foramen magnum.

The hernial sac of a meningocele is formed by the skin and meninges and is filled with cerebrospinal fluid.

The hernial sac of a meningoencephalocele contains parts of the cerebellum and is covered by the meninges and skin.

The hernial sac of this encephalocystocele is formed by parts of the Lobus occipitalis and part of the posterior horn of the lateral ventricle.

Spina bifida is a congenital cleft formation of the spine and the spinal cord caused by teratogenic substances (e. g. alcohol, medication) or the failed induction of the Chorda dorsalis.

In the case of a Spina bifida occulta ( Fig. a ) only the vertebral arches are affected. A vertebral cleft usually results from the failed fusion of one or two vertebrae. Hairy and strongly pigmented skin often covers the area of the defect. There are usually no clinical symptoms.

In the case of a Spina bifida cystica ( Fig. b ), the incomplete development of several adjacent vertebrae leaves a gap through which the meninges covering the spinal cord protrude cyst-like into the defect (meningocele). If the cyst also contains spinal cord and nerve tissue it is considered a meningomyelocele (usually associated with deficits).

A Spina bifida aperta (rhachischisis , myeloschisis , myelocele ; Fig. c ) is the most severe form of a cleft disorder of the vertebral arches and is combined with the inability of the neural folds to fuse. The undifferentiated neural plate is not covered by skin and lies fully exposed on the back. Newborns affected by such defects usually die shortly after birth. If the defect extends to the rostral end of the neural groove, the primordial brain does not develop (anencephaly).

The clinical neurological examination includes a physical examination and the taking of a medical history to obtain information in particular on previous neurological diseases, cranial-cerebral trauma, congenital or familial neurological disorders, risk factors and autonomic functions. This is complemented by taking a symptom-focused history and specific diagnostic techniques to evaluate the cranial nerves and their corresponding functional systems. In addition, the physician should try a preliminary assessment of the patient's consciousness, orientation in space and time, memory function, concentration and basic mood. Disorders of the consciousness are clinically divided into somnolence (abnormal sleepiness but easy to wake up, delayed reaction to verbal communication, immediate response to pain stimuli), sopor (abnormally deep sleepiness and difficult to wake up, delayed but targeted defensive reaction to pain stimuli), and coma (cannot be woken up by external stimuli). A quantitative assessment of impaired states of consciousness, e. g. within the context of a follow-up, can be attained with the Glasgow coma scale . The severity of a consciousness disorder is quantitatively evaluated by testing the patient's spontaneous activity, and his or her response to verbal requests and pain stimuli, and scoring these reactions with points. Disorientation, confusion and perception disorders (e. g. in the context of an alcoholic or drug delirium) can lead to substantial disturbance of consciousness.

Atrophy of the brain develops with advanced age. This is associated with a widening of the sulci and a narrowing of the gyri. However, the decreasing memory function which accompanies advanced age is not directly linked to this atrophy of the brain, but is caused above all by a shorter duration of the deep sleep phases. With ageing, the proportion of deep sleep will diminish significantly. Up to the 26 ^th year of life, 19 % of total sleep duration is spent in deep sleep phases. Between 36 and 50 years of life this percentage drops to 3 %. Studies have shown that this correlates to significant decreases in memory function.

The developmental failure of the primordial structure (agenesis) of the Corpus callosum is, with three to seven cases per 1,000 births, a relatively common malformation in humans. It can have a wide range of causes and may be associated with absent or underdeveloped connections between the left and right hemispheres, without inevitably leading to changes in behaviour. The clinical signs and symptoms depend largely on the cause. It often presents with neuropsychiatric deficits and difficulties in problem-solving behaviour, in the understanding of language and grammar, or in the verbal description of emotions (alexithymia).

Although the neurosurgical resection of the Corpus callosum (callosotomy ) is a treatment option in patients with therapy-resistant epilepsy, it is only practised in exceptional cases. In patients who have undergone this treatment (split-brain patients ) , the information processed in the right half of the brain can no longer be transmitted to the left dominant hemisphere and thereby to the cortical language centres. They can recognise and also describe such information, but are not able to name it precisely.

If a cerebrocranial trauma is accompanied by rupture of the dura mater and the arachnoid mater, e. g. in the area of the nose or ear, this can lead to a fistula of cerebrospinal fluid (CSF fistula ) . This means that cerebrospinal fluid runs out of the nose (rhinoliquorrhoea) or out of the ear (otoliquorrhoea ). To test for the presence of a CSF fistula, a small amount of the fluid is collected to determine its content of glycoprotein β ₂ -transferrin, as this isoform only occurs in the CSF.

Epidural anaesthesia (epidural) is a standard anaesthetic method. After the insertion of a cannula into the epidural space (without penetrating the dura), local anaesthetics can be injected. These anaesthetics act on the spinal roots and spinal ganglia. The epidural is used for the regional elimination of pain, for example in obstetrics, when surgical procedures cannot or do not need to be conducted under general anaesthesia.

Meningiomas are slow-growing, usually benign intracranial tumours. They develop predominantly in the area of the PACCHIONIAN granulations (Granulationes arachnoideae), along the Falx cerebri, in the area of the sphenoidal wings, and in the olfactory groove. They mostly originate from mesothelial cells in the arachnoid mater. Initially, they often remain unnoticed because the surrounding tissue can adapt to the tumour growth rate. So they can achieve a significant size before causing symptoms, e. g. a sudden seizure or increasing headaches. If a surgical resection is possible, the prognosis is very good.

In contrast to the brain and spinal cord, the meninges are extremely well innervated and therefore very pain-sensitive. This is particularly apparent in patients with meningitis, who suffer from severe headaches, accompanied by stiffness of the neck and overextension of the spine (meningismus ). A suspected meningismus can be diagnosed with two tests:

(1) If the head of a supine patient is passively bent forward, and this leads to a reflexive flexion of the legs for pain relief (decompression of the meninges), the BRUDZINSKI's sign is positive.

(2) For a positive KERNIG's sign , the passive lifting of the straightened leg triggers an active flexion of the knee joint due to irritation of the meninges.

Due to their blood-CSF barrier instead of a blood-brain barrier, the circumventricular organs serve as pharmacological access routes. In the case of fever, for example, acetylsalicylic acid (ASA) has an antipyretic action as inhibitor of cyclooxygenase by reducing the production of prostaglandin. In the case of fever, the temperature-sensitive neurons of the Organum vasculosum laminae terminalis have a reduced sensitivity for intrinsic prostaglandins. These neurons normally initiate cooling mechanisms, which in the case of fever only function to a minor extent or not at all. By reducing the prostaglandin formation, ASA can therefore increase the sensitivity of neurons. As a result, the downregulation of the set-point caused by the fever is readjusted to the standard value – and the high temperature/fever is lowered. Central vomiting (emesis), e. g. due to opioids, can be treated with neuroleptic drugs, which bind to dopamine receptors in the Area postrema and thus have an antiemetic effect.

Obstructions of CSF drainage ( Fig. a CT scan image) can be caused by tumours, malformations, bleeding or other factors, and due to increased intracranial pressure they can lead to headaches, nausea and a papilloedema ( Fig. c image of ocular fundus). In the case of a blockage in the inner CSF space, a hydrocephalus internus will occur and impaired drainage in the outer CSF or subarachnoid space will lead to a hydrocephalus externus . Hydrocephalus e vacuo is the term for a condition when ventricular size considerably increases because of a loss of brain substance, e. g. as in ALZHEIMER's disease.

The circumventricular organs ( Fig. 12.47 ) lack the blood-brain barrier and are thus capable of monitoring the plasma-blood milieu; as such they are of more interest than at a purely pharmacological level. The Area postrema for example contains numerous dopamine and serotonin receptors. Highly promising anti-emetic effects can be achieved by using dopamine or serotonin antagonists. In addition, the excitability of biochemical receptors in the Area postrema is a protective mechanism for the whole body, for example by centrally triggered vomiting after the ingestion of spoiled food, so that the major part of the potentially harmful substance is eliminated from the body.

Computed tomographic (CT) cross-section of the head of a female patient with impaired CSF drainage ( Fig. a ) due to a narrowing of the Aqueductus mesencephali [aqueduct of SYLVIUS] . The ventricles are significantly enlarged at the expense of the parenchyma of the brain (hydrocephalus ). The patient suffered from massive intellectual deficits and significant gait disorders. For comparison, a CT scan of a healthy person is shown ( Fig. b ).

Ocular fundus, Fundus oculi; left side; anterior view; ophthalmoscopic image of the central area showing a congested Papilla nervi optici due to increased cranial pressure. A congested Papilla nervi optici (optic disc) is visible on the ocular fundus as a clinical sign of an intraventricular neurocytoma WHO grade II. As the N. opticus [II] is surrounded by meninges and fluid, the optic disc bulges in the eyeball.

The cerebral blood flow has great clinical relevance. Lack of oxygen will irreversibly damage brain tissue (ischaemia tolerance ) within a maximum time of 7–10 min. This must be taken into account in the cardiovascular resuscitation of patients in cardiac arrest. The importance of brain circulation is immediately clear when standing up too quickly leads to a blackout, because the brain is momentarily not sufficiently supplied with blood. The same occurs with fainting (syncope ). The brain is not supplied with enough blood, and as a result, the patient drops to the floor. When lying down, the cerebral blood flow improves and the brain functions return.

Vascular changes (extracranial arteriosclerosis: plaques, stenosis, obliteration) are often located in the carotid bifurcation . The Glomus caroticum (not shown in Fig. 12.48 , Fig. 12.158 ) is a paraganglion located in the carotid bifurcation; it contains chemoreceptors, which react to changes of the pH, oxygen and carbon dioxide levels of the blood.

The carotid sinus syndrome is defined as a hypersensitivity of pressure receptors in the carotid sinus and may often be triggered in response to a rotation of the head. This initiates a reflex that strongly lowers the heart rate (vasovagal reflex ) which can result in cardiovascular collapse and cardiac arrest.

Arteriosclerotic changes in vascular walls are relatively common findings at the outlet of the A. carotis interna from the A. carotis communis, as well as in the Pars cavernosa.

More than 90 % of all cerebral aneurysms occur in the basal cerebral vessels of the Circulus arteriosus cerebri [WILLIS] (figure). Most often, the A. communicans anterior (ACA, up to 40 %) and the A. carotis interna are affected. During the surgical removal of an aneurysm in the A. communicans anterior, care must be taken not to sever the A. centralis longa (syn.: A. striata medialis distalis, A. striata longa , A. recurrens, HEUBNER's artery ). This artery is a branch which mostly originates laterally descending from the proximal A2 segment or the distal A1 segment of the A. cerebri anterior ( Fig. 12.63 ) and runs anti-parallel back to the initial segment of the A. cerebri anterior. In addition, care should be taken to avoid the other branches of the A. communicans anterior, as otherwise postoperative disorders of the memory function could occur (syndrome of the A. communicans anterior ).

Normally, ( Fig. a ) blood flows cranially from the aortic arch (caudal) through both arterial systems supplying the brain (black arrows) to reach the circle of WILLIS, Circulus arteriosus cerebri [WILLIS]. A patient with subclavian steal syndrome (b) frequently has a proximal high grade stenosis of the left A. subclavia. Intense physical activity with the left arm results in retrograde (reverse) blood flow in the left A. vertebralis (affected side, red arrows, Fig. b ). This causes the brain to receive less blood (thin arrows, Fig. b ) which may mean dizziness and headaches. The A. subclavia sinistra is usually affected in patients with subclavian steal syndrome.

Most cerebral aneurysms are congenital defects of the Tunica media in the vascular wall at the points where it branches out. Often, aneurysms are associated with other diseases, such as polycystic kidneys or fibromuscular dysplasia. Cerebral aneurysms are usually asymptomatic. However, the pressure of the aneurysmal sac can lead to a cranial nerve compression.

Cerebral aneurysms have a tendency to rupture and are the most frequent cause of subarachnoid bleeding (haemorrhage). In the case of a rupture, sudden severe headaches occur, combined with vomiting and impaired consciousness.

The blood vessels supplying the brain show relatively great variations in their pattern, which correspond to the variability of the supplied areas. Disorders of the blood flow in these ‘atypical’ vessels can therefore lead to stroke symptoms that cannot be explained in terms of the normal ‘textbook’ anatomy. Not without reason do we say: ‘The exception proves the rule.’

One of the most frequent types of cerebral circulatory disorders (ischaemia) in the vertebral arterial system is the so-called WALLENBERG's syndrome (dorsal-lateral Medulla oblongata syndrome ). In this case, an occlusion or impaired blood flow in the A. inferior posterior cerebell i (PICA = posterior inferior cerebellar artery ) causes a broad range of symptoms, including nystagmus, vestibular disorder, dizziness (Nuclei vestibulares, inferior olive), ipsilateral hemiataxia (Pedunculus cerebellaris inferior, cerebellum), contralateral dissociated sensations (Nuclei gracilis et cuneatus, Tractus spinothalamicus), swallowing difficulties, an attack of hiccups (singultus) and dysphonia (Nucleus ambiguus), HORNER's syndrome and a rapid pulse (central sympathetic system and cardiovascular centre in the rostral-ventrolateral Medulla oblongata), as well as respiratory disorders (respiratory centre in the ventrolateral Medulla oblongata with pre-BÖTZINGER complex).

In most cases a stroke is caused by an acute circulation disorder in a smaller or larger brain area supplied by the affected cerebral artery (ischaemia, brainstem infarction (BSI), 80–90 % of cases). Acute bleeding in the brain (intracerebral haemorrhage) accounts for nearly 10 % of all strokes, followed by subarachnoid haemorrhages (approx. 3 %). The first diagnostic measure to confirm or exclude a haemorrhage, ischaemia or a totally different cause of the neurological symptoms, is a CT of the brain. The speed of the CT-imaging makes it the preferred choice over MRI-imaging. With modern equipment, CT scans of the brain can now be obtained in less than half a minute. If the ischaemia is caused by a thrombus, a pharmacological therapy (thrombolysis) can be attempted. The outcome is largely determined by how much time has lapsed since the stroke (‘time is brain’). Many clinical centres therefore have specialised stroke departments (stroke units). For patients with an intracerebral haemorrhage, however, a thrombolysis is contraindicated. The rapid diagnostic evaluation therefore plays a crucial role in stroke treatment.

In the fetal period, all three cerebral arteries are fed by the ipsilateral A. carotis interna. Once the connection of the A. cerebri posterior to the A. vertebrobasilaris arterial system is established, the original (primary) vessel atrophies and becomes the predominantly thin A. communicans posterior . However, in 20 % of the cases this does not happen, so that in adults (just like in the fetus) an A. cerebri posterior persists which is fed by the A. cerebri posterior.

Occlusions in the bifurcation area of the A. cerebri media due to arteriosclerosis or an embolism result in cerebral infarction (stroke , apoplexy) with severe deficits. These include a contralateral, predominantly brachiofacial hemiplegia with hypaesthesia (circumscribed or general decrease of touch and pressure sensations of the skin). If the dominant hemisphere is affected, this results in aphasia (speech disorder), agraphia (inability to write words and text despite having the necessary mobility of the hand, as well as the intellectual ability) and alexia (inability to read). In patients with high blood pressure (hypertension), changes in the walls of cerebral vessels can cause a vascular rupture and bleeding into the cerebral parenchyma (possibly leading to massive bleeding). The basal ganglia in particular are commonly affected by this.

Arteriosclerosis-induced changes in the wall of vessels are often found in the A. carotis interna . Small thrombi emerging from these plaques can cause an occlusion of the A. centralis retinae via the A. ophthalmica, and thus lead to a sudden painless unilateral blindness. If the thrombus dissolves within a short time it is called amaurosis fugax (short-term blindness ). As a frequent sign of cerebral circulatory disorders, it can be a red flag for an impending stroke.

The anterior choroid artery syndrome is caused by circulatory disorders in the area of the A. choroidea anterior and is associated with a triad of symptoms, including motor, sensory and visual dysfunctions: hemiplegia (failure of motor fibres in the Crura cerebri), hemi-sensory disorders (failure of the Crus posterius of the Capsula interna) and hemianopsia (failure of the Tractus opticus and parts of the Radiatio optica). Circulatory disorders of the A. cerebri posterior lead to visual failures, but can also be associated with temporary deficits of memory function (amnesia), as parts of the hippocampal formation are also supplied with blood from here ( Fig. 12.81 ).

The A. vertebralis can be assessed in the so-called vertebral artery triangle (→ Fig. 2.92) between the M. obliquus capitis superior, the M. obliquus capitis inferior and the M. rectus capitis posterior major; with the head bent forward, the blood flow is determined with a DOPPLER ultrasound examination.

In the case of a stroke, very unusual symptoms can develop due to the blood supply to certain regions. So it is possible that, for example, circulatory disorders of the Aa. pontis lead to failures of motor fibre tracts in ventral parts of the pons, which may be associated with an acute paraplegia. As the dorsal parts of the pons are supplied by branches of the A. superior cerebelli, important areas of awareness such as the Formatio reticularis and also the eye movements remain intact. Patients with locked-in syndrome are despite their paraplegia fully conscious without cognitive impairment, but they can only communicate with eye movements and blinking.

As the Aa. centrales anterolaterales branch off the A. cerebri media almost at a right angle, this part is particularly prone to turbulent blood flow and to secondary arteriosclerotic changes. In patients with high blood pressure (hypertension), occlusions can therefore frequently be found at these bifurcations. Occlusions as well as haemorrhages from these blood vessels can lead to tissue necrosis in the nuclear region of the cerebrum (basal ganglia) and the Capsula interna with resulting (contralateral) hemiplegia. Depending on their location, lesions of the nuclei in the cerebrum can cause severe hyperkinetic or hypokinetic disorders (dystonia).

Due to the blood supply in the region of the Gyrus precentralis, circulatory disorders of the A. cerebri anterior are associated predominantly with leg paralysis and circulatory disorders of the A. cerebri media with brachiofacial paralysis. The patient's clinical picture (leg or brachiofacial paralysis) therefore allows conclusions about the affected vessel.

Strokes or haemorrhages in the area of the Capsula interna frequently involve the A. striata longa (A. striata medialis distalis , A. centralis longa, HEUBNER’s artery , A. recurrens) as a branch of the A. cerebri anterior (belonging to the Aa. centrales anteromediales), or to the A. lenticulostriata as a branch of the A. cerebri media (belonging to the Aa. centrales anterolaterales) ( Fig. 12.63 ).