Vascular Disorders
The first set of conditions that we are going to look at involve problems with blood flow. There are two main categories: haemorrhagic and ischaemic. Haemorrhagic ("bleeding") disorders cause an increase in intracranial pressure, and as such can cause some of the generalised symptoms outlined in my last post. Blood in the interstitial fluid may cause vasospasm (vasoconstriction), which is essentially a reflex to protect the brain from further injury, but may lead to ischaemic disorders. In ischaemic disorders, not enough nutrients get to the brain, so ATP-dependent pumps stop working, as outlined in one of my earliest posts for this course. This causes more Na+ to accumulate in cells, which leads to water entering the cells and cerebral oedema. Ischaemic disorders may be caused by problems such as shock or cardiac arrest.
Transient Ischaemic Attacks (TIAs)
One example of an ischaemic disorder is TIAs. TIAs are caused by temporary, localised small occlusions in one of the blood vessels supplying the brain. This can be caused by narrowing due to atherosclerosis, or an embolus (a clot from somewhere else breaking off and travelling around the blood). Symptoms include paresis (muscle weakness), paraesthesia (altered sensation), visual disturbance or transient confusion, which resolve. Despite the patient retaining consciousness and feeling "fine" after some time, care should be taken as TIAs are potential warning signs for stroke.
Cerebrovascular Accidents (CVAs) (a.k.a. Strokes)
CVAs are essentially the extreme version of TIAs. In a CVA, there is complete occlusion of a blood vessel, which causes liquefactive necrosis of the brain tissue that is no longer receiving blood. Risk factors for CVAs include diabetes, hypertension, heart disease, atherosclerosis, contraceptives and smoking. Sometimes the damage can be reduced by anastomoses, such as the Circle of Willis.
There are three main categories of CVAs: occlusion, embolus and haemorrhagic. CVAs caused by gradual occlusion of the arteries, such as by atherosclerosis, tend to be quite gradual, whereas those caused by emboli are more sudden. Haemorrhagic CVAs can be quite damaging due to the resultant increase in intracranial pressure.
Signs and symptoms of stroke include contralateral paresis and paraesthesia, temporary loss of speech, confusion, dizziness, sudden vision loss and sudden headache. Sometimes stroke is not immediately obvious because it happens in "silent" areas of the brain, or areas that don't control really obvious things. Other effects include flaccid paralysis which develops into spastic paralysis, or inflammation that leads to cerebral oedema.
Stroke caused by occlusion and embolus can be treated by "clot-busting" drugs such as tPA, which converts plasminogen to plasmin, which stops formation of a clot (see here for more information on coagulation pathways). Long-term anticoagulants can help prevent further strokes. However, these can be very damaging in haemorrhagic stroke, as they increase the amount of bleeding.
Other drugs that can be helpful are glucocorticoids, which reduce the amount of inflammation, and antihypertensives, especially when hypertension was one of the potential causes of the stroke. Aside from drugs, therapy can also help stroke patients recover. Therapy makes use of brain plasticity, which is basically the ability of the brain to form new connections and adapt.
Aneurysms
Aneurysms are basically parts of the vascular wall that become weak and bulge out. In the brain, these are more likely to happen at bifurcation points (i.e. ares where an artery branches out) around the Circle of Willis, as blood "hits" these points before separating into two directions. These aneurysms are known as "berry" aneurysms because of their shape, and as they enlarge they can put pressure on the optic nerve or other cranial nerves.
One of the major dangers with aneurysms is that they can rupture and spill out their blood, which is intensely irritating to the nerves. A ruptured aneurysm has a poor prognosis, with a mortality rate of over 50%. Rupture can cause vasospasm as a protective reflex (as stated above), which in turn causes increased intracranial pressure. Irritation to nerves can cause photophobia (extreme discomfort when looking at light), intense headache, confusion, slurred speech, nuchal rigidity (stiff neck due to irritation to nerves supplying neck muscles). Treatment involves surgical "clipping," or insertion of a metal ring to block of the bleeding area, but as you can probably guess by the mortality rate, this is far from perfect.
Concussions
A concussion is when there is excessive brain movement that can cause loss of consciousness or amnesia. Physical damage is usually not evident and a patient can appear to recover in 24 hours, but if multiple concussions are incurred, there is a risk of permanent brain damage. A contusion is a concussion in which there is rupture of small blood vessels, leading to bruising of brain tissue.
One risk with concussions is that sometimes the brain doesn't just endure one "knock"- in contrecoup, the brain rebounds off and hits the other side as well, leading to twice the amount of damage.
Haematomas
Haematomas are collections of blood outside of the blood vessels. They can occur anywhere in the body, but since this is a post about neurological conditions, I'm obviously going to focus on the brain. There are several different kinds of haematomas that can occur in the brain.
- Epidural haematomas occur above the dura mater when the meningeal artery tears. Patients with these haematomas are initially fine, but in around an hour they may lose consciousness.
- Subdural haematomas result from tears in veins and can occur in hours (acute) or weeks (subacute). They take longer to appear in the elderly- due to atrophy of the brain, they have more space that they can "fill" before signs of increased intracranial pressure become evident.
- Subarachnoid haemorrhage isn't actually a haematoma, because blood doesn't pool outside of the blood vessels, but I'm going to include it here anyway. This usually occurs due to aneurysm of blood vessels at the base of the brain. Blood mixes with cerebrospinal fluid and is carried off with it, which is why a haematoma does not form.
- Intracerebral haemorrhage, which also isn't a haematoma, can occur due to shearing injuries or hypertension. It can take weeks to months before signs and symptoms become evident.
Traumatic Brain Injury
Many nasty signs and symptoms can occur as a result of traumatic injury:
- Increased intracranial pressure can result, as haemolysis (destruction of blood cells) increases osmotic pressure, which draws fluid into the brain.
- Seizures
- Headache
- Cranial nerves can become impaired, leading to issues with smell, vision, hearing, swallowing and accessory breathing muscles.
- Otorrhoea and rhinorrhoea (CSF coming out of the ear and nose, respectively) can result due to a disruption in the meninges.
- Otorrhagia (blood coming out of the ear) can also occur as a result of the above.
- Fever
Glucocorticoids can be used to keep inflammation down, and prophylactic antibodies can also be used to stop bacteria from crossing the blood-brain barrier, which is likely compromised. Surgery, in which part of the skull is removed until pressure decreases, may also be warranted.
Spinal Cord Injuries
The most vulnerable parts of the body to spinal cord injuries are the neck (whiplash) and lower spine (from falling on your arse). The good news is that while nerves can't regenerate, the axons can, but this might take a long time.
Spinal cord injuries can cause spinal shock, which is a loss of neurological activity below the point of injury. This starts off as flaccid paralysis and a loss of sensation, as well as loss of autonomic control. Cervical injury, which affects the phrenic nerve (which supplies important stuff like the heart and diaphragm), can cause low blood pressure, loss of sweating, poor temperature control and difficulty emptying the bladder and bowels.
If the spinal cord injury only affects half of the spinal cord, you may get ipsilateral paralysis (as lower motor neurons affect ipsilateral organs), contralateral loss of pain and temperature sensations (as the spinothalamic nerves take sensations from contralateral organs) and ipsilateral loss of fine touch (as the dorsal column nerves take sensations from ipsilateral organs).
As you recover from spinal shock, you get some return of reflex activity, but you may develop spastic paralysis. Complications can include decubitus ulcers (i.e. bed sores, due to many patients having to remain immobile), respiratory infections and something nasty called autonomic dysreflexia.
Autonomic dysreflexia is more likely to occur if the spinal cord injury occurred higher up in the spinal cord. It is essentially the triggering of a widespread sympathetic nervous system response to a relatively mild stimulus like pain, a full bladder, full bowels etc. This widespread activation causes vasoconstriction and increased blood pressure. The increased blood pressure may be sensed by baroreceptors, which ultimately cause bradycardia via the vagus nerve (which is usually unaffected).
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