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Atherothrombotic occlusion of vertebral and posterior inferior cerebellar arteries (PICA)

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Ischemic stroke causes in the vertebral and posterior inferior cerebellar arteries (PICA) basin

Vertebral artery coming from the right innominate artery and the left subclavian artery has four anatomical segments:

  • The first segment continues from the beginning of the vertebral artery until it enters the foramens of the transverse process of the cervical vertebra C6 or C5
  • The second is a vertical segment where vertebral artery passes through foramens in the transverse processes of the vertebrae C6-C2
  • The third segment is horizontal, along its length the artery penetrates through the transverse foramen, bending around the arch of the atlant and penetrating the dura mater at the level of the large occipital foramen
  • The fourth segment starts from the point of perforation of the dura mater artery and extends to a confluence with another vertebral artery, where forms basilar artery
Vertebral arteries pass through the foramens of the transverse processes of the cervical vertebrae.

From the fourth segment of the vertebral artery, small penetrating branches emerge, supplying the medial and lateral segments of the medulla with blood, as well as a large branch — the posterior inferior cerebellar artery (PICA). The proximal segments of the PICA supply blood to the lateral sections of the medulla, the distal branches of the medulla are the lower surface of the cerebellum. There are anastomoses between the ascending cervical artery, thyrocervical artery, occipital artery (branch of the external carotid artery) and the second segment of the vertebral artery. In 10% of patients, one of the vertebral arteries is insufficiently developed (atresia of the artery) in order to play an essential role in the blood supply of the brain stem structures.

The junction of the cervical vertebra with the occipital bone is called the craniovertebral junction or transition. This craniovertebral transition is very complicated in its anatomy because consists of bones, joints, ligaments, muscles, fascia, two vertebral arteries and veins. Anatomical variations of the vertebral artery may include a permanent first intersegmental artery, fenestration of the vertebral artery above and below C1 of the cervical vertebra, posterior inferior cerebellar artery (PICA) from the C1-C2 cervical vertebra, and highly ascending vertebral arteries. Foramen with a bony bridge as an arch is an abnormality of C1 of the cervical vertebra. These anomalies are often found in patients with neck deformities.

Multispiral computer angiography - shows vertebral arteries and cervical vertebrae.
Multispiral computer angiography — shows vertebral arteries and cervical vertebrae.

Variation of vascular and bone anomalies is examined in multislice computer angiography with intravenous contrast in patients with any congenital developmental anomalies or acquired diseases, such as:

Predisposition to the development of atherosclerosis with thrombosis has the first and fourth segment of the vertebral artery. Although the atherosclerotic narrowing of the first segment (the beginning of the artery) can be significant, it rarely leads to an ischemic stroke with a brainstem lesion. Collateral blood flow from the opposite vertebral artery or ascending cervical and thyrocervical arteries or from the occipital artery is usually sufficient.

In those cases where there is hypoplasia (atresia) of one vertebral artery and the initial portion of the other vertebral artery has an atherosclerotic lesion, the only possible sources of collateral blood flow remain the ascending cervical, thyroid-cervical and occipital artery or retrograde blood flow from the basilar artery through the posterior communicating. In such circumstances, the blood flow in the vertebral-basilar system is deteriorating and there are transient ischemic attack (TIA). In addition, the possible formation of initial thrombosis of distal basilar and proximal vertebral localization.

By blocking the subclavian artery proximal to (below) the beginning of the vertebral artery exercise for the left hand may lead to a redistribution of blood flow from the vertebrobasilar system to the arteries of the upper limbs that is sometimes accompanied with symptoms of insufficiency of circulation in vertebrobasilar system — subclavian steal syndrome. In rare cases it causes severe ischemia in the vertebrobasilar system of the brain.

Vertebral arteries merge and form the basilar artery.
Posterior inferior cerebellar artery (PICA) arises from the terminal vertebral artery and courses around the lateral medulla to supply it.

Atherosclerotic plaque in the fourth segment of the vertebral artery may be localized proximal to (below) the beginning of the posterior inferior cerebellar artery (PICA), near the beginning of the posterior inferior cerebellar artery (PICA) or distal to it, and also in the confluence of two vertebral arteries and the formation of the basilar artery. When plaque is located proximal to the beginning of the posterior inferior cerebellar artery, the critical degree of narrowing of blood vessels leads to damage of the lateral divisions of the medulla oblongata and the posterior-lower surface of the cerebellum.

Although the lesion of the vessel with atherosclerosis rarely gives a narrowing of the second and third segments of the vertebral artery, these segments are susceptible to developing dissection, fibro-muscular dysplasia and, in rare cases, arterial damage due to the effects of osteophytes and arthritic changes in the holes of the transverse processes of the cervical vertebrae.

Clinical manifestation of atherothrombotic occlusion in the vertebral and posterior inferior cerebellar arteries (PICA) basin

Transient ischemic attacks (TIA), which develop with insufficient blood supply in the basin of the vertebral artery, causes dizziness, numbness on the face of the same name and in opposite extremities, double vision, dysphonia (swelling of the voice), dysphagia (difficulty swallowing) and dysarthria (difficulty speaking pronunciation ). Hemiparesis (weakness of the muscles of the body half) in patients is extremely rare. Such transient ischemic attacks (TIA) are short (up to 10-15 min) and are repeated in the patient many times during the day.

If cerebral infarcts (ischemic strokes) develop, then most often they affect the lateral parts of the medulla with the involvement of the posterior part of the cerebellum (Wallenberg's syndrome) or without it. Its manifestations are listed in the table below. In 80% of patients, Wallenberg's syndrome develops after occlusion of the vertebral artery, and in 20% — in occlusion of the posterior inferior cerebellar artery (PICA). Atherosclerosis with thrombosis, occluding the penetrating medullary branches of the vertebral or posterior inferior cerebellar arteries (PICA), leads to the onset of partial syndromes of ipsilateral lesions of the lateral and median segments of the medulla.

Due to acute posterior inferior cerebellar artery (PICA) related infarction the patient has the following lateral medullary syndrome of Wallenberg:

  • ipsilateral Horner syndrome
  • contralateral loss of pain and temperature sensation in the body
  • ipsilateral facial pain
  • dysphagia, sometimes requiring gastrostomy
  • ipsilateral ataxia
After moving away from the medulla (2), posterior inferior cerebellar artery (PICA) forms a very prominent cranial loop (4), this loop where the PICA curves above the cerebellar tonsils (5).
On this angiogram, after the posterior inferior cerebellar artery (PICA) take-off there's a small caudal loop, followed by a larger cranial (tonsillar) loop (white arrow). Embolization of vascular lesion (cerebellar AVM or aneurysms located at the proximal posterior inferior cerebellar artery), through its PICA feeder, occluding the PICA after this tonsillar loop shouldn't cause the lateral medullary syndrome. Yet may cause cerebellar infarction though, but with a minor risk.

Sometimes there is a syndrome of damage to the median part of the medulla, in which the pyramid of the medulla is involved in the zone of the infarction. The syndrome of involvement of the middle part of the medulla causes contralateral hemiparesis in the upper and lower limbs and does not affect the musculature of the face. When the medial loop and the fibers of the hypoglossal nerve emerging from the medulla are affected, a contralateral decrease in the musculo-articular feeling is noted and ipsilateral paralysis of the tongue muscles.

Cerebellar infarction (ischemic stroke) with concomitant cerebral edema can lead to a sudden stop of breathing due to increased intracranial pressure in the posterior cranial fossa. Drowsiness (hypersomnia), Babinsky's symptom, speech disorder (dysarthria) and bilateral weakness of facial muscles are often absent or found only shortly before the onset of respiratory arrest. Imbalance in walking (ataxia), dizziness, nausea and vomiting can be among the few early symptoms and should raise suspicions about the possibility of developing this complication.

 

Medullary syndrome:

Signs and symptoms
Structures involved
1. Medial medullary syndrome (occlusion of vertebral artery or of branch of vertebral or lower basilar artery)
On side of lesion:
Paralysis with atrophy of half the tongue Ipsilateral twelfth nerve
On side opposite lesion:
Paralysis of arm and leg, sparing face; impaired tactile and proprioceptive sense over half the body Contralateral pyramidal tract and medial lemniscus
2. Lateral medullary syndrome (occlusion of any of five vessels may be responsible — vertebral, posterior inferior cerebellar, superior, middle, or inferior lateral medullary arteries)
On side of lesion:
Pain, numbness, impaired sensation over half the face Descending tract and nucleus fifth nerve
Ataxia of limbs, falling to side of lesion Uncertain — restiform body, cerebellar hemisphere, cerebellar fibers, spinocerebellar tract (?)
Nystagmus, diplopia, oscillopsia, vertigo, nausea, vomiting Vestibular nucleus
Horner’s syndrome (miosis, ptosis, decreased sweating) Descending sympathetic tract
Dysphagia, hoarseness, paralysis of palate, paralysis of vocal cord, diminished gag reflex Issuing fibers ninth and tenth nerves
Loss of taste Nucleus and tractus solitarius
Numbness of ipsilateral arm, trunk, or leg Cuneate and gracile nuclei
Weakness of lower face Genuflected upper motor neuron fibers to ipsilateral facial nucleus
On side opposite lesion:
Impaired pain and thermal sense over half the body, sometimes face Spinothalamic tract
3. Total unilateral medullary syndrome (occlusion of vertebral artery)
Combination of medial and lateral syndromes
4. Lateral pontomedullary syndrome (occlusion of vertebral artery)
Combination of lateral medullary and lateral inferior pontine syndrome
5. Basilar artery syndrome (the syndrome of the lone vertebral artery is equivalent)
A combination of the various brainstem syndromes plus those arising in the posterior cerebral artery distribution
Bilateral long tract signs (sensory and motor; cerebellar and peripheral cranial nerve abnormalities) Bilateral long tract; cerebellar and peripheral cranial nerves
Paralysis or weakness of all extremities, plus all bulbar musculature Corticobulbar and corticospinal tracts bilaterally
Lateral and medial medullary syndromes. Really important structures pass through the lateral medulla: sympathetic fibers, spinothalamic tract, spinal nucleus of the V cranial nerve, nucleus ambiguous of the X cranial nerve, inferior cerebellar peduncle. This area is supplied by the posterior inferior cerebellar artery (PICA).

 

Diagnosis and imaging studies of ischemic stroke in the vertebral and posterior inferior cerebellar arteries (PICA) basin

When transient ischemic attack (TIA) with the clinic of lesions of the lateral divisions of the medulla, it is important to determine the adequacy of the blood flow:

  • in the distal (upper) zone of the vertebral artery basin
  • in the posterior inferior cerebellar artery (PICA)

For the purpose of diagnosis, angiography is prescribed. With computed tomography (CT), you can find an extensive cerebellar infarction in the basin of the posterior inferior cerebellar artery. Magnetic resonance imaging (MRI) enables early detection of cerebellar infarction and, as far as technical improvement, will allow to diagnose the lateral infarction of the medulla oblongata. It has already become possible to visualize the fourth segment of the vertebral artery, if it has blood flow.

On the brain MRI a black arrow shows ischemic stroke in the lateral part of the medulla (Wallenberg syndrome) after the right vertebral artery dissection (white arrow).
MRI of the cervical spine shows the dissection of the right vertebral artery.

Later, using high-field magnetic resonance imaging (MRI with 3 Tesla and more) in the angiography mode of the cerebral vessels it became possible to obtain an image of atherosclerosis with thrombosis in the vertebral and basilar arteries. It is also possible to establish patency or occlusion (blockage) of the vertebral and inferior cerebellar artery.

Magnetic resonance imaging angiography (MRI angiography) of cerebral vessels on a high-field tomograph (3 Tesla) allows the doctor to replace the relatively dangerous and harmful for the patient angiographic study of cerebral blood flow with intravenous contrast in computed tomography (CT).

Multislice computed tomography (3D CT) of the vertebral arteries and the cervical-occipital junction.

 

Treatment of the ischemic stroke in the vertebral and posterior inferior cerebellar arteries (PICA) basin

When treating patients with ischemia or infarction of the brain (cerebellum, medulla) in the basin of the vertebral or posterior inferior cerebellar artery (PICA) there are four important questions:

  • When occluding the vertebral or posterior inferior cerebellar artery, the posterior sections of the cerebellum and sometimes the lateral parts of the medulla may undergo infarction. Developing edema of the cerebellum can be treated with osmotic diuretics (mannitol), but sometimes surgical decompression of the posterior cranial fossa and dissection of the cerebellum are required.
  • In thrombosis of the fourth segment of the vertebral artery, the thrombus can spread into the basilar artery or be the source of embolism in the basilar artery. These emboli are stuck in the upper part of the main artery or in one of its branches. Therefore, in cases of a lateral infarction of the medulla oblongata, symptoms of basilar insufficiency may appear. In such situations, it is strongly recommended that emergency anticoagulant therapy with heparin be prescribed. Some doctors insist on the preventive use of this technique for acute occlusion of the vertebral artery, although there is evidence of the effectiveness of long-term treatment with sodium warfarin.
  • With clinically manifested atherosclerosis of one vertebral artery with concomitant congenital atresia (underdevelopment) or the already formed occlusion of the opposite vertebral artery, may develop ischemia in the basin of the basilar artery and its proximal thrombosis. In such circumstances, immediate anticoagulant therapy with heparin was shown, followed by long-term use of sodium warfarin.
  • In the same cases, but when localizing the clinical symptoms of atherosclerosis with thrombosis in the vertebral artery, proximal (lower) to the posterior inferior cerebellar artery (PICA), an operation is recommended for bypass vascular bypass between the occipital and posterior inferior cerebellar arteries. The effectiveness of this operation has not been proven, and therefore the question of its implementation can be raised only after the treatment of thrombosis with occlusion of the lumen of the vertebral artery with anticoagulants has not yielded results.
Aneurysms located at the proximal posterior inferior cerebellar artery (PICA) may need to be cliped and concomitant bypass. End-to-side anastomosis of the occipital artery to PICA is one bypass option in these cases for lateral medullary syndrome prophilaxy.

 

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