Clinical manifestations

Presentation and course

Onset is sudden and the major symptoms of cerebellar stroke are occipital headache, vertigo, nausea and vomiting, and unsteady gait. A typical feature is the patients inability to stand or walk due to gait and truncal ataxia as well as ipsilateral lateropulsion. Headache is present in about 35% of patients with infarct and 70% of those with hemorrhage. Thunderclap-type headache and migraine-type headache associated with cerebellar infarction have been reported in the literature (16; 32). Dysarthria, often called ataxic dysarthria, dysmetria, and nystagmus are less common signs.

Decreased level of consciousness ranging from lethargy to coma occurs in patients with infarction, often secondary to the development of hydrocephalus, and it usually has a delayed onset, whereas coma is a common presenting sign of cerebellar hemorrhage.

Signs of brainstem infarction may occur in half of the patients (Brennan 1977; 20; 36; 12; 13). The associated brainstem signs depend on the vascular territory affected by ischemia or on direct compression of the brainstem secondary to edema (70; 02; 36).

Posterior inferior cerebellar artery (PICA) infarctions are found in approximately 2% of patients with ischemic stroke and are the most frequent type among all patients with cerebellar infarction. The PICA arises from the vertebral artery and courses transversely and downward along the medulla. The common trunk gives rise to the medial branch (medPICA) and the lateral branch (latPICA). In patients with a medPICA territory infarct, vestibular signs, dizziness, vertigo, truncal ataxia, ipsilateral axial lateropulsion, and nystagmus are the most common signs. In comparison, those patients with an isolated latPICA infarct have dizziness, vertigo, and dysmetria without truncal ataxia or axial lateropulsion (49).

Because the medial branch of PICA participates in the blood supply of the medulla in its rostral region, up to 30% of the PICA distribution infarctions also involve the lateral medulla, resulting in ipsilateral Horner syndrome (due to affectation of the first order neurons), decreased sensation in the ipsilateral trigeminal distribution, and contralateral hypesthesia to pain and temperature in limbs and trunk (37).

By contrast, 10% of patients with a pure lateral medullary infarct have an associated PICA distribution cerebellar infarction (45). Few patients have presented with isolated vertigo when the uvulonodular region of the cerebellum is affected by an occlusion of the medial branch of PICA (19). Bilateral cerebellar infarcts in distribution of PICA are rare and likely caused by occlusion of a unilateral supply to both medPICA territories (35). Some patients with cerebellar infarction in the PICA territory may have cognitive and affective deficits due to impairment of posterior cerebellar function (22).

Anterior inferior cerebellar artery (AICA) infarcts are found in about 0.6% of patients with first-ever stroke (50). The AICA arises from the caudal third of the basilar artery. It supplies a small area of anterior and medial cerebellum, middle cerebellar peduncle, and flocculus. Its proximal branches supply the nuclei of cranial nerves V, VII, and VIII, the roots of the sixth and eighth cranial nerves, and the spinothalamic tract. When PICA is hypoplastic, the ipsilateral AICA usually becomes large and supplies the whole antero-inferior cerebellum.

The AICA classic and most frequent syndrome is seen in 30% of cases. This syndrome is characterized by ipsilateral facial palsy, hearing loss, tinnitus, trigeminal sensory loss, Horner syndrome, and limb dysmetria with contralateral pain, and temperature sensory loss in limbs and trunk. AICA territory infarct is the most common cause of acute onset combined audio and vestibular dysfunction. Furthermore, it is rare for isolated vestibular or cochlear loss to be due a vascular etiology (44). Of patients with AICA syndrome, 30% present with prodromal episodes of acute auditory disturbance including transient or prolonged (up to 10 days) hearing loss with or without tinnitus (55). These prodromal symptoms might contribute to misdiagnosis as Ménière disease (71).

Sudden onset of not only unilateral deafness but also bilateral deafness due to AICA occlusion has also been reported (56; 30; 39). On occasion, patients may have lateral gaze palsy. This syndrome occurs due to the involvement of the dorsolateral region of the lower pons. Infarcts in this distribution often herald a basilar artery occlusion. In fact, 20% of cases patients are comatose and quadriplegic on presentation (02; 05).

The superior cerebellar artery (SCA) arises from the rostral basilar artery. There are two main branches of SCA, the medial SCA and the lateral SCA. The medial SCA supplies the dorsomedial area of SCA territory including the vermis, whereas the lateral SCA supplies the anterolateral area of SCA territory that includes the lateral and anterior aspects of the anterior cerebellum. Small penetrating branches of the SCA also supply the laterotegmental portion of the rostral pons including the superior cerebellar peduncle, spinothalamic tract, lateral lemniscus, corticotegmental tract, descending sympathetic tract, and the root of the contralateral fourth cranial nerve. Because of the distal location of its branching point from the basilar artery, its proximity to the posterior cerebellar artery (PCA), and the embolic nature typical of its occlusion, infarcts in the SCA distribution are frequently associated with infarcts in the midbrain, diencephalon, and occipital temporal regions. Consequently, frequent signs include coma, quadriplegia, deconjugated gaze, diplopia, transcortical motor aphasia, visual field deficits, and confusion (03; 02).

The most common SCA syndrome arises from the involvement of the lateral branch and results in prominent limb ataxia (03; 49b; 77). In contrast, patients with an infarct in the territory of medial branch of SCA usually present with prominent gait ataxia and cerebellar or ataxic dysarthria (77).

A course complicated by obstructive hydrocephalus occurs in 10% to 25% of cases of cerebellar infarction. The factors associated with this clinical course are involvement of more than one third of the cerebellar hemisphere; vascular occlusion at the ostia of the SCA and PICA with no collateral flow; vasogenic edema secondary to reperfusion; and a massive SCA distribution infarct with a more medial location that favors the development of hydrocephalus such as the vermis (80; 62; 02; 37).

Deterioration following the edema formation in patients with infarction may be secondary to compression of the brainstem, hydrocephalus, extension of the ischemia to the brainstem, or a combination (80; 62). Typically, clinical deterioration occurs in a mean time of 5 days from onset (10 hours to 10 days) and the initial sign is decreased level of consciousness (58; 80).

Direct brainstem compression often leads to horizontal gaze palsy, ipsilateral facial palsy and ipsilateral hemiparesis secondary to contralateral pyramidal tract compression against the clivus (28). Some patients may develop hyperventilation, upward gaze palsy, and nonreactive pinpoint pupils indicating an upward transtentorial herniation of the cerebellum with compression of the dorsal midbrain. Other patients develop tonsillar herniation manifested by neck stiffness, arrhythmias and ataxic breathing. Despite the clinical signs, it is difficult to ascertain the mechanism of deterioration on pure clinical grounds.

Of patients with cerebellar hemorrhage, 10% to 20% present with altered level of consciousness (70; 20). For those non-comatose on admission, deterioration can be predicted with limited success, and the clinical course can be unpredictable even in patients with a normal level of consciousness (01).

Patients at higher risk of deterioration are those that present with a systolic blood pressure higher than 200 mmHg, absent corneal reflexes, impaired oculocephalic responses, vermian hemorrhage or hemispheric hemorrhage extending to the vermis, and patients with early hydrocephalus. The risk of deterioration is low in patients with no evidence of brainstem distortion, upward herniation, or compression of the fourth ventricle on initial imaging (78; 79).

Sinus bradycardia or a pronounced sinus arrhythmia is associated with compression of the brainstem and may be an early sign. Deterioration is most commonly caused by brainstem compression than hydrocephalus.

Prognosis and complications

Prognosis in cerebellar infarction is generally favorable. Overall, about 62% of patients survive with no deficits or minor deficits, 31% with moderate to severe deficits, and 7% die (62; 37; 14; 13). In patients with the course complicated by hydrocephalus, a poor outcome is seen in those older than 60 years, with brainstem signs on presentation, and in those in coma with extensor posturing and arrhythmias on admission (31).

The prognosis is good in patients with PICA syndrome except for those with multiple brain stem lesions (49). Some have described a worse functional outcome in patients with a SCA distribution infarction (83). Coexisting white matter changes may be associated with poor functional outcome in patients with cerebellar infarction, regardless of infarct volume and topography of infarction (25).

The mortality of cerebellar hemorrhage depends on the level of consciousness on presentation, ie, as low as 5% in those conscious patients who underwent surgical decompression to close to 100% in those comatose on admission (70; 20; 29; 84; 01). Factors associated with poor prognosis include age older than 70 years, Glasgow coma score less than or equal to 8, absent corneal and oculocephalic reflexes, complete effacement of the fourth ventricle, and hydrocephalus on presentation (64; 29; 72). The functional outcome after cerebellar hemorrhage is worse than ischemic cerebellar stroke, as 57% of survivors have a modified Rankin scale score of greater than 2 at 30 days (72).

Clinical vignette

A 42-year-old woman complained of hearing a buzzing noise of sudden onset while at work. Over the following minutes, she developed dizziness, occipital headache, blurred vision and noted difficulty walking, as she needed support to remain steady. As her symptoms quickly progressed, she developed nausea and vomiting and became unable to stand. She was recently diagnosed with hypertension and was taking losartan. She also was on oral contraceptives. She denied history of migraine and did not smoke.

On examination, she was awake and oriented and had normal speech. She looked uncomfortable and kept her eyes closed as to avoid blurred vision. Her gaze was conjugate, and she had horizontal nystagmus. Her eyes movements showed saccadic smooth pursuit and testing exacerbated her nausea. She had a right Horner syndrome and a decreased touch and temperature on the right side of her face. Her strength was normal. She had significant dysmetria in the right arm and leg. She also had decreased touch and temperature in the left side of her chest and her left limbs. Her reflexes were symmetric and normal; the plantar response was flexor bilaterally.

Her diagnostic work-up that included a transesophageal echo, MRA of the neck vessels and vertebral artery origin, and testing for protein C, protein S, antithrombin III deficiency, and antiphospholipid antibody was normal. MRI of the brain showed a cerebellar infarct in the right superior cerebellar artery distribution involving the superior aspect of the cerebellar hemisphere and vermis. There was a small infarct in the posterolateral aspect of the pons. The MRA of the head showed absent bilateral SCAs with the rest of the intracranial circulation appearing normal. Her symptoms improved and 2 weeks later she was normal except for some residual clumsiness of her right hand and decreased touch in the left arm.

Biological basis

Etiology and pathogenesis

Embolism from arterial or cardiac source and intracranial atherosclerosis are the main culprits (12). Hypertension is the most common cause of cerebellar hemorrhage (70; Brennan 1977; 20; 36).

The mechanisms of cerebellar infarction are cardiac embolism in 30%, artery-artery embolism in about 20%, large artery atherothrombosis in 23%, and the rest are either other or unknown causes (37; 04; 14; 12).

The mechanisms differ if one considers the vascular territory affected; those in the PICA distribution are secondary to embolism in more than 50% of the cases (cardiac or artery-artery), and local atherosclerosis is responsible for 16% to 41% of cases (09; 37; 04; 12; 51). Infarcts in the AICA territory are most commonly caused by atherosclerotic occlusive disease of the basilar artery (02; 05; 12; 50). Finally, more than 50% of infarcts in the SCA distribution are due to cardiac or artery-artery embolism (38; 62; 04; 12; 49).

Hemorrhages are directly linked to hypertension in 50% to 60% of cases. Vascular malformations, including arteriovenous and cavernous malformations, may be found in as many as 18% of cases. In 10% to 30% of cases the cause remains unknown (Brennan 1977; 20; 36).

Epidemiology

The prevalence of cerebellar infarction in the population is not known. Cerebellar infarcts are more frequent than hemorrhages; about 80% versus 20% ± 5% in autopsy and CT scan series (19; 76; 02). Cerebellar infarcts account for 1.5% to 4.9% of ischemic strokes in autopsy series and 1.9% of first strokes in a large stroke registry (80; 10; 02).

The disease is more frequent in men than in women (2:1) and the mean age is 65 years, although half of the patients are 60 to 80 years (02). PICA distribution infarcts are the most common type (56%) among all patients with cerebellar ischemic stroke (49). The PICA and SCA vascular territories are involved in cerebellar infarction occurring in 84% of patients (12). Cerebellar hemorrhage was reported in 0.38% of all autopsies and account for 5% to 13% of intracerebral hemorrhages (68)

Prevention

Primary stroke prevention must be focused on risk factor control, namely control of hypertension, hyperlipidemia, and diabetes. Weight loss, smoking cessation, and cessation of substance abuse are other important prevention measures.

Antiplatelet agents should be used in most patients unless there is an absolute indication for anticoagulation, such as atrial fibrillation with a high CHA2DS2-VASc score. High-intensity statin (atorvastatin or rosuvastatin) therapy is indicated in all patients with hyperlipidemia and high LDL levels with other risk factors.

Although extracranial vertebral or intracranial vertebral basilar artery angioplasty with or without stent placement for high-grade stenosis has been used for stroke prevention, there is no evidence from randomized clinical trials to support their use in routine clinical practice.

Because hypertension is the main cause of cerebellar hemorrhage, the mainstay for prevention is blood pressure control.

Differential diagnosis

Confusing conditions

The sudden onset of symptoms limits the differential diagnosis beyond cerebellar ischemic stroke and cerebellar hemorrhage.

A frequent cerebellar stroke mimic is peripheral vestibular disease; however, the patient’s inability to stand or walk should raise the level of suspicion. The bedside head impulse or head thrust test of vestibular function can easily be done during physical examination. During this test, the examiner turns the patient’s head quickly while the patient’s eyes fixate on an object. Normally, an individual can undergo a fast head turn while maintaining fixation. In an abnormal test, the individual will have to make a corrective saccade back to the object after the fast turn as the eyes will follow the head movement. This abnormality is the result of diminished input from the ipsilateral vestibular apparatus, thus, indicating a peripheral disorder. This vestibulo–ocular reflex (VOR) test usually helps to distinguish a peripheral cause, for example vestibular neuritis from a central cause—particularly cerebellar stroke (33; 15; 69).

Small strokes affecting the central vestibular projections can present with acute vestibular syndrome, and up to half of these patients will have a negative MRI up to 48 hours after onset (75; 21). Clinical exam techniques such as the HINTS “plus” exam has a reported sensitivity of 100% in the setting of an acute vestibular syndrome with at least one stroke risk factor (75).

A posterior fossa tumor could be considered in patients with a protracted course who experience delayed neurologic deterioration following headache. Cerebellar infarction is sometimes misdiagnosed, particularly in younger patients, because it might not be considered by the physician (08).

Diagnostic workup

Cerebellar hemorrhages are easily seen by CT scan. The findings associated with clinical worsening and outcome include location (hemispheric vs. vermian), presence of hydrocephalus, and compression of the quadrigeminal and ambien cisterns; when these findings are present, they indicate a tight posterior fossa (88).

A hematoma greater than 3 cm influences clinical deterioration with the needed consideration of early surgical evacuation and decompression with a suboccipital craniectomy (59).

MRI brain may be useful in identifying underlying tumors or vascular malformations. CT angiography can be useful in identifying any underlying vascular malformations but may be negative in the acute setting due to the presence of the hematoma. Digital subtraction angiography is the test of choice if suspicion for a vascular malformation as the cause of the hemorrhage is high.

Although a CT scan is often negative in the acute setting after an infarct, it is highly useful in identifying features of a tight posterior fossa as it can be seen in patients with clinical deterioration secondary to massive cerebellar edema caused by an infarction.

Beam hardening artifact from dense petrous bone may result in poor resolution of the posterior fossa on CT. Therefore, MRI can be useful in establishing the diagnosis of infarction and estimating the size of the stroke burden. In patients with hemorrhage, MRI may help to identify an underlying tumor or vascular malformation.

Acutely, a CT angiography may help in establishing the patency of the large intracranial vessels. A digital subtraction angiography is the gold standard for vessel imaging, may be necessary if there is a high clinical suspicion for basilar artery occlusion, and may influence treatment decisions.

The key point of the work up is to ascertain the cause of the infarct to guide secondary prevention. CTA or MRA of the intracranial and extracranial vessels will be useful in the search for large vessel atherosclerosis or dissections.

EKG is useful in identifying atrial fibrillation or other arrhythmias, which will guide secondary prevention. Nearly 10% of patients presenting with a stroke or transient ischemic attack are newly diagnosed with atrial fibrillation during their hospital admission (74). If suspicion for embolic stroke is high (embolic stroke of unknown source, ESUS), or in cases of cryptogenic strokes and transient ischemic attack, extended cardiac monitors should be prescribed on discharge to look for paroxysmal atrial fibrillation. Outpatient telemetry monitoring has been shown to identify paroxysmal atrial fibrillation in approximately 20% patients over 3 weeks of monitoring (82; 74; 67). Current AHA guidelines recommend approximately 30 days of monitoring within 6 months of cryptogenic stroke or transient ischemic attack (42).

Transthoracic echocardiogram is a noninvasive study that may establish the presence of potential cardiac sources of embolism, such as intracardiac thrombus, right to left shunts, or cardiac tumors (myxoma, fibroelastoma). Transcranial doppler is another noninvasive sonographic procedure that may be used to identify right to left shunts, such as a patent foramen ovale. Transcranial doppler is more sensitive but less specific for the detection of patent foramen ovale than transesophageal echocardiogram (40). Transcranial doppler may also be used to identify ongoing embolization to the posterior fossa by insonating the basilar artery and monitoring for microembolic signals over a period of time (17). If an intracardiac source is still suspected and the above tests are nondiagnostic, a transesophageal echo (TEE) may detect a cardiac source of embolism in nearly 40% of patients with an unrevealing TTE (18). Cardiac CT is another useful alternate modality to detect cardiac sources of embolism in patients with negative TTE.

Strokes in young. In cases of cerebellar stroke in young patients under the age of 45, an extensive hypercoagulable work-up should be pursued, including, but not limited to, protein C, protein S, antithrombin III, and antiphospholipid antibodies (11). Procoagulant tests can be abnormal in the acute phase of stroke or hemorrhage, and they can be altered by inpatient use of anticoagulants; therefore, the hematologic work-up should be repeated during outpatient follow-up. Other causes of hypercoagulability, such as estrogen-containing over-the-counter medications, may be investigated in young patients with a patent foramen ovale and no other risk factors.

Management

Cerebellar infarction

Acute management

Intravenous thrombolysis. Intravenous thrombolysis with IV tissue plasminogen activator (tPA), either alteplase or tenecteplase (TNK), remains the mainstay of treatment for acute ischemic cerebellar infarctions in patients that meet criteria for their administration.

Multiple trials, including ATTEST, NOR-TEST, EXTEND-IA TNK, TAAIS, and a few others, have looked at the safety and efficacy of tenecteplase for acute ischemic stroke in place of alteplase. Tenecteplase has been shown to have the same safety profile with more ease of administration and longer half-life. A meta-analysis of some of these trials have shown a trend of superior early recanalization in large-vessel occlusions and noninferiority with regards to outcomes compared to alteplase, but more studies are ongoing (86). A meta-analysis by Ma and colleagues looked at 14 studies and showed that tenecteplase was as safe and effective as alteplase for acute ischemic stroke and might provide more benefit with regards to early neurologic recovery and a higher incidence of successful recanalization (61).

Mechanical thrombectomy. Mechanical revascularization is an exciting new treatment modality in the acute management of anterior circulation strokes. Mechanical thrombectomy for basilar strokes has not been similarly investigated and is reflected in AHA guidelines, which state that basilar occlusions may be considered for mechanical thrombectomy within 6-hours (level 2b evidence) compared to level 1 evidence for anterior circulation large-vessel occlusions (26).

A meta-analysis of posterior circulation clot removal found a favorable outcome (MRS 0 to 2) in nearly 40% and a mortality rate of 30% on 3-month follow-up (53). Distal basilar artery occlusion, good collateral circulation, shorter time to recanalization, and successful recanalization were associated with improved clinical outcomes on follow-up (48; 24; 53; 87).

Both, the BEST trial as well as the BASICS randomized controlled trial failed to show a benefit of endovascular thrombectomy over medical management (IV tPA), with a non-significantly higher symptomatic intracerebral hemorrhage rate in the endovascular thrombectomy group (60; 54).

However, the ATTENTION trial (012 hours from symptom onset) and the BAOCHE trial (624 hours from symptom onset) presented at the 2022 European Stroke Conference showed improved outcomes as well as a mortality benefit of endovascular thrombectomy for basilar artery occlusion (34; 63; 81).

The effectiveness of endovascular thrombectomy for other regions of posterior circulation strokes, including posterior cerebral artery occlusions and vertebral artery occlusions, needs more studies to be confirmed.

Blood pressure control. Blood pressure targets in the first 24 hours after acute infarct vary depending on whether the patient has had any intervention.

Long-term blood pressure management should follow the American Heart Association recommendations, which call for treatment if the mean arterial pressure is greater than 130 mmHg.

ICU care. Whether a patient needs close neuromonitoring in an ICU, preferably a neuro ICU, after a posterior territory stroke is an important, and not a straightforward, decision to be made. Posterior circulation strokes can often show delayed deterioration, as late as 10 days after stroke.

All IV tPA and mechanical thrombectomy patients should be monitored for complications or deterioration in an ICU or stroke unit for at least 24 hours after treatment.

The following features are associated with delayed worsening:

(1) Decreased level of consciousness; territorial infarction involving PICA, SCA, or both vascular distributions.

(2) Involvement of more than 30% of the cerebellar hemisphere.

(3) Compression of the fourth ventricle or the quadrigeminal cistern.

(4) Hydrocephalus (29; 72).

Therefore, patients at high risk for decline or those that undergo surgery early should be monitored closely in an ICU that can provide neuroscience specialized care.

Surgical intervention. As swelling from cerebellar infarctions can result in obstructive hydrocephalus, brainstem compression, and tonsillar herniation, performing a suboccipital craniotomy is the guideline recommendation by the AHA in the setting of neurologic decline despite maximal medical management (26). Current guidelines recommend suboccipital craniectomy with or without brain resection in patients with decreased alertness and compression of the brainstem.

Long-term management

Early focus on rehab. Physical therapy, occupational therapy, and speech therapy are essential to have the best chance of recovery of function. Percutaneous gastrostomy tubes may be needed to provide adequate nutrition and oral medications in the acute phase of recovery if the patient is unable to safely swallow.

Secondary stroke prevention. Antiplatelet therapy with high-intensity statin along with risk factor control form the cornerstone of secondary stroke prevention. For small- to moderate-sized strokes, treatment with dual antiplatelet therapy (DAPT) for 3 weeks followed by monotherapy with aspirin is recommended. In presence of intracranial stenosis, DAPT for 3 months is recommended.

Anticoagulation in place of antiplatelet therapy with warfarin or direct oral anticoagulants, such as apixaban or rivaroxaban, should be considered in patients with nonvalvular atrial fibrillation or overt hypercoagulable states if there is no contraindication.

Blood pressure control, use of high-intensity statins, and optimum blood glucose control in diabetics are essential. Smoking cessation and lifestyle modifications, including weight loss and healthy diet, are extremely important as well.

Cerebellar hemorrhage

Acute management

Blood pressure control. In the setting of cerebellar hemorrhage, initiation of blood pressure lowering medication is indicated. The ideal blood pressure target following intracranial hemorrhage is still widely debated, with some advocating systolic blood pressure less than or equal 140 to 160 mmHg.

The following are the recommended agents: labetalol 20 mg to 40 mg intravenously repeated as needed not to exceed 300 mg in 24 hours; nicardipine in a continuous intravenous drip at a starting dose of 2.5 mg/hour and titrating to a maximum dose of 15 mg/hour; nitroprusside 0.5 micrograms/minute to 10 micrograms/minute intravenously; and clevidipine 1 to 2 mg/hour intravenously and titrating to a maximum dose of 21 mg/hour. It is advised to aim for a 125% reduction of mean arterial pressure within the first 24 hours (73).

ICU care. Most patients with cerebellar hemorrhage should be admitted to an ICU and preferably to a neurocritical care unit due to the high likelihood of deterioration.

Patients will require intubation with ventilatory support once their alertness is impaired and they cannot protect their airway.

Useful indicators include Glasgow coma score less than 8 and bulbar dysfunction. These patients will benefit from pressure support ventilation, as most of them will have spontaneous breathing patterns. When ataxic respirations or even apnea follow progressive deterioration, or when hyperventilation is required to control intracranial pressure, then modes of ventilation that control the rate and tidal volume may be required (89).

Management of cerebral edema. For those patients with clinical deterioration due to cerebral edema, some temporizing measures such as hyperventilation and the use of mannitol 1 gm/kg or hypertonic saline intravenously are indicated while deciding on a definite treatment.

Surgical intervention. The mainstay of treatment in those patients with decreased alertness and compression of the brainstem is the suboccipital craniectomy with or without brain resection (90). Some authors have advocated ventriculostomy as an initial measure when hydrocephalus is present; however, if there is no improvement in the level of consciousness promptly following the ventriculostomy, patients should undergo a surgical decompression.

Forty percent to 50% of patients with cerebellar hemorrhage will require surgical decompression. As in the case of infarction, the suboccipital craniectomy is indicated when there is impairment of consciousness associated with a hemorrhage larger than 3 cm, a tight posterior fossa and hydrocephalus. Ventriculostomy can be used when hydrocephalus is the predominant feature, but surgical evacuation is often pursued shortly thereafter if no clinical improvement occurs after the ventriculostomy has been placed. Ventriculostomy can be used when hydrocephalus is the predominant feature, but the surgical evacuation should follow shortly thereafter if no clinical improvement occurs after the ventriculostomy has been placed (47; 64; 89).

However, there remains several questions for surgical management of both hemorrhagic and ischemic cerebellar strokes including optimal timing for surgery, use of CSF diversion with surgery or surgery alone, and surgical approach (eg, decompression alone vs. removal of cerebellar tissue vs. clot removal) that require further investigation.

Cerebellar hematoma evacuation. For patients with cerebellar hemorrhage undergoing surgical decompression, outcomes are more variable, with mortality ranging between 27% to 48% (91). Current AHA guidelines recommend evacuation of cerebellar hemorrhages greater than 3 cm for improved outcomes, though this is based on expert consensus (26). A systematic review and meta-analysis of observational studies evaluating the outcomes following surgical hematoma evacuation versus conservative management found the proportion of patients with favorable outcomes at 3 months was similar in both groups; however, survival was higher at 3 and 12 months in those who had the blood removed. The survival benefit seemed to be conferred by evacuation of larger volume hematomas (52).

Increasing interest in minimally invasive surgery techniques for intraparenchymal supratentorial hemorrhages has also led to an interest in similar techniques for infratentorial lesions. Minimally invasive surgery utilizes a small burr hole with or without neuronavigation or an endoscopic approach to remove blood instead of a traditional craniotomy. However, similar to suboccipital craniotomy literature, the use of this treatment modality for cerebellar hemorrhages has not been rigorously evaluated. It is hypothesized that a smaller craniotomy and durotomy can lead to shorter cases and lower complication rates.

Outcomes

Mechanical thrombectomy. The literature regarding outcomes following posterior circulation mechanical thrombectomy is limited, and there have been conflicting results of trials and meta-analyses.

A meta-analysis of posterior circulation clot removal found a favorable outcome (MRS 0 to 2) in nearly 40% and a mortality rate of 30% on 3-month follow-up (53). Distal basilar artery occlusion, good collateral circulation, shorter time to recanalization, and successful recanalization were associate with improved clinical outcomes on follow up (48; 24; 53; 87).

In another meta-analysis, mechanical thrombectomy of the posterior circulation was associated with worse functional outcomes than mechanical thrombectomy of the anterior circulation, though the former had a lower risk of symptomatic intracranial hemorrhage (92).

Both the BEST trial as well as the BASICS RCT failed to show an outcomes benefit of endovascular thrombectomy over medical management (IV tPA), with a non-significantly higher symptomatic intracerebral hemorrhage rate in the endovascular thrombectomy group (60; 54).

However, the ATTENTION trial (012 hours from symptom onset) and the BAOCHE trial (624 hours from symptom onset) presented at the 2022 European Stroke Conference showed improved outcomes as well as mortality benefit of endovascular thrombectomy for basilar artery occlusion (34; 63; 81).

All the above trials have shown a slightly greater risk of procedural complications and more symptomatic intracerebral hemorrhage after endovascular thrombectomy.

There are not enough data regarding outcomes for other regions of posterior circulation strokes, including posterior cerebral artery occlusions and vertebral artery occlusions; more studies are needed.

Suboccipital craniotomy. Several prospective randomized studies (DESTINY, HAMLET, DECIMAL) have compared the use of decompressive craniectomy for the treatment malignant middle cerebral artery versus medical management, demonstrating clear mortality benefit and functional outcome in pooled analysis (85). However, evidence for suboccipital craniotomy is based on observational studies. There is currently no high-quality evidence on this topic. Although a randomized study would be ideal, the high estimated rate of mortality (80%) in untreated patients makes this difficult to study prospectively. Patients who progress to requiring suboccipital craniotomy for decompression of cerebral edema or cerebellar hemorrhage do experience a survival benefit, but a high proportion continue to have significant morbidity. A meta-analysis of 11 papers (1 multicenter prospective, 10 retrospective) found a pooled event rate mortality of 19.9% and unfavorable outcomes (MRS 3 to 5 or GOS 2 to 3) in 28% (07). Complication rate from surgery was 22.9% and included cerebral spinal fluid leak, meningitis/ventriculitis, pneumonia, venous thromboembolism, and cardiac events (07). Age less than 60, surgery within 48 hours, higher preoperative Glasgow Coma scale, external ventricular drain insertion with the suboccipital craniotomy, less than one third volume of the cerebellum affected, and no brain stem involvement portended better outcomes (46; 07). Statistically significant predictors of poor outcome were bilateral cerebellar involvement and brainstem stroke (07).

Furthermore, there may be a difference in outcome with surgery for cerebellar ischemic infarctions versus hemorrhages. A retrospective review comparing outcomes in patients who underwent suboccipital craniectomy for hemorrhages and infarctions at a single institution found increased mortality, increased need for tracheostomy, and poorer outcomes at 6 months in patients with hemorrhages compared to ischemia (57). Though limited by its retrospective design and inability to match patients in the two groups, this highlights a possible difference in outcomes that may require further scrutiny in future clinical research.

In a case series of 10 patients from a single institution with intracerebellar hemorrhage greater than 3 cm, a 1 to 2 cm craniotomy was performed over the area where the hemorrhage was closest to the surface (41). On average, the operative time was less than an hour and patients had an average MRS of 2 on outpatient follow up. One patient had a tracheostomy and feeding tube placement, and one required an external ventricular drain. No patients had repeat bleeding, infection, or pseudomeningoceles.

A multicenter study of six patients used neuronavigation guided minimally invasive surgery for cerebellar hemorrhage evacuation with improvement in two of three and no clinical change in the other one of three (43). The median MRS was 3, though two patients passed away (one from withdrawal of care due to no clinical improvement and one from liver failure despite neurologic improvement).

In an observational comparison study of 41 patients (15 endoscopic guided vs. 22 traditional craniectomy), patients with minimally invasive surgery evacuation had nearly half the surgical time as conventional craniotomy, less bleeding time intraoperatively, similar postoperative complication rates, and the same outcome rates (06). Taken together, these studies present an exciting new possible avenue for therapy that will need to be further investigated with prospective studies.

Patients who progress to requiring suboccipital craniectomy for decompression of cerebral edema or cerebellar hemorrhage do experience a survival benefit, but a significant proportion continue to have morbidity. One meta-analysis demonstrated that with surgical decompression for cerebellar infarction, approximately half of patients had good outcomes defined as MRS 0 to 2. Even with surgical decompression, mortality in this study was 19.9%. The statistically significant predictors of poor outcome were bilateral cerebellar involvement and brainstem stroke. Complication rate from surgery was 22.9% and included cerebral spinal fluid leak, meningitis/ventriculitis, pneumonia, venous thromboembolism, and cardiac events (07).

For patients with cerebellar hemorrhage undergoing surgical decompression, outcomes are more variable, with mortality ranging between 27% to 48% (91). Increasing interest of minimally invasive techniques for intraparenchymal supratentorial hemorrhages has also led to interest in similar techniques for infratentorial lesions. The data are limited and unclear if improvement in outcomes or complication rates will be demonstrated (41).