Cerebral Larva Migrans

Cerebral larva migrans is a devastating neurological condition in rabbits caused by the migration of parasitic roundworm larvae through the brain and spinal cord tissue. This condition represents one of the most serious parasitic threats to domestic rabbits and is primarily caused by larvae of Baylisascaris procyonis, the common raccoon roundworm, though Baylisascaris columnaris from skunks can occasionally cause similar disease. The term cerebral larva migrans describes the clinical syndrome that results when these larvae, accidentally ingested by a rabbit, travel through the central nervous system causing progressive and typically irreversible neurological damage.

The condition develops when rabbits ingest embryonated eggs of Baylisascaris species that contaminate their food, bedding, or grazing areas. Raccoons, which are the definitive hosts for B. procyonis, shed enormous numbers of eggs in their feces, and these eggs can survive in the environment for years. When a rabbit consumes these eggs, larvae hatch in the intestine and begin an aggressive somatic migration, showing particular affinity for nervous tissue. Once in the brain, the larvae continue to grow and move, creating tracks of destruction through the neural tissue and triggering intense inflammatory responses that compound the damage.

The impact of cerebral larva migrans on rabbit health is catastrophic and almost uniformly fatal once clinical signs develop. The migrating larvae cause both mechanical damage through their movement and growth, and immunological damage through the inflammatory response their presence triggers. As larvae travel through the brain, they destroy neurons and create areas of malacia, or tissue softening, surrounded by zones of inflammation. The cerebellar region is often severely affected, leading to the pronounced balance and coordination problems characteristic of this condition. Unlike many other causes of neurological signs in rabbits, cerebral larva migrans typically causes rapid, relentless deterioration.

Treatment of cerebral larva migrans is rarely successful because by the time neurological signs appear, the larvae have already caused substantial irreversible brain damage. Prevention through strict environmental management to eliminate raccoon exposure is the only reliable way to protect rabbits from this devastating disease. Rabbit owners, particularly those in North America where raccoons are common, must take the threat seriously and implement rigorous prevention measures. Any rabbit showing neurological signs that has potential exposure to raccoon-contaminated environments should receive immediate veterinary evaluation, understanding that prognosis is grave and humane euthanasia may be the most compassionate option.

The primary cause of cerebral larva migrans in rabbits is ingestion of embryonated eggs of Baylisascaris procyonis, the raccoon roundworm. Raccoons serve as the definitive host for this parasite, meaning adult worms live and reproduce in the raccoon intestinal tract. An infected raccoon can shed over 150,000 eggs daily in its feces, and these eggs require two to four weeks of environmental development before becoming infective. Once embryonated, the eggs are remarkably resistant to environmental conditions and can remain viable for years in soil, even surviving freezing temperatures. This persistence creates long-term contamination of areas previously visited by infected raccoons.

Baylisascaris columnaris, the common roundworm of skunks, can also cause cerebral larva migrans in rabbits, though this is less commonly reported than B. procyonis infection. The life cycle and pathogenesis are similar, with larval migration through tissues causing damage to whatever organs the larvae encounter. In areas where skunks are common, exposure to their feces poses similar risks to raccoon exposure. Both parasites create the same clinical syndrome of progressive neurological deterioration in infected rabbits.

Environmental contamination is the critical factor enabling infection. Raccoons are creatures of habit and establish communal latrine sites where they repeatedly defecate, creating areas of heavy egg concentration. These latrines may be located at the base of trees, on logs, on rooftops, in attics, barns, or any sheltered area the raccoons frequent. Hay or bedding harvested from or stored in areas accessible to raccoons may become contaminated with eggs. Grass, vegetables, or outdoor grazing areas can similarly be contaminated. The eggs are microscopic and invisible without magnification, so contaminated materials appear completely normal. This invisible contamination makes prevention challenging and the threat particularly insidious.

Risk factors for cerebral larva migrans relate entirely to environmental exposure rather than any inherent rabbit characteristics. Outdoor housing dramatically increases risk compared to indoor housing. Geographic location matters, with risk highest in areas with large raccoon populations, which includes most of North America. Housing rabbits in barns, sheds, or hutches accessible to raccoons creates high risk. Using hay or bedding from unknown sources or areas potentially accessible to raccoons increases exposure probability. Allowing rabbits to graze in gardens, yards, or pastures that raccoons may visit creates exposure opportunities. Young rabbits may face slightly elevated risk due to exploratory behaviors, but rabbits of any age can become infected.

The mechanism of cerebral larva migrans development begins when infective eggs are ingested. The eggs hatch in the small intestine, releasing larvae that penetrate the intestinal wall and enter the bloodstream. These larvae are aggressive migrators with a strong predilection for the central nervous system. Once in the brain or spinal cord, larvae continue to grow, reaching sizes of 60 to 75 micrometers in diameter. As they travel through neural tissue, they create physical tracks of destruction. Additionally, the larvae produce excretory-secretory antigens that trigger intense inflammatory responses, leading to granuloma formation, tissue necrosis, and glial scarring. The combination of direct mechanical damage and immunological injury creates the severe clinical syndrome. The cerebellum and brainstem are frequently severely affected, explaining the prominent vestibular and coordination deficits typically observed.

Early warning signs of cerebral larva migrans may be subtle and easily attributed to other causes, which is particularly tragic given the rapid progression of this disease. Initial symptoms might include mild changes in behavior, subtle coordination problems, or slight alterations in the rabbit's normal activity patterns. Because rabbits instinctively hide illness as prey animals, these early signs are often overlooked until the disease has progressed to obvious neurological dysfunction. Owners may notice their rabbit seems slightly off or less coordinated than usual without recognizing the significance. Any change in a rabbit with potential raccoon exposure should prompt immediate veterinary evaluation.

The most commonly observed symptoms of cerebral larva migrans involve progressive neurological deterioration affecting balance, coordination, and movement. Head tilt, medically termed torticollis, causes the rabbit's head to rotate persistently to one side and is among the hallmark signs. Ataxia, or loss of coordinated movement, becomes increasingly apparent as the rabbit struggles to walk normally and maintain balance. Circling behavior develops as the rabbit walks repeatedly in circles, typically in the direction of the head tilt. Tremors, particularly affecting the head, may be prominent. Rolling episodes may occur, with affected rabbits unable to right themselves. These symptoms typically worsen progressively over days to weeks as larvae continue migrating through brain tissue.

Behavioral changes associated with cerebral larva migrans are profound and distressing to witness. Affected rabbits become disoriented and confused, often appearing unaware of their surroundings. Lethargy progresses rapidly, with rabbits becoming increasingly unresponsive. Appetite typically decreases dramatically, with many rabbits stopping eating entirely, which leads to the dangerous secondary complication of GI stasis within 12 to 24 hours. The hunched posture characteristic of pain or illness in rabbits is often observed. Teeth grinding, a well-recognized sign of pain and distress in rabbits, may be heard. Changes in response to stimuli, decreased social interaction, and apparent failure to recognize familiar people or environments all indicate advancing brain involvement.

Physical signs of cerebral larva migrans extend beyond purely neurological manifestations. Weight loss occurs rapidly as the rabbit stops eating. Muscle wasting may become apparent, particularly in the hindquarters. The coat condition often deteriorates due to inability to groom normally. Paralysis or weakness affecting the hindlimbs may develop as spinal cord involvement progresses. The rabbit may assume abnormal postures or be completely unable to right itself when placed on its side. In rare cases, larvae may migrate to the eyes as well as the brain, causing ocular abnormalities, though central nervous system involvement dominates the clinical picture in rabbits.

Symptom progression in cerebral larva migrans is typically rapid and relentless once clinical signs appear. Initial mild symptoms can progress to severe disability within days to a few weeks. The specific timeline depends on the number of larvae ingested and which areas of the brain are affected. Some rabbits may appear to stabilize briefly before experiencing further decline as larvae migrate to new areas or inflammatory responses intensify. The progressive nature of this condition means symptoms essentially never improve without intervention, and even aggressive treatment rarely changes the trajectory.

Emergency symptoms requiring immediate veterinary attention include seizures, which may manifest as sudden collapse, paddling leg movements, loss of consciousness, or rigid posturing. Opisthotonos, characterized by severe backward arching of the head and neck, indicates critical brainstem involvement. Complete inability to stand or maintain normal posture, rapid deterioration occurring over hours rather than days, and cessation of eating for more than 12 hours all constitute emergencies. Any difficulty breathing requires immediate attention. Given the extremely poor prognosis of symptomatic cerebral larva migrans, humane euthanasia is often the most compassionate choice, and this difficult conversation should be had promptly with a rabbit-savvy veterinarian.

The initial examination for suspected cerebral larva migrans begins with thorough history taking focused on environmental exposure risks. The veterinarian will ask detailed questions about housing arrangements, whether the rabbit lives indoors or outdoors, potential exposure to raccoons or areas where raccoons might have been present, and sources of hay and bedding. Geographic location is relevant, as raccoon populations and thus Baylisascaris prevalence vary by region. The physical examination includes complete neurological assessment evaluating mental status, balance, coordination, cranial nerve function, and reflexes. Finding a rabbit-savvy veterinarian familiar with exotic animal neurology is essential for accurate evaluation.

Diagnostic testing for cerebral larva migrans in living rabbits presents substantial challenges, and definitive diagnosis is typically only possible through postmortem examination. Blood tests including complete blood count may show eosinophilia, an elevation of eosinophils that can indicate parasitic infection, though this finding is neither sensitive nor specific for Baylisascaris. Serum chemistry panels assess overall organ function and help rule out metabolic causes of neurological signs. Serological tests to detect antibodies against Baylisascaris exist for research purposes but are not widely available in clinical practice. Advanced imaging such as MRI might reveal inflammatory changes in the brain consistent with parasitic migration, but these findings are not pathognomonic and cannot definitively distinguish cerebral larva migrans from other causes of encephalitis.

Differential diagnosis is crucial because several other conditions cause similar neurological signs and some are treatable. Encephalitozoon cuniculi is far more common than cerebral larva migrans and causes head tilt, ataxia, and other neurological signs that overlap substantially. E. cuniculi can be tested for serologically and often responds to fenbendazole treatment, making accurate differentiation clinically important. Pasteurella infections can cause vestibular signs through middle and inner ear involvement. Brain abscesses may present with progressive neurological deterioration. Toxoplasmosis, herpesvirus encephalitis, trauma, stroke, and neoplasia must all be considered. Clinical history, particularly evidence of raccoon exposure versus its absence, helps guide the diagnostic assessment.

Diagnosis confirmation of cerebral larva migrans unfortunately requires histopathological examination of brain tissue, which is only possible after death. At necropsy, the brain may show grossly visible malacic lesions appearing as soft, discolored tissue areas. The cerebellum, including the cerebellar peduncles, is often most severely affected. Microscopic examination reveals characteristic findings including large areas of malacia with activated astrocytic proliferation, focal necrosis with perivascular cuffing by lymphocytes and heterophils, and the diagnostic finding of larval cross-sections within brain tissue. The larvae show characteristic morphological features including cuticular alae that help identify them to genus. Because diagnosis in living rabbits remains presumptive, treatment decisions must be made on clinical suspicion while understanding that if cerebral larva migrans is truly the cause, prognosis is grave regardless of intervention.

Emergency and immediate treatment for rabbits with suspected cerebral larva migrans focuses on stabilization and comfort while acknowledging the extremely poor prognosis of this condition. If seizures are occurring, anticonvulsant medications such as diazepam or midazolam are administered to control seizure activity and prevent injury. Fluid therapy maintains hydration and supports overall physiological function. Pain management is essential, with meloxicam commonly used as a safe anti-inflammatory and analgesic in rabbits. If the rabbit has stopped eating, which occurs rapidly with neurological disease, syringe feeding with critical care formula must begin immediately to prevent GI stasis from compounding the neurological emergency.

Medical management attempts for cerebral larva migrans have historically shown poor results because significant irreversible brain damage has already occurred by the time clinical signs appear. Antiparasitic medications from the benzimidazole class, including fenbendazole, albendazole, and mebendazole, have activity against Baylisascaris larvae in experimental settings. However, these drugs cannot repair damage already done to brain tissue, and their ability to halt progression in clinical cases appears extremely limited. Fenbendazole at 20 mg/kg daily is often tried due to its safety profile in rabbits, though efficacy against established cerebral infection is uncertain. Albendazole may have greater larvicidal activity but carries more risk of bone marrow suppression and requires careful monitoring. Corticosteroids have been used in some protocols to reduce inflammatory responses, though their use remains controversial.

Surgical intervention has no role in treating cerebral larva migrans, as the parasitic larvae are distributed throughout the central nervous system rather than forming discrete masses that could be surgically addressed. The condition affects the brain parenchyma diffusely, making surgical approaches impossible. All treatment is therefore medical and supportive rather than surgical.

Supportive care forms the foundation of management for affected rabbits and includes elements critical for any seriously ill rabbit. Nutritional support through syringe feeding is absolutely essential, as most affected rabbits stop eating and GI stasis will rapidly worsen condition if the gut becomes static. High-fiber critical care formulas designed for herbivores should be administered every few hours. Hydration through subcutaneous fluids helps maintain kidney function and overall physiological status. The rabbit should be housed in a safe, padded environment to prevent injury during rolling, falling, or seizure episodes. Temperature support may be needed as debilitated rabbits often cannot thermoregulate effectively. Gentle handling and a quiet environment minimize additional stress.

Alternative or complementary treatments have no proven efficacy for cerebral larva migrans. Given the serious, rapidly progressive nature of this disease, pursuing unproven treatments should not delay appropriate medical care or timely discussions about humane euthanasia. Owner time and resources are better directed toward comfort care if treatment is attempted, or toward making the compassionate decision to prevent further suffering.

Treatment decisions for cerebral larva migrans are among the most difficult in rabbit medicine. The overwhelming probability is that affected rabbits will not survive regardless of treatment intensity, and those rare survivors may have severe permanent neurological deficits. Intensive care costs are substantial and outcomes remain poor despite best efforts. Honest, compassionate conversations with the veterinarian about realistic expectations are essential. Humane euthanasia is often the kindest choice for rabbits with severe or rapidly progressive neurological signs, sparing them from suffering during an inevitable decline. Quality of life should be the primary consideration, and rabbit owners should feel supported in making the most compassionate decision for their pet.

The recovery timeline for cerebral larva migrans must be understood in the context that recovery is extremely rare and should not be expected. In the unusual instances where a rabbit survives, which typically only occurs with very mild infections caught at the earliest possible stage, recovery is measured in months and is virtually never complete. Any neurological deficits present at diagnosis typically persist permanently because migrating larvae cause structural brain damage that cannot regenerate. Surviving rabbits require indefinite management of residual disabilities which may include permanent head tilt, chronic ataxia, and behavioral changes.

Post-treatment care for the rare surviving rabbit centers on supportive management and accommodation of residual deficits. Antiparasitic medication may be continued for extended periods, sometimes weeks beyond symptom stabilization, in hopes of eliminating any remaining larvae. The rabbit must eat adequate amounts of hay and vegetables to maintain GI function, with appetite monitored closely and supplemental feeding provided as needed. Follow-up veterinary appointments allow assessment of neurological status and adjustment of supportive care. Fecal output monitoring ensures healthy gut function continues. The living environment must be adapted to accommodate balance problems and prevent injury.

Prognosis factors for cerebral larva migrans are overwhelmingly unfavorable. The number of larvae ingested significantly affects disease severity, with heavier burdens causing more rapid deterioration. The specific brain regions affected determine which functions are impaired. Perhaps most critically, the time between infection and treatment initiation determines whether any meaningful intervention is possible, but the delay between infection and symptom onset means substantial damage has already occurred before owners or veterinarians are even aware a problem exists. Even with immediate aggressive treatment upon symptom recognition, most rabbits either die or require euthanasia due to progressive deterioration or unacceptably poor quality of life.

The long-term outlook for rabbits with cerebral larva migrans is realistically one of loss rather than survival in most cases. For the very rare survivors, lifelong accommodation of neurological deficits is necessary. Environmental modifications ensure safety despite balance impairments. The damage caused by migrating larvae is permanent, so symptoms present at the point of stabilization typically persist indefinitely. Recurrence of the same infection cannot occur once larvae have stopped migrating, but the damage they caused remains. Prevention of future infections through environmental management is essential if the rabbit is to be housed where exposure might reoccur. For most affected rabbits, the long-term outlook involves compassionate euthanasia rather than chronic management.

Primary prevention of cerebral larva migrans is absolutely essential because treatment of established infection is so rarely successful. Prevention centers on eliminating any possible exposure to raccoon or skunk feces, which contain the infective eggs of Baylisascaris species. Rabbit owners must take this threat seriously, understanding that once clinical signs develop, the prognosis is grave regardless of treatment efforts. Prevention requires knowledge of raccoon and skunk behavior, recognition of potential contamination sources, and implementation of rigorous environmental management to keep rabbits safe from these devastating parasites.

Environmental prevention focuses on physical separation between rabbits and any areas raccoons or skunks might access. Indoor housing provides the highest protection level, as these wild animals rarely enter occupied human dwellings. If outdoor housing is used, enclosures must be constructed to completely prevent access by raccoons and skunks, including solid floors that prevent digging, secure walls and roofing that eliminate entry points, and locks on doors since raccoons can manipulate simple latches. Areas around rabbit housing should be kept clean and free of food sources attracting wildlife. Gardens, compost bins, trash containers, and pet food dishes draw raccoons and should be secured or located well away from rabbit housing areas.

Dietary prevention emphasizes ensuring all food and bedding is free from wildlife contamination. Hay should be purchased from reputable sources that store products in wildlife-proof facilities. Hay harvested from fields accessible to raccoons or skunks, or stored in barns these animals can enter, poses unacceptable risk. The critical importance of unlimited grass hay in rabbit nutrition cannot compromise safety, so sourcing must be carefully managed. Fresh vegetables should be thoroughly washed. Produce from gardens potentially visited by wildlife should be avoided for rabbit consumption. Clean fresh water in protected containers prevents contamination.

Health maintenance supporting overall rabbit health helps ensure early detection of any problems. Regular veterinary visits with a rabbit-savvy veterinarian provide opportunities to discuss environmental risks and prevention strategies. While no vaccine exists against Baylisascaris, maintaining overall health through proper nutrition, appropriate housing, and stress reduction supports immune function. Regular weight monitoring and daily health observation help detect subtle changes that might indicate illness. Understanding normal rabbit behavior allows recognition of early abnormalities that warrant veterinary consultation.

Early intervention in potential exposure situations offers limited hope but should be considered. If a rabbit is known to have ingested material potentially contaminated with raccoon or skunk feces, immediate veterinary consultation is warranted. Some veterinarians may recommend prophylactic antiparasitic treatment, though effectiveness of this approach is uncertain. Because Baylisascaris eggs require environmental development before becoming infective, fresh feces pose less immediate danger than older deposits, but all wildlife feces should be considered hazardous. Daily health monitoring allows owners to recognize their rabbit's normal behavior and identify subtle early changes. Any neurological abnormality in a rabbit with potential wildlife exposure warrants immediate veterinary evaluation.

Daily management of a rabbit at risk for cerebral larva migrans requires vigilant environmental safety and health monitoring. Living spaces must be completely secured against wildlife access, with regular inspections identifying and repairing potential entry points. Food storage must prevent contamination. The rabbit's behavior, appetite, activity level, and coordination should be observed multiple times daily, with any changes documented and reported to the veterinarian promptly. For the rare rabbits recovering from infection, medication schedules must be followed precisely and syringe feeding techniques mastered in case appetite decreases.

The home environment requires careful configuration to maximize safety for at-risk rabbits. Indoor housing is strongly recommended in areas where raccoons and skunks are present. Any outdoor or outbuilding housing must completely exclude wildlife through solid construction, secure closures, and regular maintenance. Living areas should be located away from known wildlife activity areas. For rabbits with neurological deficits from survived infection, the environment must minimize fall hazards, provide secure footing to accommodate balance difficulties, and include protective padding. Temperature should remain in the comfortable range for rabbits, between 60 and 70 degrees Fahrenheit.

Quality of life considerations are paramount when managing rabbits affected by cerebral larva migrans. Rabbits with permanent neurological deficits can potentially maintain acceptable quality of life with appropriate accommodations, though severe deficits may preclude this. Signs of acceptable quality include interest in food and eating adequately, engagement with the environment, normal grooming attempts, comfortable resting, and absence of obvious pain or distress. Mental stimulation through safe enrichment, social interaction with human caregivers, and gentle attention supports wellbeing. However, inability to eat, severe persistent disorientation, continuous falling or rolling, and obvious distress indicate unacceptable quality of life requiring reassessment of continued care.

Monitoring and ongoing care includes regular health assessment and scheduled veterinary follow-up. Owners should recognize normal versus abnormal neurological status and report any changes immediately. Weekly weight checks detect subtle changes indicating developing problems. Daily tracking of food and water intake alongside fecal output ensures physiological function remains normal. For recovering rabbits, the veterinarian will establish a follow-up schedule assessing progress and adjusting care plans.

Caregiver support addresses the significant stress of managing serious neurological disease in a rabbit or living with environmental risk knowledge. The House Rabbit Society and similar organizations provide educational resources and community support. Local rabbit rescues may offer practical guidance. The financial costs of exotic veterinary care, particularly intensive neurological cases, can be substantial. Online communities connect rabbit owners facing similar challenges. When outcomes are not what was hoped, grief support resources help process loss. Owners should feel supported in making compassionate decisions for their rabbits' welfare.

Cerebral larva migrans does not show any breed predilection, meaning all rabbit breeds are equally susceptible if exposed to infective Baylisascaris eggs. The risk is determined entirely by environmental exposure rather than genetic factors. A purebred show rabbit housed indoors with carefully sourced hay faces minimal risk, while a mixed breed rabbit kept outdoors in wildlife-endemic areas faces significant danger regardless of breeding. This equal susceptibility spans all size categories from dwarf breeds to giant breeds and all coat types.

Certain management situations that may loosely correlate with rabbit types can affect exposure risk without representing true breed predisposition. Rabbits kept in commercial meat production are often housed in outdoor hutches potentially accessible to wildlife. Rabbits in educational or 4-H programs may be housed in barns or fair facilities where wildlife access is possible. Pet rabbits of any breed allowed outdoor grazing face elevated risk. Show rabbits transported to various locations may encounter contaminated environments. None of these represent breed-specific vulnerabilities, but management practices associated with different rabbit uses may inadvertently increase exposure.

Screening recommendations cannot rely on breed-based protocols since all breeds are equally susceptible. Instead, screening emphasizes environmental risk assessment. Rabbits with any potential wildlife exposure should be monitored especially closely for neurological signs. Unfortunately, no practical screening test can detect Baylisascaris infection before symptoms develop. Veterinarians in areas with raccoon populations should include cerebral larva migrans in differential diagnosis for neurological rabbits. Breeders, rescues, and individual owners should all implement strict environmental controls. When acquiring new rabbits, inquiring about previous housing conditions and potential wildlife exposure helps assess risk, understanding that infection may not become apparent for weeks after exposure.

Several conditions commonly co-occur with or complicate cerebral larva migrans. GI stasis develops rapidly when affected rabbits stop eating due to neurological impairment, and represents the most immediate secondary complication requiring aggressive management through syringe feeding and gut motility support. Hepatic lipidosis can develop from prolonged anorexia. Aspiration pneumonia may occur if swallowing becomes impaired or syringe feeding is performed improperly. Dehydration worsens rapidly without adequate fluid intake or supplementation. Secondary bacterial infections may develop in debilitated patients. These complications compound the already grave prognosis and must be addressed alongside attempts to treat the primary condition.

Conditions with symptoms similar to cerebral larva migrans must be differentiated to ensure appropriate treatment, as some are manageable while cerebral larva migrans generally is not. Encephalitozoon cuniculi is the most common cause of neurological signs in pet rabbits and produces similar symptoms including head tilt, ataxia, rolling, and circling. E. cuniculi can be tested serologically and often responds to fenbendazole treatment, making differentiation clinically critical. Pasteurella multocida causing inner ear infection results in vestibular signs resembling early cerebral larva migrans. Brain abscesses cause focal neurological deficits that may mimic parasitic migration. Herpesvirus encephalitis, though rare, produces severe neurological disease. Toxoplasmosis, trauma, cerebrovascular events, and brain neoplasia also enter the differential diagnosis.

Potential complications of cerebral larva migrans extend beyond neurological damage. Seizures may cause secondary injuries including muscle damage and hyperthermia. Recumbent rabbits develop pressure sores and urine scalding without diligent nursing care. Immunosuppression from physiological stress may allow secondary infections. In rare cases where larvae migrate to the eyes, permanent vision loss occurs. The systemic stress of severe neurological disease may precipitate cardiac events. Prevention of complications requires intensive supportive care, though the primary condition typically progresses regardless of how well secondary problems are managed. The most important related consideration is that GI stasis will develop within hours if the rabbit stops eating, making nutritional support absolutely essential regardless of neurological prognosis.