Central herniation [Neurosurgery Wiki]

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====== Central herniation ======

{{ ::central_herniation.png?400|}}

In the first phase of central [[herniation]], the [[diencephalon]] and the medial parts of both [[temporal lobe]]s 
are forced through a notch in the [[tentorium cerebelli]].

Caused by diffuse [[brain edema]] as seen in patients with [[severe traumatic brain injury]].

CT Scan shows effacement of the [[perimesencephalic cistern]]s and loss of [[Grey-white differentiation]].

===== Stages =====

==== Early diencephalic stage (reversible) ====

Early. May be due to diffuse bilateral hemisphere [[dysfunction]] (e.g. from decreased [[blood flow]] from increased [[ICP]]) or (more likely) from bilateral [[diencephalic]] dysfunction due to downward displacement. This stage warns of impending (irreversible) [[midbrain]] damage but is frequently reversible if the cause is treated.

=== Midbrain—upper pons stage ===

When [[midbrain]] signs fully developed (in adults), prognosis is very poor (extreme ischemia of midbrain). Fewer than 5% of cases will have a good recovery if treatment is successfully undertaken at this stage.
----

[[Consciousness]]: Altered [[alert]]ness is first sign; usually [[lethargy]], [[agitation]] in some. Later: [[stupor]] → [[coma]].

[[Respiration]]: Sighs, yawns, occasional pauses. Later: [[Cheyne-Stokes]].

[[Pupil]]s: Small (1–3 mm), small range of contraction.

[[Oculomotor]]: Conjugate or slightly divergent roving eyes; if conjugate then brainstem intact.

Usually positive [[DOLL’S EYE]]S and conjugate ipsilateral response to cold water calorics (CWC) in the [[caloric reflex test]]. Impaired upgaze due to compression of [[superior colliculus]] and diencephalic [[pretectum]]: [[Parinaud’s syndrome]] 

[[Motor]]: Early: appropriate response to noxious stimuli, bilateral Babinski, gegenhalten (paratonic resistance). If previously hemiparetic contralateral to lesion: may worsen. Later: motionlessness & grasp reflexes, then DECORTICATE (initially contralateral to lesion in most cases).

=== Lower pons—upper medullary stage ===
 

Respiration: Regular, shallow and rapid (20–40/min).

Respiration: Cheyne-Stokes → sustained tachypnea.

Pupils: Moderately dilated midposition (3–5mm), fixed. Note: in pontine hemorrhage pinpoint pupils appear because the loss of sympathetics leaves the parasympathetics unopposed, whereas in herniation, the parasympathetics are usually lost, too (3rd nerve injury).

Oculomotor: [[Doll’s eye]]s & CWC impaired, may be dysconjugate. MLF lesion → internuclear oph- thalmoplegia (when doll’s or CWC elicited and dysconjugate, medially moving eye moves less than laterally moving eye).

Motor: Decorticate → bilaterally DECEREBRATE (occasionally spontaneously).

Pupils: Midposition (3–5 mm), fixed.

Oculomotor: [[Doll’s eye]]s and CWC unelicitable.

Motor: Flaccid. Bilateral Babinski. Occasionally LE flexion to pain.


==== Late diencephalic stage ====


Patient becomes more difficult to arouse

Localizing motor responses to pain disappear and [[decorticate posture]] appears with eventual progression to 
decerebrate posturing

Progressive 
diencephalic 
impairment is thought to 
be the result of 
stretching of the small 
penetrating vessels of 
the posterior cerebral 
and communicating 
arteries which supply 
the hypothalamus and 
thalamus
----
As herniation progresses to the 
midbrain stage signs of oculomotor 
failure appear

The pupils become irregular and then fixed 
at midposition

Oculocephalic movements become more 
difficult to elicit

Extensor posturing appears spontaneously

Motor tone is increased and plantar 
responses are extensor
----
The progression of symptoms indicates 
irreversible ischemia and therefore 
intervention must occur before the 
midbrain stage to prevent permanent 
deficits from central herniation

==== Medullary stage (terminal stage) ====

Respiration: Slow, irregular rate and depth, sighs/gasps. Occasionally hyperpnea alternating with apnea

Pupils: Dilate widely with hypoxia.

===== Clinical characteristics differentiating uncal from central herniation =====

● decreased consciousness occurs early in [[central herniation]], late in [[uncal herniation]]

● uncal herniation syndrome rarely gives rise to decorticate posturing 

===== Outcome =====

In a series of 153 patients with signs of central herniation (altered level of consciousness, anisocoria or fixed pupils, abnormal motor findings) 9% had good recovery, 18% had functional outcome, 10% were severely disabled, and 60% died
((Andrews BT, Pitts LH. Functional Recovery After Traumatic Transtentorial Herniation. Neurosurgery. 1991; 29:227–231)).

Factors associated with a better result were young age (especially age≤17 yrs), anisocoria with deteriorating Glasgow Coma Score and nonflaccid motor function. Factors associated with poor outcome were bilaterally fixed pupils, with only 3.5% of these patients having a functional recovery.

===== Case reports =====

A 32-year-old female presented with a history of hydrocephalus and ventriculoperitoneal shunt placement at 9 months of age. She began experiencing significant headaches in college, later accompanied by stereotypical 5- to 25-minute episodes of unresponsiveness, posturing and pupillary dilatation, and failing anticonvulsant therapy. No neurosurgical evaluation was sought because of small ventricles on brain imaging. Episodes became progressively more frequent over a 10-year period, eventually occurring daily. On presentation, 5 clinical events were captured on EEG over 12 hours of monitoring. With each episode, she became unresponsive and hypertensive, with fixed, dilated pupils and flexor posturing. Between events, she was awake and alert, without confusion or postictal state. She had [[papilledema]] and limited extraocular movements, with normal [[pupil]]s and [[vital sign]]s. Computed tomography scanning showed small [[ventricle]]s. A shunt [[tap]] revealed no flow. With each episode onset, an EEG revealed an abrupt background rhythm slowing to 2-3 Hz delta range without epileptiform discharges. Between events, EEGs displayed normal waveform activity. Emergent ventriculoperitoneal shunt revision resulted in no further episodes in a 4-year follow-up period.

[[Slit Ventricle]] Syndrome can lead to severe intermittent [[brainstem]] [[herniation]] [[syndrome]] in the setting of shunt malfunction. [[Seizure]] [[diagnosis]] should be reserved for cases with proven functional shunt and [[EEG]] confirmation of [[epileptiform]] activity
((Hamilton K, Koueik J, Maganti R, Iskandar B. Slit Ventricle Syndrome Leads to 10-Year History of Repetitive Transient Central Herniation Masquerading as Seizures: Hydrocephalus Case Report. World Neurosurg. 2019 Jun;126:134-138. doi: 10.1016/j.wneu.2019.02.106. Epub 2019 Mar 1. PMID: 30831286.))
----
A 62-year-old man with gait disturbance due to subdural fluid collection (SDFC) who underwent burr hole irrigation and additional craniotomy, in which postoperative deterioration resulted from rapidly progressing central herniation with a large amount of air accumulation. Epidural blood patch with saline infusion in the thoracic spine finally resolved central herniation.

SDFC deteriorating after surgery has never been reported. SDFC has communication with CSF differing from mature CSDH composed of closed cavity surrounded by neomembrane. Under situations of CSF hypovolemia due to spinal dural tear, opening the cranium can prompt air replacement in the CSF space, which might represent a substantial risk for central herniation caused by a rapid loss of buoyancy force
((Haku T, Motoyama Y, Takamura Y, Yamada S, Nakagawa I, Park YS, Nakase H. Central Herniation Induced by Craniotomy Prompting Air Replacement for Subdural Fluid Collection Due to Cerebrospinal Fluid Hypovolemia. World Neurosurg. 2018 Sep;117:182-185. doi: 10.1016/j.wneu.2018.06.059. Epub 2018 Jun 18. PMID: 29929033.))