Shunt-induced craniocerebral disproportion (CCD)

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Parent item

Slit ventricle syndrome

General

• Aka
• Cephalocranial disproportion
• Not fully accurate because it means skull and head disproportion
• Cranioencephalic disproportion
• Craniocephalic disproportion
• Encephalo-cranial disproportion
• Post-shunt craniosynostosis
• Hyperostosis cranii
• Shunt-related sutural stenosis
• Secondary synostosis
• Secondary craniosynostosis
• Shunt-induced craniostenosis
• Shunt-induced suture ossification
• Secondary craniostenosis
• Secondary microcrania
• Iatrogenic small calvaria
• “A packaging problem”

Definition

• As a state where the volume of the brain exceeds the available intracranial space such that the skull cannot adequately accommodate the growing brain and/or normal physiological increases in the intracranial contents (blood flow and cerebrospinal fluid [CSF]), as suggested by
• Stereotypical radiographic signs
• The presence of plateau waves on intracranial pressure (ICP) monitoring

Numbers

• No clear incidence or prevalence as it is not a commonly study topic

• Using other factors we can predict prevalence of CCD
• 42 % of shunted adolescents have severe, disabling, headaches
• Slit ventricle syndrome.
• Chronic, debilitating headaches among shunted children within a unified pathophysiologic framework of conformational and functional changes in the ventricular system.
• Though radiographic slit-like ventricles are a frequent finding in shunted patients, the majority belong to relatively asymptomatic patients.
• Symptomatic slit ventricle syndrome occurs in 1–37 % of shunted children

Aetiology

Primary CCD

• Caused by any primary pathological process that leads to diffuse calvarial thickening or premature suture ossification and closure
• Pancraniosynostosis (nonsyndromic)
• Syndromic craniosynostosis
• Pyknodysostosis
• Craniodiaphyseal dysplasia, lionitis
• Camurati–Engelmann’s disease
• Cranial osteopetrosis
• Chronic anemia with diploic erythroid hyperplasia
• Hypophosphatasia Vitamin D-resistant rickets
• Hyperthyroidism
• Hyperparathyroidism
• Idiopathic

Secondary CCD

• An iatrogenic phenomenon specifically initiated by shunting in infancy or early childhood
• Shunted hydrocephalus before the age of 3 years

Clinical features

• Chronic, debilitating headaches in shunted patients
• Analgesics often fail to ameliorate these headaches,
• These headaches are often of a severity significant enough to interfere with daily activities, including schoolwork or occupational performance
• Headaches of CCD can be localized to areas where the crests of the cortical gyri approach the inner layer of the pain sensitive dura along the convexities.
• Headache comes on with raised ICP during ICP studies

• Other symptoms
• Irritability
• Ataxia
• Visual disturbances
• Dizziness Lethargy
• Developmental delay
• Decline in school performance
• Social withdrawal

Mechanism

• Normal Skull growth
• By early adulthood, the skull has essentially assumed Monro and Kellie’s rigid container, becoming relatively fixed and inelastic. It is then unable to accommodate significant increases in intracranial volume without potentially dire consequences

• Shunting (When opened have a low resistance to flow) → long term dampening of the cerebral pulse pressure (increase in CSF compliance) → a deficit of the expanding force → can lead to A) excessive thickening of the cranial vault B) Premature suture ossification/fibrosis → the result is an (often) “non-expansile, smaller than normal skull allowing no compensatory room for fluctuations in intracranial volume

• Shunting → drains ventricular CSF more than cortical subarachnoid CSF → Pressure gradient forms between Cortical subarachnoid space and ventricular space → Cortex push gets sucked away from the skull inwards → ventricle collapses → Ventricle has less ability to change size in response to elevation of ICP

• Lack of intracranial space in patients with CCD → crowding of the vascular structures within the cerebrum → congestion of intracerebral veins both within the cranium and at their outlet foramina → this impairs venous outflow →
• Increase venous pressure → increases ICP
• Hampers the brain’s ability to buffer changes in intracranial volume → causing pathological increases in ICP
• Brain remained tense and engorged with venous blood until the bone overlying the sagittal [sinus] and torcula were removed, following which it immediately became ‘lax’

Investigation

X-ray

• “Thumbprinting” appearance

• “Copper beaten” appearance

• Lamination of the diploe

CT/MRI

• Thickened vault

• Erosion of the inner table from the underlying gyri, thickening or lamination of the diploe, and overlapping, closure, or sclerosis of the sutures may also be seen

• Ventricles
• Normal
• Small slit like

• Foci of cartilage formation or ossification may be visible along the sutural margins

• Lack of CSF signal over the convexities, obliteration of cortical subarachnoid spaces

• Effacement of basal cisterns

ICP

• Pathophysiology of plateau waves in CCD
• A sign of
• Cerebrovenous congestion
• Increased cerebral elastance/decreased compliance
• Appearance of plateau waves on ICP monitor requires defining two physiologic concepts
• Elastance
• Elastance is “stiffness”—the brain's ability to resist deformation.
• A brain with increased elastance (i.e., greater stiffness) will manifest high pressures in response to increases in intracranial volume
• Compliance.
• The brain’s ability to change in volume—to stretch or recoil—in response to changes in ICP
• Inverse of elastance
• Increased compliance will be able to yield and “make room” more successfully in response to increased ICP.

• Plateau wave
• Altered compliance of the intracranial space are sufficient to explain most plateau wave phenomena
• The exact clinical significance of plateau waves is still up for debate
• During the plateau wave, there is a relative increase in relative cerebral blood volume (CBV) in the cerebral hemispheres and a relative decrease in relative CBF
• This relative increase in CBV is predictive for the headaches of CCD
• Attempt to correlate temporally the often paroxysmal nature of the severe headaches in these patients with the pathologic rises of ICP. Only after such a link is confirmed can the diagnosis of CCD be solidified

Diagnostic algorithm for CCD

• If a temporal correlation between the headaches and the presence of plateau waves on ICP monitoring, we diagnose the patient with CCD

• Working with the craniofacial surgery service, offer the patient a cranial expansion procedure in which rigid cranial vault distractors are affixed to the skull,
• ICP monitor is kept in place to continue to monitor the ICP and distract the skull daily until the presence of plateau waves has ceased

• Remove the ICP monitor and external distractors in the operating room and the patient is discharged home after a brief inpatient convalescence

Management

• LP shunts
• Idea is that since it drain subarachnoid CSF rather than ventricular CSF is can create space between cortex and dura → this can reduce stretching of the pain sensitive dura
• Its very sceptical if this produce a long term solution

Skull expansion

Skull-enlarging procedures

• Diminish the ICP by
• Increasing the cranial capacity
• Probably by permitting the expansion of the subarachnoid spaces along the cerebral convexities

• Providing more space for the brain parenchyma, the vasculature, and the CSF-containing cisterns and spaces

Technique

Cranial morcellation (cut into smaller pieces)

• Morcellation of the skull from the coronal suture to the transverse sinus posteriorly and to the squamosal sutures laterally

• Morcellation was meant to “vent” the pressure waves

Fronto-orbital advancement

• Frontoorbital advancements with remodeling of the anterior cranial vault were performed as a means ofproviding adequate intracranial volume

• Cosmetically better than Morcellation

Distraction osteogenesis

• Simultaneous utilization of ICP monitors and gradual cranial vault distraction via rigid external cranial vault distractors

• Distraction osteogenesis can be defined as the surgical induction of bone growth by applying a distractive force across an osteotomy site

• Pros
• Allows us to tailor treatment to the individual patient, whereby each patient can be distracted to the point in which he or she no longer demonstrates evidence of plateau waves on ICP monitoring
• Different patients will require different lengths of distraction in order to achieve cessation of plateau waves