Discussions:

Question

Babaji


Dear Mr Solanki,

Congratulations on the elegant work on posterior calvarial augmentation for hind brian herniation.

I think hind brain herniation is the final common pathway of different pathogenesis. It would be good to search for the underlying cause and construct surgical management depending on the cause. In your presentation you have nicely demonstrated that supratentorial crowding as one mechanism. Again, it is likely that many causes can lead to supratentorial crowding.

In your patients do you regularly perform pre-op i) CTV or MRV and ii) pre-op ICP measurements?

Thank you and look forward to hearing from you.

Yours sincerely,
Naren
G Narenthiran
Southampton, UK

Answer

Dear Naren,
Thank you for your insightful comments!

“I think hind brain herniation is the final common pathway of different pathogenesis.” => Agreed
I am fond of dividing the causes into 3 groups: Above the Foramen Magnum, at the Foramen Magnum and Skull base and below the Foramen Magnum

Above the FM:
This list includes conditions that “push the brain down from above” such as a thick skull from osteopetrosis, Familial Hypophosphataemic Rickets, Sickle Cell disease, craniosynostosis syndromes and generally any condition that leads to cranio-cephalic mismatch. Brain Tumours, vascular conditions(AVMs) and rare but true even hydrocephalus due to aqueductal stenosis. Small cranium, particularly posterior fossa.

At the FM:
Dolichoid Dens, a wide foramen magnum, Horizontal Clivus.
Children with a tight FM tend not to have a Chronic Hindbrain Hernia(CHH). One example of that is achondroplasia where despite macrocephaly and ventriculomegaly, those patients may not develop CHH.

Below the FM:
Conditions that create spinal CSF Hypovolaemia, and decrease the buoyancy of the brain, such as a lumbo-peritoneal shunts, causing gradual tonsillar collapse into the spinal canal.
“A pull from below” conditions where there is a tethered cord with a spina bifida and neural tub edefect (NTD). These will lead to Chiari type II, which essentially involves a rotated position of the posterior fossa and herniation of the medulla and cerebellum. The classic description of Chiari was for type I and Arnold one of Chiari’s colleagues noted the connection with neural tube defects, the type II also named as Arnold-Chiari Malformation type II.


“In your patients do you regularly perform pre-op i) CTV or MRV and ii) pre-op ICP measurements?”
Yes pretty much every patient would have undergone ICP measurement unless there was an overriding reason.
In addition they get an MRI/V as part of their pre-op workup, whole spine MRI to rule out syringomyelia, tethered cord,etc.

It is interesting to note that not all tonsillar hernias behave the same way. Many do not have acutely raised ICP (although some do) as they tend to “adjust” over a period of time.

Hope this helps

kind regards

Guirish
Guirish Solanki
Birmingham, UK

Question

Regression of chronic hindbrain hernia following posterior calvarial augmentation in children: New insights into pathology of hindbrain hernia
Guirish Solanki, Umar Farooq, Paul Davies (UK)

Dear Guirish,

Impressive presentation and excellent results with this new approach in treating Chiari Malformations.
Do you think that there is place for calvarial augmentation in young adults?
Would you consider the cervico-medullary kink as a characteristic of Chiari II malformation?

Many thanks,

Nik

Nikolaos G Tzerakis
Stoke-on-Trent, UK

Answer

Dear Nik,
Thank you very much for your very important questions!

“Do you think that there is place for calvarial augmentation in young adults?”
Yes, indeed this is a progressive disease. Some children will remain stable and their CHH will not progress.
Up to 73% remain stable, 19% will improve. 23% will get worse and about 14% will head for surgery.

The Adult Chiari Malformation (ACM) is noted at about 16 to 25 years of age. The diagnosis is made, on average, 5 years from onset of symptoms.
There is a strong association between the Chiari malformations and syringomyelia. About 30% of type I Chiari malformation and 45% to 90% of type II Chiari malformations
have an associated syrinx. The syrinx associated with the ACM usually is cervical or cervicothoracic.

If an Adult CM progresses and or develops a syrinx, I would consider surgery.
Evidence in children suggests that a Tonsillar Hernia of >12mm, age >100 months, with a ratio of the sagittal diameter of the foramen magnum to posterior fossa height of >0.6 and the ratio of the clival angle to FM to Clivus angle of < 0.8 are high risk factors for development of a syrinx.
More importantly the loss of CSF at the CCJ is an important factor in decision-making.

To determine subject suitability for Posterior calvarial augmentation I would recommend reviewing the MRI appearances of someone with supratentorial crowding.
The surgery itself is not difficult but there is a learning curve and issues like how much to expand, where to make the cuts, where to secure the plates need to be clear prior to surgery.


Would you consider the cervico-medullary kink as a characteristic of Chiari II malformation?

I think it can happen in the Chiari I as well particularly in advanced cases, when the skull base changes secondary to a small posterior fossa and crowding.
The hallmarks of the Type II include, a larger cerebellar vermian displacement, low lying torcular herophili, tectal beaking, and hydrocephalus with consequent clival hypoplasia
The cervico-medullary junction lies often within the spine and is usually kinked!

Hope this helps.

kind regards

Guirish
Guirish Solanki
Birmingham, UK

Question

Very interesing presentation by Dr Solanki
I have few questions.
What was primary indication for posterior calvarial augmentation?craniosynostosis?
Do you consider these patients as Chiari 1?
Are they symptomatic with Chiari?
Do you have have actual volume measurements supratentorial/infratentorial preop and post op?
Ventricular catheter is used for ICP monitoring?
Any procedural morbidity?

Thanks
Promod Pillai
Columbus OH

Answer

Dear Promod,
Thank you for your important questions.


What was primary indication for posterior calvarial augmentation? craniosynostosis?

The first indication we used it for was syndromic craniosynostosis with raised intracranial pressure, copper-beaten skull and papilloedema. All the children improved symptomatically but there were also very clear radiological improvements such as increased CSF flow and gradual regression of the chronic hindbrain hernia(CHH) / tonsillar hernia (TH) in those patients with it.
We followed these children up carefully with serial imaging and were able to confirm that the improvements continued serially over 5 years. It became clear to us that this procedure improved hindbrain hernia and csf flow at the foramen magnum without major and risky surgery at the CCJ.

From here I went on to develop clear radiological criteria for those cases were the procedure had proven successful and using this criteria we operated on this series of Chiari I patients with a very rewarding improvement in their tonsillar hernia as well as in the resolution of their syrinx.

Cases operated on outside of craniosynostosis, with Chiari I & Syringomyelia include Sinus Pericranii, children with Hypophosphataemic Rickets, Idiopathic Intracranial Hypertension, Sickle Cell Disease, Osteopetrosis and Simpson-Golabi syndrome amongst others.

Do you consider these patients as Chiari 1?

The contemporary definition of Chiari I is radiological and implies a simple cerebellar tonsillar descent more than 5 mm. From that point of view I consider them as Chiari I anomalies rather than Chiari II.

I myself prefer the terms Acute or Chronic Hindbrain Hernia, which factually represent an anatomic abnormality in a temporal fashion.

In syndromic craniosynostosis CHH is present in a number of syndromic conditions with the following frequency:
Pfeiffer’s syndrome 50%
Crouzon’s syndrome 70%
Oxycephaly 75%
Kleeblattschädel deformity 100%
Apert’s <5%
CHH is also associated with single suture synostosis particularly metopic and Lambdoid synostosis, but may be present in bicoronal, and sagittal synostosis as well.
(Truly whether we call it a Chiari I or Chronic Hindbrain Hernia, they represent the same anatomic abnormality, i.e a simple tonsillar hernia lower than 5 mm below the foramen magnum, without medullary, 4th ventricular or cerebellar herniation)

Are they symptomatic with Chiari?
The children we have operated have all shown progression of their craniosynostosis conditions or have shown an increase in their Chiari or have developed a new syrinx or a worsening in their syrinx.

Our criteria for surgery included clinical deterioration, radiological deterioration that is congruent with the clinical picture before we proceed to this surgical option. The indication for surgery in craniosynostosis was not Chiari but the cranio-cephalic disproportion causing raised intracranial pressure. In children without craniosynostosis, increasing headaches, incoordination, papilloedema, raised ICP, gait clumsiness and radiological deterioration of chiari and/or syrinx were considered for surgery.

Syringomyelia particularly is a silent disorder and often the clinical picture lags behind radiological changes. Equally isolation of Chiari specific symptoms in children with overwhelming problems related to syndromic craniosynostosis is quite difficult, including the presence of sleep apnoea, gait deterioration, visual deterioration and swallowing problems. Non-syndromic children on the other hand were symptomatic for Chiari and or had worsening of their syrinx and considered to be as a result of the Chiari I.

Do u have have actual volume measurements supratentorial/infratentorial preop and post op?

We performed volume measurements in another study of 224 MRI scans to define the posterior fossa and the foramen magnum in children with Chiari I, Chiari II and Craniosynostosis with Chronic Hindbrain hernia. Volumetric measurements related to Chiari with and without Syringomyelia has already been published from Birmingham in the past.
On this study we used Midline Surface Area measurements pre and post-operatively. We then combined these with angular and linear measurements of the supratentorial and infratentorial compartments and had our statistician tell us about the relevant parameters. We were equally surprised that a supratentorial procedure had increased the posterior fossa compartment but this was clinically and radiologically obvious once we review the images in light of this finding. We have reported these results in our presentation. Essentially the AP increase in the ST compartment led to a less steep tentorial angle and a decrease in the height of the posterior fossa at the apex of the tent, but overall an increase in the Surface area due to the rise of the tentorium.

It was also interesting to note that the Clival angle also changed suggesting that the skull base changes are secondary to the supratentorial crowding and reversible!!!

Ventricular catheter is used for ICP monitoring?

No, we use the Camino optical fibre parenchymal pressure monitor.

Any procedural morbidity?

In the 90’s Birmingham led the way in pioneering a new procedure in craniofacial surgery for syndromic craniosynostosis, termed “posterior calvarial release”. This was aimed at syndromic children with severe cranial compression and it was to provide an early brain decompression in a better way than the standard “workhorse” of craniofacial surgery the fronto-orbital advancement and remodelling” (FOAR). The procedure had its pros and cons. One problem was that children lying on their backs soon led to fusion of the release.
The procedure was used until about 2003 when we modified it by not just releasing the bone but actually augmenting the calvarium and holding the augmentation fixed by resorbable plates. There are several technical variations that we developed but essentially it increases the supratentorial and occipital compartment by about 1 to 2 inches posteriorly. This essentially prevented collapse but caused other problems such as wound dehiscence and resorbable plate and screw loosening amongst others. We have now modified this further to using metal plates and not expanding more than about 1 inch at a time and with satisfactory scalp closure.

A further innovation was started in 2006, when in some children we began performing a Dynamic Posterior Distraction Osteogenesis, that essentially uses linear single vector metal distractors and distracts a large “melon” slice of parieto-occipital released calvarium, 0.5 mm twice a day for 3 weeks. This has the effect of increasing the calvarial size but with lesser risks to wound dehiscence. Like previous procedures, there are associated complications. The procedure is associated with a greater risk of CSF leaks, screw loosening, wound infections and requires a second operation to remove the plates and screws.

We have had no mortality from this procedure, which we consider safer than the standard occipital craniectomy, C1 and C2 laminectomy with opening of the dura (with or without duraplasty) and resection of cerebellar tonsils.
This procedure does not involve opening of the dura or resection of parenchyma or laminectomy.

Hope this is useful and thank you for raising these very important surgical issues!


Finally a VERY HAPPY, HEALTHY AND PROSPEROUS 2012 TO EACH AND EVERYONE!

Kind regards

Guirish
Guirish Solanki
Birmingham, UK

(The e-mail address to contribute your questions and comments is: neurosurgeryresearch@jiscmail.ac.uk)

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