04/8/13

The Chiari Malformations, 6/6

Chiari, Part 6 of 6: The Tethered Cord

Chiari1Tethered Cord is a nearly universal finding after myelomeningocele (MMC) repair. It is the result of normal scarring after surgery, which can bind the spinal cord at the level of the MMC repair and prevent the cord from sliding the way it needs to with normal everyday movement.

It turns out that the tip of spinal cord is at about the level of the L3/4 disk in a newborn. However, because the spinal canal grows (lengthens) rapidly and the spinal cord does not, the normal spinal cord appears to ascend in the canal as the spine lengthens. By the first year, the cord has attained its normal position, with the tip at the level of the L1/2 disk space.

In a MMC patient, the post-op scarring from the initial repair surgery causes the spinal cord to form adhesions to the surrounding tissue, thus tethering it and preventing it from ascending. The spinal cord tolerates such stretching poorly, and the result is generally a reversal or loss of milestones. Patients become incontinent when they had previously been continent, gait changes and deteriorates, child may demonstrate shortening of their heel cords and appear to be walking on tip toes, back pain, headaches (especially when trying to flex neck to look down). In advanced cases, young kids will arch their backs and extend their necks (as if looking up all the time) and refuse to do otherwise. They become fussy and irritable.

Tethered cord tends to make its appearance during growth spurts, such as around puberty. Also commonly seen at four or five years of age.

Surgery involves general anesthetic and re-exploration of the previous repair site. Usually takes about 2 hours. Unfortunately, there is a risk of recurrent tethering. Most kids only need a single detethering, a few will need two surgeries (generally separated by many years). Occasionally an adult will present with a tethered cord.

Results are generally good, though it is better to prevent loss of function than to try to recover it once lost. For this reason, detethering is often undertaken at the first sign of trouble.

The greatest risk of surgery is that of making a patient worse. This is unusual, but not rare. It is more frequent during a revision.

Note that Chiari I is not associated with tethered cord. Also note that if a patient has a vp shunt, its proper function should be verified before operating on the tethered cord. If hydrocephalus is present or the vp shunt is not working, these things should be attended to prior to operating on the tethered cord.

Tethered cord surgery is generally elective and can be scheduled during school vacations.

 

End of Chiari Postings

 

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04/5/13

The Chiari Malformations, 5/6

Chiari, Part 5 of 6: Syringomyelia

Chiari1Syringomyelia is an enlargement of the central spinal canal, sometimes to hugh dimensions. This central canal is almost imperceptible on a normal MRI. A very small syrinx is of no consequence generally. However, when very large or showing enlargement over time on several MRIs, chronic spinal cord injury is occurring and loss of function (weakness, decreased feeling, decreased dexterity, even paralysis) can result.

Syringomyelia, when associated with Chiari, generally resolves or stabilizes with adequate treatment of the Chiari. Very rarely it will not, and then another source for the syringomyelia must be sought, such as a tethered cord or the very rare tumor of the spine.

There are many causes of syringomyelia. In Chiari I, the Chiari is generally assumed to be the culprit. In Chiari II, the problem can be the Chiari itself, hydrocephalus, a tethered cord, or some combination of all of these.

In Chiari I, the syrinx, if present, is generally in the mid-cervical range C4-C6, and this should be checked for on a pre-op MRI. In Chiari II, the syrinx can involve the entire spinal cord and imaging of the entire spine is necessary. This will generally show a radiographic tethered cord, which may or may not be clinically significant. In either Chiari I or II, the syrinx can extend into the brainstem itself, called syringobulbia. This is usually associated with lower cranial nerve problems (swallowing issues, facial pain, etc). Syringobulbia is rare and indicates a very advanced condition.

Unless tumor is present, it is rare to operate on a syrinx directly. Such surgery is generally disappointing and can be dangerous.

Here is a picture of a large focal syrinx behind (dorsal to) the C6-T1 vertebral bodies. The cause of this particular syrinx is not immediately apparent from this image, as there is no significant chiari. A syrinx this size almost certainly warrants treatment of some sort. I will discuss syrinx further in future post, as it is an important subject in itself, with many discussion points.

SyrinxFocal

Next time: The Tethered Cord

04/3/13

The Chiari Malformations 4/6

Chiari, Part 4 of 6: Chiari Decompression Surgery Chiari1The exact extent of surgical decompression in Chiari I and II is variable and based upon the degree of tonsillar decent into the upper cervical spinal canal. However, in both instances subocciptial decompression and upper cervical laminectomy are necessary. Duraplasty is often performed as well. What are these things exactly? In general, the problem is viewed as crowding at level of the foramen magnum and upper cervical canal. The idea, thus, is to make additional room and relieve the crowding. Think of the spinal canal as a ring of bone, sort of like a napkin ring actually. The idea behind Chiari decompression is to take a bite out of the back side of the ring, so as to turn a closed ‘O’ into an open ‘C’.  The back of the bony foramen magnum is removed, enlarging it by a centimeter or more in size. Laminectomy is the medical term for removal of the back of the vertebra, so as to open the ring. This is always necessary at C1, the first cervical vertebra below the skull, and often necessary at C2. That will usually be sufficiently for Chiari I decompression, but with Chiari II the decompression may rarely need to be carried all the way down to C5. Laminectomy at C1 & C2 is well tolerated, but in very young patients and in patients requiring more extensive laminectomies (C3-C5), future instability (excessive movement of the neck) may require screws, pins, and rods for stabilization. This is very difficult in children under 5 years and is one factor to consider in the timing of surgery. In additional to laminectomy, most neurosurgeons also do a duraplasty (but not all—ask). A duraplasty involves opening the dura, the tough layer that acts as a barrier between the brain & spinal cord and the rest of the body. The dura also effectively holds back CSF, so one consequence of opening it is the risk of a spinal fluid leak after surgery—this is virtually assured if hydrocephalus is present and is the reason for treating hydrocephalus prior to attempting a Chiari decompression. A post-op CSF leak puts the patient at risk of meningitis and may require re-operation to stop. Opening the dura, while increasing the risk of surgery slightly, is valuable in that it affords the opportunity to sew in a patch, a so-called expansion duraplasty. This has the effect of increasing the available space at the level of the decompression, effectively relieving the chronic compression on the brainstem and upper cervical cord. In the past, the cerebellar tonsils were removed as a part of this surgery. While a few neurosurgeons still do this, the majority do not. Removal of the tonsils generally does not cause a neurologic deficit, but it is now felt to be an unnecessary part of the operation. This surgery is done under general anesthesia (patient is entire unconscious) and generally takes about two hours, give or take. A redo operation (unusual but not rare) may take longer. Chiari I patients generally spend one night in the ICU and are out of the hospital in 2-3 days. Chiari II patients may be in hospital slightly longer, especially if there are other medical issues, as there tend to be in myelomeningocele patients. The most frequent complication of the surgery is pseudomeningocele, a contained CSF leak (one that does not come through the skin). It looks like a bag of water ballooning the skin, is unsightly, and may cause headache. If it doesn’t resolve on its own within a week or two, re-operation may be needed. Other complications include external CSF leak, infection (meningitis, wound infection), stroke, bleeding, delayed instability requiring future surgery, persistent headaches, and complications of the general anesthetic (minimal in Chiari I, patient dependent in Chiari II—patients are sicker, often with other medical issues). In Chiari I, surgery generally leads to resolution of the symptoms, though headache may persist and operating for headache alone is generally discouraged. In Chiari II, the symptoms are generally arrested or halted at their present level, though lost function may not return. Chiari decompression is generally (though not always) elective and can be scheduled during school vacations. Next time: Syringomyelia   fiction by Edison McDaniels… The trade paperback edition of the most amazing Civil War novel since Cold Mountain & The Killer Angels is now available! 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03/30/13

The Chiari Malformations 3/6

 

Chiari, Part 3 of 6: The Chiari II Malformation

Chiari1Chiari II malformation is virtually always associated with myelomeningocele, MMC. MMC patients are likely to suffer from three separate but related neurosurgical maladies: hydrocephalus (requiring treatment with a ventriculoperitoneal shunt), Chiari II malformation (often requiring decompression surgery), and the myelomeningocele itself (which is surgically repaired at birth but may later present as a tethered cord).

 Patients with Chiari II may have cognitive deficits and be developmentally delayed, though they need not be and the incidence of this is much higher in those who have suffered meningitis. Meningitis is sometimes a complication of the initial MMC closure and/or vp shunt placement for hydrocephalus.

Unlike Chiari I, in which the brain develops normally in utero and afterwards, in Chiari II there appears to be a defect in the in utero development of the brain. The structure of the brain depends on the migration of certain groups of neurons from one place to another during development. In Chiari II, these migration patterns break down to various degrees, leading to a brain which shows characteristic abnormalities anatomically on MRI or CT, but may function normally. If these groups of neurons do not function normally, the patient is likely to demonstrate development delay, which in some cases can be quite severe. If the brainstem is involved in these migration abnormalities, then not only is thinking affected, but the patient may have profound problems with swallowing, gagging, and even breathing. Such patients may well require a tracheostomy and gastric tube in infancy, as well as Chiari decompression in the first year or months of life. Such patients are at increased risk of death early on, and in such a case the true problem is not external compression on the brainstem, but a poorly developed brainstem (intrinsic damage). Chiari decompression cannot help fix a poorly developed brainstem.

Fortunately, most patients with Chiari II do not fall into such an extreme situation, though most patients with Chiari II will need surgical decompression eventually. The exact timing must be individualized as there are many confounding factors. The optimal timing is chosen to preserve neurologic function, while not putting the patient at undue risk. The situation is frequently complicated by the presence of a vp shunt and the possibility of a tethered cord should be suspected and looked for as well.

Symptoms of Chiari II include headache, failure to thrive, coughing, gagging, and feeding problems, changes in gait, decline in previously stable bladder function, loss of or decline in upper extremity function (decreasing finger dexterity—loss of ability to button shirts, manipulate coins, hold a fork, etc).

If there is a history of hydrocephalus and a vp shunt is present, the shunt should be evaluated and revised if necessary. If there is hydrocephalus without a vp shunt, a shunt should be placed prior to any Chiari decompression. If a symptomatic tethered cord is discovered, it should usually be detethered prior to Chiari decompression but only after vp shunt revision. Doing either a tethered cord release (detethering) or a Chiari decompression in the setting of untreated or ineffectively treated hydrocephalus is a recipe for disaster.

Most patients with Chiari II, but not all, will need surgical intervention at some point.

Next time: Chiari Decompression Surgery

 

fiction by Edison McDaniels…
The trade paperback edition of the most amazing Civil War novel
since Cold Mountain & The Killer Angels is now available!

NOATW Print CoverNOT ONE AMONG THEM WHOLE: A Novel of Gettysburg by Edison McDaniels tells the story of the surgeons working under the most horrendous conditions imaginable: the chaos, carnage, & blood soaked tables of a battlefield hospital in the midst of the Battle of Gettysburg. It’s all here: the brutal and unrelenting chaos of battle; the terrible humanity of the operating rooms; the failures and triumphs of primitive medicine and surgery.

“This book blew me away…a really engaging book.”

“A vivid, engrossing story of battle…”

“Heart breaking, engaging, and absolutely fantastic. I would give this book 6 stars if I could.”

Download an excerpt today by clicking here.

Buy the paperback version by clicking here.

Buy the Kindle version by clicking here.