Chiari, Part 4 of 6: Chiari Decompression Surgery The 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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