As previously discussed, the factors that your doctor takes into consideration in planning an operation for CM
with or without syringomyelia would be:
1. The presence or absence of hydrocephalus (increased fluid within the cavities of the brain).
2. Whether or not bony abnormalities exist at the base of the skull, such as basilar invagination or
reduction in the size of the posterior fossa, and whether or not there is distortion of the CSF space at
the foramen magnum.
3. The stability of the cranio-vertebral junction (CVJ). This may require imaging of this region with the
head moved in the flexed (leaning forward) position and the extended (leaning backward) position, if
the doctor is suspicious of instability.
4. The presence of SM or its extension into the brainstem, called syringobulbia.
5. Whether a previous operative procedure was performed, such as a posterior fossa decompression, and
whether any syrinx shunt operations were performed.
These factors will guide your physician in making a surgical judgment.
GOALS OF SURGERY
It is more or less recognized that the operative procedure for CM and SM is a posterior fossa (back of skull) craniotomy (opening) with possible removal of the upper-most portion of C1 (cervical laminectomy of the first cervical vertebra). The aim of the operation is to return the cerebrospinal fluid (CSF) circulation to as close to normal as possible, thus achieving relief of symptoms; correction of the impaction or compression of the brainstem by the descending cerebellar tonsils, and deflation or shrinkage of the syrinx. In addition, one of the goals of the operation is prevention of recurrent problems and to arrest progression of problems in the future. Hence, the factors described above come into play, such as instability and presence of the bony abnormalities as well as the potential for scarring.
IMAGING PRIOR TO SURGERY
Your physician may require x-rays of the neck and the skull to visualize the anatomy and stability. As discussed in the previous chapter, the MRIs may be a standard type, or may also include one which is done with the neck in flexed and extended positions, or may evaluate the CSF flow (cine scan). If hydrocephalus is present, this requires treatment prior to embarking on any further management. Fortunately, this occurs in only a very small number of patients. In the absence of hydrocephalus, the physician then looks to see whether there are bony abnormalities at the base of the skull or upper cervical spine.
At times, the surgeon may also request a CT scan in different positions to look for bony abnormalities at the base of the skull or upper cervical spine. When such abnormalities produce bony compression and symptoms related to this may be relieved with positioning of the head or with traction, the operative procedure would be a decompression of the region of the foramen magnum and potentially a fusion of the skull to the upper cervical spine. If on the other hand the bony abnormality cannot be corrected with head position or with neck traction, the compression still needs to be relieved and your physician may elect to perform surgery from a front approach or from a side approach. The anterior, or lateral, decompression is then followed by the traditional operation from behind for the associated “Chiari”
problem, and possibly a fusion.
In the absence of bony abnormalities, the presence of CM, with or without syringomyelia (85% of patients), would require suboccipital craniectomy (enlarging the foramen magnum by creating an opening at the back of the skull) to relieve the pressure, to give more room for circulation of CSF and to relieve direct pressure on the brainstem. Many times this may be associated with removal of the back portion of the first cervical vertebra (C1 laminectomy). The need for doing an operation inside the covering of the brain and spinal cord is called an intradural procedure. Many neurosurgeons feel that this is essential to ensure the outflow of CSF from around the brain into the spine as well as to get ride of any scar tissue. Placing a dural graft creates a more generous space for the fluid to circulate.
The surgeon sometimes uses ultrasound during the operation to assist with the detection of any further
abnormalities and also to see the flow of CSF as well as its pulsations. This also gives an indication of the descent of the cerebellar tonsils and the extent of compression. The ultrasound can help to visualize relationships between the bone as well as the brainstem and the cerebellum. Some neurosurgeons will use an operating microscope. It is the surgeon’s decision whether or not to shrink the cerebellar tonsils. A dural graft may be obtained from pericranium (a layer of deep scalp tissue just outside the skull), from the covering of neck muscle or muscle from the thigh called fascia lata, or even a substitute material such as Gore-Tex. The surgeon then closes the wound in a layered fashion. In a small number of patients, a posterior fusion procedure may be required. Whether or not an internal shunt is placed would be at the discretion of the treating physician and the abnormalities encountered.
WHAT CAN I EXPECT IMMEDIATELY FOLLOWING SURGERY?
Your neurosurgeon may consider using a long-acting local anesthetic into the muscles and the nerves in the neck to delay the onset of pain. Pain control is also obtained by using intravenous (IV) medications that go directly into the IV tubing. This may be patient controlled and is usually done in a manner in which an overdose cannot occur. At times, the surgeon may recommend a soft collar for comfort. Medications such as a muscle relaxant (Robaxin) and pain medication taken by
mouth may be prescribed postoperatively. Ice packs and a collar for comfort may be recommended.
It is important to stay away from strenuous physical activities for at least three months to allow for proper healing of the neck musculature. This would include heavy lifting, avoidance of contact sport activities, using a trampoline and avoiding roller coaster rides. It is important to make sure that one has regular and soft bowel movement; straining can be avoided by the use of gentle laxatives and increased fluid intake. Some physicians may also wish to have the patient avoid bending from the waist. In children, scoliosis can be a presenting symptom in at least 15-20% of patients. It is important to stay away from strenuous physical activities for at least three months to allow for proper healing of the neck musculature. This would include heavy lifting, avoidance of contact sport activities, using a trampoline and avoiding roller coaster rides. A scoliosis brace should be worn three to four weeks after the surgery.
This is essential. It is important to be able to pick up problems such as recurrence of symptoms. If symptoms do recur, this generally happens within the first two years. Many times the recurrence may be due to scar tissue formation, or late development of instability or changes that can occur as a result of the opening of the envelope (dura) of the brain. In children, it is essential to periodically obtain an MRI because of continued growth of the skull in all directions. A postoperative MRI may be requested by the
treating surgeon within the first few days and again at periodic intervals to assess the syrinx and its shrinkage or collapse.
Dyste GN, Menezes AH: Presentation and Management of Pediatric Chiari
Malformations without Myelodysplasia. Neurosurgery 23: 589-597, 1988
Menezes AH: Chiari I Malformations with Syringohydromyelia: Database analysis
with Implications for Current Controversies. Child’s Nervous System, 14(8): 414,
Menezes AH, Muhonen MG, Piper JG, Sawin PD: Chiari Malformation Database
Report: Long-term Follow-up Review of Surgical Treatment Modalities.
Neurosurgery 80: 383A, 1994