Tuesday, September 4, 2007

Myelomeningocele (MMC) Repairs

Myelomenigoceles are just one of the many types of spinal dysraphism. Spinal dysraphism refers to incomplete closure of either one or more of the vertebral arches of the spine or abnormalities of the spinal cord. The lesions may be open (without skin coverage) or closed (with skin coverage). Synonyms include neural tube defect (NTD) or spina bifida. Historically the term spina bifida has been used. Technically, the term spina bifida only describes the bony defect that is not present in all types of spinal dysraphisms. Some experts feel the term should no longer be used. For a very nice summary of a "Clinician's Guide to Terminology Related to Open Spinal Defects" go here. Photo credit

Myelomeningocele (MMC) comprises 98.8% of open spinal dysraphisms and affects 70,000 people in the United States. The overall incidence of MMC is 0.2 to 0.4 per 1000 live births. For a really good overview of Spinal Dysraphism embryology, etiology, prenatal testing and diagnostic imaging please read this MedScape article: Part 2: Examining the Newborn With an Open Spinal Dysraphism written by M. Colleen Brand, RNC, MSN, NNP.

If the diagnosis of MMC is made prenatally, counseling and a planned cesarean delivery are preferred. Optimally, the delivery will be scheduled in a center where there is a neurosurgeon who specializes in the care of children. Once a child is born with MMC a thorough physical examination must be conducted to look for associated conditions that in particular might affect the surgical procedure, such as pulmonary or cardiac abnormalities. Radiographic evaluation with spinal films, cranial and renal sonograms is important, but need not delay surgical intervention. The timing of surgery is important because there is an association with delay of surgery and an increase in the infection rate. The sooner the surgical closure can be done safely after birth the better. It should not be delayed unless there are medical conditions that would prevent administration of a general anesthetic and/or the surgical procedure.

In the interval between birth and surgical intervention, the open MMC defect should be gently covered with sterile saline–soaked gauze. A simple was to do this is to wrap a kerlix gently around the torso and then soak it with sterile saline over the MMC site only. The infant should be positioned prone or laterally to avoid pressure on the placode (any spinal cord elements) prior to surgery. Intubation (I won't presume to tell the anesthesiologist how to do there job.) needs to be done with the infant in the lateral decubitus position or with the infant supported supine so there is no pressure on the defect. This can easily be managed by cradling the child in the forearms laterally on the torso. A latex-free (these babies often develop Latex Allergies) Foley catheter should be placed prior to surgery to simplify nursing care postoperatively. This allows the patient to be in the prone position postoperatively without the risk of bladder distention going unrecognized in the perioperative period.

Most MMC repairs involve only neurosurgeons. Only 10-26% involve plastic surgeons in the skin/wound coverage. The neurosurgeons always do the complex repair of the spinal cord elements. Once the neuro-elements are repaired and closed, the next layer to be addressed is the muscle closure. It is essential to achieve a good muscle closure in all cases. If the lesion is small, adequate muscle can often be obtained by making lateral releases in the paraspinal muscles on either side and approximating the muscle in the midline. For larger defects, the paraspinal and latissimus dorsi muscles may both be used, taking care to leave an adequate layer of muscle (latissimus dorsi) in situ to preserve the muscle function of the torso. A sheet of muscle can then be flapped down over the entire defect and sewn in place with 2-0 vicryl.

Once the muscle has been closed, the skin is now examined to allow for a primary closure. The skin can be dissected bluntly from the underlying tissue laterally, caudally, and superiorly as needed. All intermediate and abnormal tissue should be excised from the skin margins. In most cases, the skin can be closed in a simple midline closure. A good closure is provided by 3-0 vicryl in the subcutaneous tissues with a running 4-0 Monocryl for the skin. An occlusive dressing is necessary to protect the incision from accidental stool or urine contamination. The dressing is removed if it becomes soiled and/or on the 2nd or 3rd postoperative day. At that time, wound care is begun with hydrogen peroxide and Bacitracin three times daily.

Postoperatively the infant should be positioned prone while in the crib for the first 7 to 10 days to prevent stresses on the sutures. The infant can be held for feeding, nursing, therapy, and parental bonding. Care should be taken to avoid extended periods of pressure on the lateral trunk, in particular if the defect was large and the skin is taut. The use of a Foley catheter in the immediate postoperative period can be a useful adjunct because urinary retention can develop in these infants and the prone position can make it difficult for the nursing staff to detect this. The catheter is usually left in place for several days and then urological care is deferred to the pediatric urologist. It also aids in the prevention of soiling the incision with urine.

Prevention of MMC & other neural tube defects
Studies have shown that if all women who could become pregnant were to take a multivitamin with the B-vitamin folic acid, the risk of neural tube defects could be reduced by up to 70%. Folic acid is a water soluble B-vitamin that helps build healthy cells. Because it is water soluble, folic acid does not stay in the body for very long, so women need to take it every day to help reduce the risk of neural tube defects (NTD). Since half of all pregnancies in the United States are unplanned, women of childbearing age-even if they are not currently planning to get pregnant-should take 400 micrograms (mcg) of folic acid every day to reduce their risk of having a child with Spina Bifida. In addition, women who have experienced a pregnancy affected by a NTD like Spina Bifida need a larger prescription dose of 4000 (mcg) of folic acid daily when planning a pregnancy. Spina Bifida Association

References

  • Management of Spina Bifida, Hydrocephalus and Shunts by Lynne C Kramer, MD--eMedicine Article
  • Primary Closure of Open Myelomeningocele by Sarah J Gaskill, MD -- MedScape Article
  • Decision Making in Primary Surgical Repair of Myelomeningoceles; TM de Chalainm MD & others; Ann Plast Surg; 1995 Sept; 35 (3): 272-8
  • Living with Spina Bifida: A Guide for Families and Professionals by Adrian Sandler -- a Google eBook
  • Spina Bifida Association Website
  • Spina Bifida --Medline Plus
  • Management of Posterior Trunk Defects; Plastic & Reconstructive Surgery; Vol 118(3):73e-83e, September 1, 2006; Mathes, David W. M.D.; Thornton, James F. M.D.; Rohrich, Rod J. M.D.

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