4. Spinal dysraphisms can produce clinical signs and symptoms via structural abnormalities, mass effect from the lesion, or tethering of the spinal cord.

5. Surgical repair of spinal dysraphisms usually requires intraoperative motor and sensory nerve root mapping, therefore muscle paralysis should be spared to facilitate neuromonitoring.

6. Risk of bleeding and venous air embolization is greater in patients with larger cranial defects.

7. Thermoregulation is important in patients with spinal and cranial dysraphisms because of potential fluid losses and possible dysfunctional autonomic control.

I. Spinal dysraphisms. Spinal dysraphisms are lesions where the dorsal midline structures fail to fuse during embryogenesis. Spinal dysraphisms are categorized into two types: Spina bifida aperta (open) or spina bifida occulta (occult). Spina bifida aperta is easily identifiable by the sac-like lesion containing meninges (meningocele) or neural tissue and meninges (myelomeningocele). As the name implies, spina bifida occulta are more difficult to recognize because they often do not have cutaneous manifestations. Rachischisis consists of exposed neural tube with no covering.

II. Spina bifida aperta

A. Background and anatomy

1. Neural tube defects occur secondary to failure of the posterior neural tube to close. Closure of the neural tube begins at gestational age 22 to 23 days, with complete closure around days 26 to 27 [1]. Closure starts near the cervical spine region and extends cephalad and caudad. Therefore, most commonly defects occur along the thoracic or lumbosacral region, but can occur along the cervical region as well.

a. A meningocele consists of a herniation of meninges through the defect.

b. A myelomeningocele consists of a herniation of meninges and spinal cord elements through the defect.

2. The incidence of neural tube defects is approximately 2 to 5/1,000 live births [2].

3. These lesions are associated with Arnold–Chiari malformations, hydrocephalus, and neurologic deficits. Cervical cord or brainstem compression is possible in patients with concomitant Arnold–Chiari malformations.

4. There is no association with congenital cardiac anomalies.

5. Patients may have poor autonomic control below level of the defect.

B. Surgery

1. After birth, defects are usually covered with sterile, saline-soaked gauze [3]. The patient is typically positioned prone to avoid pressure on the defect.

2. Timely surgical closure is important to reduce risk of infection [4].

3. Occasionally, rotational or myocutaneous flaps are required for closure [4].

C. Anesthetic considerations

1. Preanesthetic evaluation

a. The antenatal history, birth history, prematurity, other comorbidities and congenital anomalies should be thoroughly reviewed prior to surgery.

b. One should document any preoperative neurologic deficits.

1

c. Latex precautions/avoidance is essential to prevent early sensitization in this vulnerable patient population.

2. Monitoring and intraoperative management

a. Standard ASA monitors include ECG, noninvasive BP, pulse oximeter, and core temperature. An arterial line may be appropriate based on other comorbidities.

2

b. Ensure adequate peripheral or umbilical IV access for fluid replacement or blood transfusion. The size of the defect affects volume of insensible fluid losses during surgery; thus, the larger the defect, the larger the volume of fluid loss expected. Typically, blood loss during the procedure is not significant enough to necessitate blood transfusions.

c. May consider inhalation or IV induction with muscle relaxant for intubation. A presumed difficult airway may warrant an awake intubation, in which case preoxygenation and atropine premedication prior to laryngoscopy may be useful.

3

d. Positioning patient for laryngoscopy may be challenging given the size of defect. Lateral decubitus position of patient may be necessary to accommodate both the defect and the laryngoscopy. If patient is supine, padding is necessary to avoid pressure or compression on the defect.

e. Prone positioning for the surgery requires careful padding to prevent increased abdominal pressure, and to protect eyes and pressure points.

f. Thermoregulation is important in this neonate population and can be achieved with forced-air warming blankets, warming lights, hot water warming mattresses, increased ambient temperature, and/or humidified inhalational agents.

3. Postoperative management

a. Common complications after closure include cerebral spinal fluid (CSF) leak, infection, poor wound healing, hydrocephalus, and tethered cord syndrome (TCS).

b. Some patients return for VP shunt secondary to hydrocephalus.

c. TCS occurs in 15% to 20% of patients during their lifetime [3] and such patients return for surgical untethering.

III. Spina bifida occulta

A. Background

1. Spina bifida occulta is a bit of a misnomer since some of these lesions have intact vertebral bodies. A better way to describe this constellation of disorders is occult spinal dysraphisms (OSD). There are over a dozen disorders that are classified as OSDs.

a. Examples of OSDs include thickened filum terminale, lipomyelomeningocele, split cord malformations (SCMs), dermoid sinus, inclusion cyst, and terminal syringohydromyelia.

b. Since all OSDs share a common embryologic origin, patients with one form of OSD can also express other forms of OSD as well [5].

2. Advances in magnetic resonance imaging (MRI) have allowed for a better understanding of OSD; there have been three important observations made:

a. Most neurologic symptoms come from tension caused by traction on the spinal cord, TCS, which will be discussed later.

b. There is a steady progression of neurologic compromise with time.

c. Once a neurologic deficit occurs, it is usually irreversible [6].

B. Anatomy/pathophysiology

1. Patients with OSD often have skin covering over their underlying pathology. These patients can also present with neurologic, orthopedic, urologic, and cutaneous lesions.

2. There are a number of cutaneous lesions that are associated with OSD. Most cutaneous lesions are found at the midline in the lumbosacral region corresponding to the level of the OSD. Common cutaneous manifestations are hypertrichosis (tuft of hair), capillary hemangioma (nevus), dermal sinus, subcutaneous lipoma, and pseudotail.

a. A popular misconception is that cutaneous lesions are a predictor for OSD. This clinical correlation is only found in 3% of the patients with cutaneous lesions. However, having two cutaneous lesions raise the predictive value to 70% [7].

b. In infants, cutaneous manifestations are often the only sign of OSD. However, as the child gets older, other manifestations will appear. These include scoliosis, vertebral abnormalities, foot deformities, lower extremity asymmetry, neurogenic bladder, abnormal reflexes, pain, and delayed motor skills.

4

3. There are three mechanisms by which OSDs produce clinical signs and symptoms:

a. The lesion itself can be an abnormal neural structure.

b. The lesion may cause a mass effect.

c. The lesion may tether the spinal cord. Tethering of the spinal cord is the primary reason that most OSDs cause neurologic deficits. The cord can be tethered cranially, caudally, ventrally, or dorsally [5].

4. The most common OSDs that occur include filum terminale, lipomyelomeningoceles, intramedullary lipomas, SCMs, and congenital dermoid sinus.

a. The filum terminale is normally a thread-like structure that connects the lower end of the spinal cord to the bony spinal column. A thickened filum terminale results in tethering of the spinal cord and is associated with a low conus. Surgical resection is usually required.

b. Lipomyelomeningoceles are fibrolipomatous masses that can extend from the intramedullary canal to the skin. They are associated with unfused vertebral bodies.

c. Intramedullary lipomas are closely related to lipomyelomeningoceles. These lipomas originate in the conus and do not extend beyond the dura. Both lipomyelomeningoceles and intramedullary lipomas grow and can create a mass effect as well as a tethered effect on the spine.

d. SCMs are a condition in which the spinal cord is split at the end. These two entities that were classically referred to as diastematomyelia and diplomyelia have now been renamed SCM I and SCM II, respectively, based on unified theory of embryogenesis. SCMs usually result in TCS [8].

e. Congenital dermoid sinuses result from the abnormal adhesion between the ectoderm (destined to form the neural tube) and the dermis. When cells from the dermis are trapped beneath the skin, it creates an epithelial lined track which may extend anywhere from the skin to the spinal cord.

(1) The primary concern is risk for infection.

(2) Dermoid cysts are formed by the same mechanism and can cause TCS or create a mass effect on the spinal cord.

(3) Dermoid sinus tracts are found in the lumbosacral region or higher. Dimples in the lower sacrum are not associated with dermoid sinuses. Probing the sinus tract or injecting radiopaque contrast is not recommended. Instead, MRI is the study of choice.

5. Diagnosis of OSD and determining the extent of the disease is highly dependent on MRIs. Prenatal ultrasonography, amniocentesis, and amniotic alpha-fetoprotein have all proven to be poor diagnostic tools for the disease. Very often, the diagnosis of OSD is missed at birth because of the lack of clinical findings. As a result, the incidence of OSD is not known [5]. However, with improved neonatal screening and better radiologic imaging, the diagnosis of OSD is being made more frequently. Females are twice as often likely as males to have OSD. There are no known environmental causes of OSD; however, there appears to a higher incident between siblings than when compared to the general public.

C. Anesthetic considerations

1. Preanesthetic evaluation

a. The most important issue is to determine, preoperatively, whether the OSD is causing traction on the spinal cord. A reliable history and physical examination can help make the diagnosis, otherwise a recent MRI may be required.

b. It is also important to determine if the patient has any evidence of scoliosis, neurogenic bladder, incontinence, positional limitations, spasticity, back pain, or leg pain. Sometimes the excision of the OSD can aggravate the aforementioned conditions.

2. Monitoring and intraoperative management

a. For simple OSD repairs, it is appropriate to use any standard anesthetic technique. If patients are placed in a prone position, pressure points should be appropriately padded. Placing bolsters so the patient’s abdomen hangs freely will improve ventilation and decreases venous engorgement of the spine.

b. Complex OSD repairs will often require intraoperative monitoring of electromyography (EMG), somatosensory (SSEPs), and motor evoked potentials (MEPs).

5

(1) If neuromuscular relaxants are used for induction, they should not be redosed if EMGs and MEPs are being measured. Volatile anesthetics should be limited to 0.5 mean alveolar concentration (MAC). Opioids have a minimal effect on action potentials; therefore, fentanyl or remifentanil infusions are popular techniques.

(2) Bite blocks should be placed if MEPs are being used.

(3) Intraoperatively, some surgeons may give high-dose steroids because of supporting data from spinal cord trauma [9].

(4) Placement of a foley catheter may be necessary for patients with neurogenic bladders.

c. Patients with OSDs who are having a procedure unrelated to their OSD should not undergo a lumbar neuraxial block for uncomplicated pain management. The low position of the conus may put the patient at risk for spinal cord injury. In addition, many of these patients do not have a normal epidural space, which may increase the risk of wet spinal taps.

d. Some anesthesiologists feel it is acceptable to place caudal epidural blocks with ultrasound guidance in patients with sacral dimpling [10]. However, it should be remembered that patients with OSDs can have abnormal sacral anatomy and that there is evidence to show that patients with tethered cord can develop cord ischemia when the spine is flexed [11]. Therefore, it may be best to conclusively rule out both of these conditions before proceeding with caudal epidural blocks.

3. Postoperative management

a. Patients should lay flat to decrease the orthostatic pressure of CSF on the dural closure. While the adult population may require large doses of opioids postoperatively, this is generally not the case in the pediatric population after OSD surgery [5].

CLINICAL PEARL

• For complex OSD repairs, intraoperative monitoring of EMGs, SSEPs, and MEPs are often required. Therefore neuromuscular blockade should be avoided.

• Patients with OSDs who are having a procedure unrelated to their OSD should not undergo a lumbar neuraxial block for uncomplicated pain management.

• In the pediatric population, there is generally not as great of an opioid requirement after an OSD repair compared to the adult population.

Only gold members can continue reading. Log In or Register to continue