14 The Surgi cal Technologist OCTOBER 2005 Cauda Equina Lipoma Resection with Spinal Cord Untethering in an Adult JEFFR EY J CORTESE, CST, BHSA ormally the spinal cord is a freely Spi nal cord anatomy moving structure within the spi- The spinal cord is a cylindrical bundle of nerve nal canal. The term “tethered spi- pathways that is 42 to 45 cm long and 2.5 cm Nnal cord” describes a condition in wide in the normal adult. Its rostral (cranial) end which the spinal cord is abnormally fastened is continuous with the brain stem, whereas the to an immovable structure, such as a lipoma, distal end forms a conical tapering, the conus vertebra, dura or skin. Although often initially medullaris. This is usually located at the border asymptomatic, any lesion that tethers the spi- of the first lumbar vertebrae. On occasion, it may nal cord puts the individual at risk of eventual reach only to the body of T12 or extend to the L2 neurological dysfunction. This dysfunction may level in the adult. From the conus medullaris, the occur during periods of axial growth in children lumbar and sacral nerve roots descend in a bun- or during periods of adipose deposition, which dle known as the cauda equina. The most termi- in the case of tethering may cause lipomatous nal portion of the spinal cord is the filum ter- structures to enlarge. Although the signs and minale. This connective tissue filament extends symptoms may include pain, most often they from the tip of the conus medullaris and attaches include loss of control of bowel or bladder, loss to the first segment of the coccyx (Figure 1). At of sensation in the feet, or motor dysfunction in birth, the conus medullaris is located near the L3 the sacral and lower lumbar segments. Surgical vertebrae; in the adult, it sits between the L1 and intervention of any of the lesions is directed at L2 vertebrae and occupies only the upper two- release of the tethering. One such case is pre- thirds of the vertebral canal. sented in this article. OCTOBER 2005 The Surgical Technol og i st 15 262 OCTOBER 2005 1 CE CREDIT Thickened filum terminale The most elementary form of tethering of the spinal cord occurs when the filum terminale is excessively thickened.2 In these cases, the filum terminale is often infiltrated with fatty tis- Conus medull ar is sue. Normally the filum is a fibrous structure that is a continuation of the arachnoid, which becomes the conus medullaris. A diameter greater than 2 mm, excluding fatty elements, is considered abnormal.5 Cauda equi na Lipoma Even though lumbosacral lipomas account for 29% of occult spinal dysraphisms, the embryo- logical development of spinal cord lipoma is not well understood.4 As in other forms of spinal dysraphism, normal elements are present, but are found in abnormal locations. One hypothe- sis is that disruption occurs during embryologi- cal development after the neural tube is formed, l i and subcutaneous fat is allowed to herniate into Thomson-De marLearn ng.©2004 the region of the neural tube. The lipomatous tis- sue fuses with the neural tissue, and the result- ing lipoma tethers the spinal cord. Tethering may result in neurological dysfunction. The frequency of fat infiltrate within the filum terminale has been identified by several authors Filum term i na le Coccyx as described by Marchiori and Firth. Emery and i l l f i l l i : iti Lendon found fat infiltrate in 4% to 6% of nor- Surg ca Techno ogy theSurgor ca Techno og stPos A Approach.Care ve mal adult subjects at postmortem. Modic et al i f Repr nted rom reported that 5% of the population exhibits this condition, and Guiffre identified the condition FIGURE 1: The 31 pairs of spinal nerves associated with in less than 2%.5 localized regions of the spinal cord produce Spinal cord external segmentation. On this basis, the spi- Symptoms anatomy. nal cord is considered to consist of 31 segments, The symptoms of adult tethered cord syndrome each of which is traversed by paired dorsal and (TCS) have been described previously by Chap- ventral root filaments (Figure 2). man.1 The predominant symptom of adult TCS is pain in the lower back and legs that is exacerbated Physiology by physical activity, particularly flexion and exten- Neurons, glia, and pia mater have their own elas- sion of the lumbar spine. In practically all-adult ticities and viscosities. The interlacing fibers of patients with TCS, lower back and leg pain is char- these tissues resist traction in the longitudinal acterized by the “three B signs.”These are: inability direction. If the traction is sufficient to stretch the to sit with their legs crossed (like Buddha);difficul- spinal cord, the viscoelasticity of each structure ty bending slightly over the sink for dishwashing, can provide some protection to neurons, and glia or the podium while preaching or teaching classes; cells and can help maintain neuronal function. 16 The Surgical Technologist OCTOBER 2005 and difficulty holding a baby or light object (5 lb or rofibromatosis, meningiomas, dermoid or less) at waist level while standing.1 epidermoid tumors Neurologic signs are motor and sensory defi- ● polyneuropathy or isolated peripheral neu- cits in the lower extremities, hyporeflexia of one ropathy or more tendons, increased urinary retention, ● incomplete forms of viral infection of the and musculoskeletal deformities. These include peripheral nerve scoliosis, hyperlordosis, and deformities of the ● Guillain-Barre lower extremities, such as atrophy, hammertoes, ● early stages of degenerating diseases and and high-arched feet.1 familial spastic paraplegia ● any disorder that causes incontinence Differential Diagnosis ● scoliosis of other etiology, such as tuberculo- Chapman described a vast array of differential sis of vertebrae and epidural space diagnoses and other possible causes of symp- ● congenital or acquired deformities due to toms that must be ruled out. These include:1 musculoligamentous or bony abnormalities, ● intrinsic spinal cord tumors (ependymomas, particularly those of the lumbar vertebrae astrocytomas) ● articular facets that cause referred pain in the ● multiple sclerosis groin, buttock, or greater trochanteric area ● lumbosacral syringomyelia ● skeletal system disorders, such as herniated ● arteriovenous malformations disc (Table 1), spondylosis, spondylolisthesis, ● poliomyelitis osteoarthritic spondylosis, and lumbar canal ● an epidural or intradural mass compressing stenosis the spinal cord, such as schwannomas, neu- FIGURE 2: Anterior view of the spinal Gray matter Filaments of dorsa l root cord. Whi te matter Anteri or med i an f i ssure l i Filaments o f ventral root Thomson-De marLearn ng.©2004 Ventral root Spi na l gangli on Spi na l nerve i l l f i l l i : iti Surg ca Techno ogy theSurgor ca Techno og stPos A Approach.Care ve i f Repr nted rom OCTOBER 2005 The Surgical Technologist 17 Imaging studies tion, the dura is found to be significantly thinner Imaging studies are useful for making the than in normal individuals. diagnosis of TCS: plain film studies, MRI, and myelography combined with CT and ultraso- Surgicaltechnique nography. Magnetic resonance imaging is cur- The surgical release of the tethered cord presents rently the most useful imaging study for patients a challenge to even the most experienced neuro- with TCS. There are several imaging clues used surgeon. Complete understanding of the anato- to help in the diagnosis: my involved and meticulous microsurgical tech- ● a thick filum terminale (>2 mm in diameter), niques are called upon. ● the presence of structures that suggest lack The goal of surgery is to release the tethered of viscoelasticity, such as fibroadipose tis- neural elements and reduce the bulk of the associ- sue in the filum terminale, and obliteration ated lipoma.1 This is more easily achieved in dor- of the subarachnoid space, which suggests sal or caudal lesions than with traditional ones. adhesion around the caudal spinal cord or With the latter, the presence of important neural nerve roots elements within the lipoma may make it impos- ● an elongated spinal cord sible to safely achieve complete untethering. ● a posteriorly displaced conus medullaris or The risk of neural injury is also affected by filum, directly attached to the posterior the- the confusing relationships between neural ele- cal lining at or near the L5 lamina ments, lipoma, and the extent of the dural defect in cases of extensive lateral asymmetry of the A capacious sacral subarachnoid space is found lesion with distortion of the conus. In such cases, in 50% of patients and is associated with posteri- there is little normal anatomy to provide the sur- or displacement of the filum.4 During the opera- geon with adequate intraoperative orientation. The surgeon must rely on neurophysiological FIGURE 3: monitoring techniques to avoid neural injury. Bipolar The patient is administered general anesthe- sia via endotracheal intubation, and a Foley cath- coagulation eter is placed. He or she is rotated into the prone of epidural position onto a well-padded operating table fitted with a Wilson frame or a similar type of device. vessels. Extreme attention is paid to the protection of all pressure points, as the surgery can last sev- eral hours. If needed, the head can be suspend- ed in a Mayfield or Sugita head-holding device to reduce the risk of direct intraocular pressure. The patient should receive 1 gram of Cefazolin, FIGURE 4: 2 grams of Solumedrol, 250 cc of 20% Mannitol, Durotomy and 40 mg of Lasix prior to the incision. Contin- uous monitoring of the somatosensory evoked started at potential (SSEP), as well as the motor evoked upper level potentials (MEP) should be employed during the resection of the lipoma due to dissection around of lipoma.