Split Cord Malformation Type 1 (Bony Spur) Excision Using Microrongeur.

Split cord malformation is well documented and reported in various case series and reports in the literature. The excision of bony spur in type 1 split cord malformation is challenging due to the intricate pathologic anatomy. The standard method advocated is to excise the bony spur with the help of a high-speed microdrill and a forward cutting punch. We describe a novel method of using fine-tipped slender microrongeur, which can negotiate the narrow confines harboring the bony spur and protect the adjacent hemicords. The surgical nuances are detailed and discussed. Copyright:

Although rare, split cord malformation is widely reported in the literature. It usually occurs in isolation. It is termed as complex spina bifida if it occurs in combination with other congenital spinal anomalies. The terms “diastematomyelia” and “diplomyelia” have been substituted by split cord malformation as proposed by Pang et al.[123] It is further divided into type 1 (midline bony spur with two separate dural sacs) and type 2 (hemicords in a single dural sac separated by a rigid fibrous septum). The split cord malformation could be symmetric or non-symmetric.

The embryological basis of split cord malformation has been proposed by Pang et al.[3] The basic ontogenetic error occurs around the time when the primitive neurenteric canal closes leads to the formation of an “accessory neurenteric canal” through the midline embryonic disc. The communication and contact between yolk sac and amnion are maintained allowing mesenchymal infiltration. It causes the neural tube to split into two separate components with an intervening fibrocartilaginous or bony septum (diastematomyelia), or remain as a single dural tube with a split cord by fibrous tissues (diplomyelia). Split cord malformation presents clinically with minimal symptoms (motor, sensory, or bladder) and neurological deficits. If the neurological deficits are pronounced, the outcome is less than optimal, probably due to partial spinal cord injury. The primary aim of surgery is to prevent aggravation of neurological deficit and avoid further injury to the spinal cord.

The excision of the bony spur poses a surgical challenge.[4567] The dysraphic soft tissue (muscle, ligamentous structures, and bony abnormalities) overlying the split cord malformation, its attachment to the bony spur, three-dimensional orientation of the bony spur, and adherence of the dural sleeves to the bony spur are important considerations which need special attention during excision of the bony spur.

The bony spur may be ventrally or dorsally located and may be complete or incomplete. It may be straight or angulated attached to the vertebral body one or two levels above or below it. A three-dimensional orientation of the spur in the sagittal plane can be obtained on CT scan prior to surgery.[7] Laminectomy is done from lateral to medial leaving the middle part attached to the spur. Drilling is done with a high-speed small-sized diamond microdrill in the direction of the spur, taking care not to injure the dura or spinal cord. A forward cutting rongeur no. 1 is used in neonates. Alternatively, the bony spur is excised using a pneumatic drill initially till the thinned-out portion is reached which is then removed with a forward cutting punch. Intraoperative neuromonitoring is helpful and recommended.

The standard method to remove bony spur is by drilling it and then using forward cutting punch.[4567] Although drilling of the spur is time-tested and advocated, there is a possibility of damage to the dura causing laceration, cerebrospinal fluid (CSF) leak, and spinal cord injury due to inadvertent loss of control over the drill or due to its vibrating effect on the dura.

We describe an alternative method of removing the bony spur using a fine-tipped single action bone microrongeur [Figures 1 and 2]. The dysraphic elements (muscle, ligaments, and abnormal bone formation) over the bony spur are removed cranially and caudally from lateral to medial except a small part, which is attached to the bony spur centrally to prevent inadvertent injury to the dura and CSF leak. The central bony, ligaments, and muscle over the spur are then meticulously dissected and shaved off till the bony spur is exposed completely. The excision of the spur is essentially done extradurally. The dural tube is gently retracted with the help of a microdissector to expand the space for exposing the base of the vertebral body. There is change of consistency from soft to firm as vertebral base is encountered. The dura is then reflected of the bony spur from posterior end till the attachment toward the vertebral body. The dural folds are then held gently apart with the help of bayonet holding forceps. The fine-tipped single action slender microrongeur with the tip opened is then insinuated in the space created between the bayonet holding forceps close to the bony spur firmly holding it. The tips of the microrongeur are aligned at the base formed at the attachment of the bony spur to the vertebral body. Thus the bony spur is engaged and snugly fitted around the bony spur, away from the dural folds on either side [Figures 1 and 2]. With a side-to-side and rotating motion, the spur is detached from the base of the vertebral body and removed enbloc. The ensuing venous bleeding from the venous plexuses is immediately controlled with heavy bone wax application. Arterial bleeding is secured with bipolar coagulation. The CSF within the dural sacs on either side acts as a buffer absorbing the jarring effect while manipulation prevents any pressure transmission on the spinal cord. The dura is then opened above and below the spur close to the midline in an elliptical manner around the sleeve of the spur. The ventral dural margins in the midline in front of the two hemicords are sutured to achieve a watertight closure.

Figure 1

Fine-tipped cutting bone rongeur. (A) Open view. (B) Closed view (tips approximated)

Figure 2

Bony spur excision. (A) Coronal CT reconstruction scan showing the lumbar bony spur. (B) Axial CT reconstruction showing the bony spur vividly. (C) Sagittal MR image showing the complex spinal dysraphism. (D) Fine-tipped bone rongeur holding the spur intoto. (E) Bony spur excised enbloc

The fine-tipped single action microrongeur is peculiar in design and action. It is slender and has delicate jaws which help to navigate in the narrow confines between the hemicords. The slight curvature of the jaws makes this instrument useful in these challenging areas as well. The blades are sharp, which when squeezed together pinch or cut the bone clean. The leaf spring between the handle opens when the hand pressure is released. It repeatedly cuts without manually reopening. The advantages of the fine tipped microrongeur are manifold. It is simple and easy to use. There are no complex maneuvers or mechanism involved. The microrongeur has to be close to the bony spur at all times and avoid dura, a precaution to prevent inadvertent injury to the dural sacs and spinal cord. The entire bony spur is secured and under control. Precision of hand movement directed on a defined area over the base of the spur ensures its complete removal. The instrument is inexpensive and easily available.

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The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.