Todd D. McCall

Comparison of low back fusion techniques: transforaminal lumbar interbody fusion (TLIF) or posterior lumbar interbody fusion (PLIF) approaches

The authors review and compare posterior lumbar interbody fusion (PLIF) with transforaminal lumbar interbody fusion (TLIF). A review of the literature is performed wherein the history, indications for surgery, surgical procedures with their respective biomechanical advantages, potential complications, and grafting substances are presented. Along with the technical advancements and improvements in grafting substances, the indications and use of PLIF and TLIF have increased. The rate of arthrodesis has been shown to increase given placement of bone graft along the weight-bearing axis. The fusion rate across the disc space is further enhanced with the placement of posterior pedicle screw–rod constructs and the application of an osteoinductive material. The chief advantages of the TLIF procedure compared with the PLIF procedure included a decrease in potential neurological injury, improvement in lordotic alignment given graft placement within the anterior column, and preservation of posterior column integrity through minimizing lamina, facet, and pars dissection.

Vertebroplasty and kyphoplasty: a comparative review of efficacy and adverse events

Vertebroplasty and kyphoplasty have become common surgical techniques for the treatment of vertebral compression fractures. Vertebroplasty involves the percutaneous injection of bone cement into the cancellous bone of a vertebral body with the goals of pain alleviation and preventing further loss of vertebral body height. Kyphoplasty utilizes an inflatable balloon to create a cavity for the cement with the additional potential goals of restoring height and reducing kyphosis. Vertebroplasty and kyphoplasty are effective treatment options for the reduction of pain associated with vertebral body compression fractures. Biomechanical studies demonstrate that kyphoplasty is initially superior for increasing vertebral body height and reducing kyphosis, but these gains are lost with repetitive loading. Complications secondary to extravasation of cement include compression of neural elements and venous embolism. These complications are rare but more common with vertebroplasty. Vertebroplasty and kyphoplasty are both safe and effective procedures for the treatment of vertebral body compression fractures.

Cervical catheter tip placement for intrathecal baclofen administration.

OBJECTIVE:Intrathecal baclofen can reduce congenital and posttraumatic spasticity. Traditionally, the catheter tip for baclofen delivery is placed in a low thoracic position, which can result in a lumbar-to-cisternal cerebrospinal fluid baclofen concentration gradient. We investigated whether more rostral catheter placement was technically feasible, safe, and able to control upper extremity spasticity. METHODS:The records of 48 patients with a baclofen pump were reviewed retrospectively to evaluate the safety and efficacy of cervically placed intrathecal catheters for baclofen administration. Twenty-three patients had a catheter located in a cervical position and 25 had a catheter in a thoracic position (control group). Complications, including baclofen overdose, mechanical failures, and infections, were noted. Pre- and postoperative Ashworth scores were determined by a physical therapist using a standardized protocol. RESULTS:The mean duration of the follow-up period was 10 months. The groups were not significantly different in patient age, baclofen dose, or duration of follow-up, but differed somewhat in the causes of spasticity. For patients with a cervical catheter tip position, upper extremity Ashworth scores decreased significantly from 4.0 ± 0.8 (standard deviation) preoperatively to 3.0 ± 0.9 postoperatively (P = 0.003). In both groups, lower extremity spasticity was significantly reduced. Postoperatively, one patient with a cervical catheter developed aspiration pneumonia, possibly because of sedation. Other complications included hardware infections, mechanical malfunctions, and pseudomeningoceles. CONCLUSION:In this series, placement of intrathecal baclofen catheters in the cervical region resulted in equal control of spasticity in the upper and lower extremities and did not increase complications related to the catheter position.

Apoptosis Suppression by Somatic Cell Transfer of Bcl-2 Promotes Sonic Hedgehog–Dependent Medulloblastoma Formation in Mice

Medulloblastomas are malignant brain tumors that arise in the cerebellum in children. Aberrant activation of the Sonic hedgehog (Shh) signaling pathway, which normally stimulates proliferation of granule neuron precursors (GNP) during cerebellar development, induces tumors in mice that closely mimic human medulloblastomas. Shh-dependent medulloblastoma formation is enhanced by hyperactive insulin-like growth factor (IGF) signaling and ectopic expression of Myc oncogenes. This enhanced tumorigenesis stems from the sensitivity of GNPs to IGF and Myc levels in regulating proliferation. An emerging theme in cancer research is that oncogene-induced cell proliferation cannot initiate neoplastic transformation unless cellular programs that mediate apoptosis are disabled. Here, we report a high frequency of medulloblastoma formation in mice after postnatal overexpression of the antiapoptotic protein Bcl-2 in cooperation with Shh. Ectopic expression of Bcl-2 alone or in combination with N-Myc did not induce tumors, indicating that Shh has essential transforming functions in GNPs not supplied by the mitogenic stimulus of N-Myc combined with a strong antiapoptotic signal provided by Bcl-2. Expression of endogenous Bcl-2 was not up-regulated in Shh-induced tumors. Instead, elevated levels of phosphorylated Akt were found, suggesting that activated phosphatidylinositol 3-kinase signaling is one intrinsic mechanism for suppressing apoptosis in Shh-dependent medulloblastomas. Thus, blockade of apoptosis cooperates with Shh-stimulated proliferation to transform GNPs and induce aggressive medulloblastomas. These findings provide insights into the molecular signals that initiate medulloblastoma formation and they support the importance of blocking apoptosis in carcinogenesis.

The cervical end of an occipitocervical fusion: A biomechanical evaluation of 3 constructs - Laboratory investigation

OBJECT Stabilization with rigid screw/rod fixation is the treatment of choice for craniocervical disorders requiring operative stabilization. The authors compare the relative immediate stiffness for occipital plate fixation in concordance with transarticular screw fixation (TASF), C-1 lateral mass and C-2 pars screw (C1L-C2P), and C-1 lateral mass and C-2 laminar screw (C1L-C2L) constructs, with and without a cross-link. METHODS Ten intact human cadaveric spines (Oc-C4) were prepared and mounted in a 7-axis spine simulator. Each specimen was precycled and then tested in the intact state for flexion/extension, lateral bending, and axial rotation. Motion was tracked using the OptoTRAK 3D tracking system. The specimens were then destabilized and instrumented with an occipital plate and TASF. The spine was tested with and without the addition of a cross-link. The C1L-C2P and C1L-C2L constructs were similarly tested. RESULTS All constructs demonstrated a significant increase in stiffness after instrumentation. The C1L-C2P construct was equivalent to the TASF in all moments. The C1L-C2L was significantly weaker than the C1L-C2P construct in all moments and significantly weaker than the TASF in lateral bending. The addition of a cross-link made no difference in the stiffness of any construct. CONCLUSIONS All constructs provide significant immediate stability in the destabilized occipitocervical junction. Although the C1L-C2P construct performed best overall, the TASF was similar, and either one can be recommended. Decreased stiffness of the C1L-C2L construct might affect the success of clinical fusion. This construct should be reserved for cases in which anatomy precludes the use of the other two.

Use of resorbable collagen dural substitutes in the presence of cranial and spinal infections—report of 3 cases

BACKGROUND Various allografts, xenografts, and synthetic materials are used in neurosurgery to repair dural defects when primary suture closure is impossible and autologous grafts are inadequate or inaccessible. When used in contaminated or infected wounds, however, nonautologous grafts promote chronic colonization and recurring infection. Recently, several resorbable dural substitutes that are broken down biologically and replaced by autologous tissues have been introduced. These include type 1 collagen matrix (DuraGen, Integra LifeSciences, Plainsboro, NJ) and a collagen implant derived from bovine skin (Durepair, Medtronic, Inc, Minneapolis, Minn), which can be applied as sutured or sutureless onlay grafts. The safety and efficacy of this material has not been reported in the setting of wound contamination or infection. CASE DESCRIPTIONS We present 3 cases in which these new collagen dural substitutes were successfully used to close dural defects in the presence of wound contamination and infection. In one case, a lumbar dural defect was closed with DuraGen in the presence of a subdural empyema. In the second case, maceration of the cranial dura mater from extensive compound depressed skull fractures was repaired with DuraGen in the presence of a subgaleal abscess. In the third case, a large dural defect in the setting of frontal osteomyelitis was successfully closed with sutured Durepair. In all cases appropriate antibiotic coverage was provided for the infection, and the tissues healed with excellent biologic incorporation and without evidence of further infection. CONCLUSIONS Resorbable collagen dural grafts appear to be effective alternatives to either primary dural closure or the use of autologous-harvested tissue grafts in the setting of grossly contaminated or infected wounds.

Inflammatory pseudotumor of the cavernous sinus and skull base.

Inflammatory pseudotumor is a non-neoplastic process of unknown etiology characterized by a proliferation of connective tissue with an inflammatory infiltrate. Intracranial inflammatory pseudotumors classically involve the cavernous sinus but can also occur in the supratentorial or infratentorial compartments and spinal canal. Symptoms are dependent on location, and, when present in the cavernous sinus, typically include cranial nerve palsies of those nerves in the cavernous sinus. These lesions are rapidly responsive to steroid therapy. Surgery is typically indicated for biopsy only, but complete resection may be justified for lesions outside the cavernous sinus.

Development and rapid growth of a desmoid tumor in the surgical corridor after suboccipital craniotomy for recurrent low-grade astrocytoma

Desmoid tumors are histologically benign but locally invasive tumors that can occur in the head and neck. We present the rare case of a desmoid tumor that occurred in the surgical corridor after suboccipital craniotomy for recurrent low-grade astrocytoma. A 30-year-old woman underwent a repeat suboccipital craniotomy for recurrent low-grade astrocytoma. A gross total resection was achieved. Nine months later, a firm, palpable mass was noted near the surgical scar. No new neurologic deficits were noted on exam. A magnetic resonance imaging scan demonstrated a homogeneously enhancing lesion superficial to the dural graft. Surgical resection of the lesion was performed through the original midline incision. The mass was resected en bloc. Histology demonstrated clear surgical margins and a tumor of low cellularity consistent with a desmoid tumor. Desmoid tumors should be considered in the differential diagnosis for superficial masses occurring in the surgical bed after posterior cervical surgery.

Symptomatic occipitocervical paracondylar process: Case report

A paracondylar process is a bony exostosis that arises from the skull base lateral to the occipital condyle and extends inferiorly toward the transverse process of the atlas. This congenital anomaly can vary in size from a small protuberance to an elongated process articulating with an epitransverse process arising from C-1. Typically, a paracondylar process is an incidental finding described in anatomical studies. The authors report on a patient with a symptomatic paracondylar process articulating with an epitransverse process that caused occipitocervical pain. Resection of the paracondylar and epitransverse processes completely relieved the patients pain.