Motion preservation in cervical spine: review.

Cervical disc replacement is an innovative technology that preserves motion at the instrumented level and has evolved as a potential alternative to spinal fusion for the treatment of cervical radiculopathy and myelopathy. Despite the excellent results of anterior cervical discectomy and fusion, arthroplasty allows for motion preservation which may be beneficial. Although the initial and midterm results from the randomized clinical trials demonstrated safety and equivalent clinical success as compared to anterior cervical fusion; the evidence establishing the superiority of arthroplasty over fusion in terms of preventing adjacent segment degeneration/disease is not available at this time.

Operative treatment of cervical spondylotic myelopathy and radiculopathy. A comparison of laminectomy and laminoplasty at five year average follow-up.

BACKGROUND: The natural history of cervical spondylotic myelopathy is frequently one of slow, progressive neurological deterioration. The operative treatment for patients with moderate to severe involvement is decompression of the spinal cord. Laminectomy has been a traditional approach and laminoplasty has developed as an attractive alternative. The purpose of this study was to examine and compare the outcomes of these two procedures in similar groups of patients at a five year average follow-up. METHODS: A consecutive series of twenty patients who underwent open-door laminoplasty for multi-level cervical spondylotic myelopathy or radiculopathy was compared to a similar group of 22 matched patients who underwent multi-level laminectomies. Patients were similar in age, gender, number of operative levels, and length of follow-up. At the latest examination, each patient underwent a comprehensive neurological evaluation. A modification of the Nurick classification was used to assess the degree of myelopathy. Radiographs at latest follow-up were assessed for instability, and measurements of the space-available-for-the-cord and Pavlov ratio were made at involved levels. RESULTS: Myelopathy, as determined by our modified Nurick scale, improved from a preoperative average of 2.44 to 1.48 in laminoplasty patients and from an average of 3.09 to 2.50 in laminectomy patients. Pain improved 57 percent and 8 percent in laminoplasty and laminectomy groups, respectively. Subjective neck stiffness was not significantly different based on the numbers available, although laminoplasty patients demonstrated some loss of range of motion on examination. The only variable that predicted the postoperative degree of myelopathy in both groups was the preoperative degree of myelopathy. CONCLUSIONS: Laminectomy and laminoplasty patients demonstrated improvements in gait, strength, sensation, pain, and degree of myelopathy. Laminoplasty was associated with fewer late complications. Based on this analysis, we believe that laminoplasty is an effective alternative to laminectomy in patients with multi-level cervical spondylotic myelopathy or radiculopathy.

A finite element investigation of upper cervical instrumentation.

STUDY DESIGN: The finite element technique was used to predict changes in biomechanics that accompany the application of a novel instrumentation system designed for use in the upper cervical spine. OBJECTIVE: To determine alterations in joint loading, kinematics, and instrumentation stresses in the craniovertebral junction after application of a novel instrumentation system. Specifically, this design was used to assess the changes in these parameters brought about by two different cervical anchor types: C2 pedicle versus C2-C1 transarticular screws, and unilateral versus bilateral instrumentation. SUMMARY OF BACKGROUND DATA: Arthrodesis procedures can be difficult to obtain in the highly mobile craniovertebral junction. Solid fusion is most likely achieved when motion is eliminated. Biomechanical studies have shown that C1-C2 transarticular screws provide good stability in craniovertebral constructs; however, implantation of these screws is accompanied by risk of vertebral artery injury. A novel instrumentation system that can be used with transarticular screws or with C2 pedicle screws has been developed. This design also allows for unilateral or bilateral implantation. However, the authors are unaware of any reports to date on the changes in joint loading or instrumentation stresses that are associated with the choice of C2 anchor or unilateral/bilateral use. METHODS: A ligamentous, nonlinear, sliding contact, three-dimensional finite element model of the C0-C1-C2 complex and a novel instrumentation system was developed. Validation of the model has been previously reported. Finite element models representing combinations of cervical anchor type (C1-C2 transarticular screws vs. C2 pedicle screws) and unilateral versus bilateral instrumentation were evaluated. All models were subjected to compression with pure moments in either flexion, extension, or lateral bending. Kinematic reductions with respect to the intact (uninjured and without instrumentation) case caused by instrumentation use were reported. Changes in loading profiles through the right and left C0-C1 and C1-C2 facets, transverse ligament-dens, and dens-anterior ring of C1 articulations were calculated by the finite element model. Maximum von Mises stresses within the instrumentation were predicted for each model variant and loading scenario. RESULTS: Bilateral instrumentation provided greater motion reductions than the unilateral instrumentation. When used bilaterally, C2 pedicle screws approximate the kinematic reductions and instrumentation stresses (except in lateral bending) that are seen with C1-C2 transarticular screws. The finite element model predicted that the maximum stress was always in the region in which the plate transformed into the rod. CONCLUSIONS: To the best of the authors' knowledge, this is the first report of predicting changes in loading in the upper cervical spine caused by instrumentation. The most significant conclusion that can be drawn from the finite element model predictions is that C2 pedicle screw fixation provides the same relative stability and instrumentation stresses as C1-C2 transarticular screw use. C2 pedicle screws can be a good alternative to C2-C1 transarticular screws when bilateral instrumentation is applied.

Cervical spinal motion during intubation: efficacy of stabilization maneuvers in the setting of complete segmental instability.

OBJECT: The purpose of this study was to characterize and compare segmental cervical motion during orotracheal intubation in cadavers with and without a complete subaxial injury, as well as to examine the efficacy of commonly used stabilization techniques in limiting that motion. METHODS: Intubation procedures were performed in 10 fresh human cadavers in which cervical spines were intact and following the creation of a complete C4-5 ligamentous injury. Movement of the cervical spine during direct laryngoscopy and intubation was recorded using video fluoroscopy and examined under the following conditions: 1) without stabilization; 2) with manual in-line cervical immobilization; and 3) with Gardner-Wells traction. Subsequently, segmental angular rotation, subluxation, and distraction at the injured C4-5 level were measured from digitized frames of the recorded video fluoroscopy. CONCLUSIONS: After complete C4-5 destabilization, the effects of attempted stabilization on distraction, angulation, and subluxation were analyzed. Immobilization effectively eliminated distraction, and diminished angulation, but increased subluxation. Traction significantly increased distraction, but decreased angular rotation and effectively eliminated subluxation. Orotracheal intubation without stabilization had intermediate results, causing less distraction than traction, less subluxation than immobilization, but increased angulation compared with either intervention. These results are discussed in terms of both statistical and clinical significance and recommendations are made.

Pathomechanisms of failures of the odontoid.

STUDY DESIGN: A finite element investigation to determine the causal mechanisms that lead to odontoid fracture. OBJECTIVES: To elucidate which loading scenarios, including rotational moments, compression-tension, and lateral and anteroposterior shear, can result in Type I, Type II, and Type III odontoid failures. SUMMARY OF BACKGROUND DATA: There is considerable controversy about the major loading path that causes odontoid fractures. A review of the clinical and laboratory research literature did not provide a consensus on this issue. METHODS: A three-dimensional, nonlinear finite element model of the occipito-atlantoaxial (C0-C1-C2) complex was generated from human cadaveric data. Force loads were applied at the posterior margin of the occiput and were applied as lone entities or after the model was prepositioned in flexion, extension, or lateral-bending moments through applied rotation moments. Intraosseous stresses were reported to characterize the probability of fracture due to the applied loadings. RESULTS: The data indicate that hyperextension can lead to failure of the odontoid at its superior tip (Type I). Finite element model predictions also demonstrated the propensity of loads that induce axial rotation to create relatively high maximum von Mises stress in the Type II fracture region. Flexion prepositioning reduced the stress response of the odontoid. CONCLUSIONS: Force loading that puts the head in extension coupled with lateral shear or compression leads to Type I fractures, whereas axial rotation and lateral shear can produce Type II fractures. The model failed to elucidate causal mechanisms for Type III fractures. Flexion seems to provide a protective mechanism against force application that would otherwise cause a higher risk of odontoid failure.

Management of cervical spinal fractures in ankylosing spondylitis with posterior fixation.

STUDY DESIGN: Introduction of a posterior approach for internal fixation of fractures of the ankylosed cervical spine. OBJECTIVES: To evaluate the clinical outcome of patients with ankylosing spondylitis and cervical spinal fractures treated with posterior instrumentation and a collar orthosis. SUMMARY OF BACKGROUND DATA: Cervical spinal fractures in patients with ankylosing spondylitis almost always extend completely across the vertebral segment to include both anterior and posterior elements. Treatment with immobilization alone is often inadequate. Generalized spinal rigidity and exaggerated thoracic kyphosis may hinder anterior exposure. Posterior approaches have been described but generally require postoperative halo immobilization. In the authors' technique for patients whose spinal alignment is relatively well preserved, a posterior exposure is used that achieves three-point internal fixation along multiple segments. The complications associated with halo immobilization are avoided. METHODS: Seven patients with ankylosing spondylitis and fractures of the cervical spine were stabilized with posterior instrumentation. Patients were immobilized after surgery with either a cervical collar or a sternal occipital mandibular immobilizing brace and observed for neurologic outcome, radiographic evidence of bony fusion, and complications. RESULTS: No patient experienced neurologic deterioration with surgery. Two patients died at acute rehabilitative facilities after discharge. Radiographic evidence of fusion was observed in the five patients available for follow-up. CONCLUSIONS: Patients with ankylosing spondylitis and cervical spinal fractures can be adequately treated with lateral mass plating and interspinous wiring of autologous rib graft. Adequate postoperative immobilization can be attained with a cervical collar and does not require a halo vest.

Biomechanical rationale for the pathology of rheumatoid arthritis in the craniovertebral junction.

STUDY DESIGN: A finite-element model of the craniovertebral junction was developed and used to determine whether a biomechanical mechanism, in addition to inflammatory synovitis, is involved in the progression of rheumatoid arthritis in this region of the spine. OBJECTIVES: To determine specific structure involvement during the progression of rheumatoid arthritis and to evaluate these structures in terms of their effect on clinically observed erosive changes associated with the disease by assessing changes in loading patterns and degree of anterior atlantoaxial subluxation. SUMMARY OF BACKGROUND DATA: Rheumatoid arthritis involvement of the occipito-atlantoaxial (C0-C1-C2) complex is commonly seen. However, the biomechanical contribution to the development and progression of the disease is neither well understood nor quantified. Although previous cadaver studies have elucidated information on kinematic motion and fusion techniques, the modeling of progressive disease states is not easily accomplished using these methods. The finite-element method is well suited for studying progressive disease states caused by the gradual changes in material properties that can be modeled. METHODS: A ligamentous, nonlinear, sliding-contact, three-dimensional finite-element model of the C0-C1-C2 complex was generated from 0.5 mm thick serial computed tomography scans. Validation of the model was accomplished by comparing baseline kinematic predictions with experimental data. Transverse, alar, and capsular ligament stiffness were reduced sequentially by 50%, 75%, and 100% (removal) of their intact values. All models were subjected to flexion moments replicating the clinical diagnosis of rheumatoid arthritis using full flexion lateral plane radiographs. Stress profiles at the transverse ligament-odontoid process junction were monitored. Changes in loading profiles through the C0-C1 and C1-C2 lateral articulations and their associated capsular ligaments were calculated. Anterior and posterior atlantodental interval values were calculated to correlate ligamentous destruction with advancement of atlantoaxial subluxation. RESULTS: Model predictions (at 0.3 Nm) fell within one standard deviation of experimental means, and range of motion data agreed with published in vitro and in vivo values. The model predicted that stresses at the posterior base of the odontoid process were greatly reduced with transverse ligament compromise beyond 75%. Decreases through the lateral C0-C1 and C1-C2 articulations were compensated by their capsular ligaments. Anterior and posterior atlantodental interval values indicate that the transverse ligament stiffness decreases beyond 75% had the greatest effect on atlantoaxial subluxation during the early stages of the disease (no alar and capsular ligament damage). Subsequent involvement of the alar and capsular ligaments produced advanced atlantoaxial subluxation, for which surgical intervention may be warranted. CONCLUSIONS: To the best of the authors' knowledge, this is the first report of a validated, three-dimensional model of the C0-C1-C2 complex with application to rheumatoid arthritis. The data indicate that there may be a mechanical component (in addition to enzymatic degradation) associated with the osseous resorption observed during rheumatoid arthritis. Specifically, erosion of the odontoid base may involve Wolff's law of unloading considerations. Changes through the lateral aspects of the atlas suggest that this same mechanism may be partially responsible for the erosive changes seen during progressive rheumatoid arthritis. Anterior and posterior atlantodental interval values indicate that complete destruction of the transverse ligament coupled with alar and/or capsular ligament compromise is requisite if advanced levels of atlantoaxial subluxation are present.

Management of type II dens fractures: a case-control study.

STUDY DESIGN: A case-control study of patients with isolated type II dens fractures treated with halo vest immobilization. OBJECTIVES: To evaluate age as a risk factor for failure of halo immobilization in patients with type II dens fractures. SUMMARY OF BACKGROUND DATA: The literature reports an average fusion rate of approximately 70% in patients with type II dens fractures treated by halo vest immobilization. Although many investigators have examined patient age as a risk factor for nonfusion using halo immobilization, all studies have been supported only by Class III data. These studies, consequently, carry little or no statistical significance. Therefore, a case-control study based on Class II data was designed to evaluate age as a risk factor for failure of halo vest immobilization in patients with type II dens fractures. METHODS: Thirty-three patients with isolated type II dens fractures treated with halo vest immobilization at the University of Iowa Hospitals and clinics between 1983 and 1997 were included. Type II fractures were defined with plain radiography as per the Anderson-D'Alonzo classification. Cases were defined as nonfusions after halo immobilization, whereas control subjects represented successful bony unions attained with halo immobilization. RESULTS: When the case and control groups were compared, there was no significant difference between the groups in the presence of concomitant medical conditions, sex, the amount of fracture displacement, the direction of fracture displacement, the length of hospital stay, or length of follow-up. Age more than 50 years was found to be a highly significant risk factor for failure of halo immobilization (P = 0.002; Fisher's exact test, two-tailed). The odds ratio of these data indicate that the risk of failure of halo immobilization is 21 times higher in patients aged 50 years or more. CONCLUSIONS: Surgical intervention should be considered in those patients aged 50 years or more who have a type II dens fracture, if it can be accomplished with acceptable risk of morbidity and death.

Segmental cervical spine motion during orotracheal intubation of the intact and injured spine with and without external stabilization.

OBJECT: The purpose of this study was to establish a cadaveric model for evaluating cervical spine motion in both the intact and injured states and to examine the efficacy of commonly used stabilization techniques in limiting that motion. METHODS: Intubation was performed in fresh human cadavers with intact cervical spines, following the creation of a C4-5 posterior ligamentous injury. Movement of the cervical spine during direct laryngoscopy and intubation was recorded using video fluoroscopy and examined under the following conditions: 1) without external stabilization; 2) with manual in-line cervical immobilization; and 3) with Gardner-Wells traction. Subsequently, segmental motion of the occiput through C-5 (Oc-C5) was measured from digitized frames of the recorded video fluoroscopy. The predominant motion, at all levels measured in the intact spine, was extension. The greatest degree of motion occurred at the atlantooccipital (Oc-C1) junction, followed by the C1-2 junction, with progressively less motion at each more caudal level. After posterior destabilization was induced, the predominant direction of motion at C4-5 changed from extension to flexion, but the degree of motion remained among the least of all levels measured. Traction limited but did not prevent motion at the Oc-C1 junction, but neither traction nor immobilization limited motion at the destabilized C4-5 level. CONCLUSIONS: Cadaveric cervical spine motion accurately reflected previously reported motion in living, anesthetized patients. Traction was the most effective method of reducing motion at the occipitocervical junction, but none of the interventions significantly reduced movement at the subaxial site of injury. These findings should be considered when treating injured patients requiring orotracheal intubation.

Granulocytic sarcoma of the spine.

OBJECTIVE: Granulocytic sarcomas (chloromas) are tumors consisting of primitive myeloid cells. They are rare manifestations of acute and chronic leukemias and can occasionally precede the development of systemic disease by weeks to years. Spinal complications of chloromas, such as cord compression secondary to epidural tumor or cauda equina syndrome, have been described but are uncommon. METHODS: We present eight new cases of spinal chloroma. Three patients displayed significant motor deficit in the form of paraparesis or paraplegia. All patients complained of lower back pain, with other complaints including generalized pain, abdominal pain, numbness and pain in the lower extremities and perianal region, and poor appetite. The average age of the patients was 37 years. Treatment strategies included surgery, chemotherapy, and radiotherapy. Three patients underwent surgical decompression. Six patients received chemotherapy, and six patients received radiotherapy at doses of 2000 to 3000 cGy in up to 30 fractions. RESULTS: Patient survival ranged from 18 days to 9.5 years after diagnosis. A review of the previously reported cases of granulocytic sarcoma in addition to our new cases reveals that the most effective treatment is multimodality therapy coupled with early diagnosis. CONCLUSION: Increased awareness of this entity will facilitate early diagnosis and minimize potentially preventable neurological morbidity.

Evidence-based analysis of odontoid fracture management.

OBJECT: The management of odontoid fractures remains controversial. Evidence-based methodology was used to review the published data on odontoid fracture management to determine the state of the current practices reported in the literature. METHODS: The Medline literature (1966-1999) was searched using the keywords "odontoid," "odontoid fracture," and "cervical fracture" and graded using a four-tiered system. Those articles meeting selection criteria were divided in an attempt to formulate practice guidelines and standards or options for each fracture type. Evidentiary tables were constructed by treatment type. Ninety-five articles were reviewed. Five articles for Type I, 16 for Type II, and 14 for Type III odontoid fractures met selection criteria. All studies reviewed contained Class III data (American Medical Association data classification). CONCLUSIONS: There is insufficient evidence to establish a standard or guideline for odontoid fracture management. Given the extent of Class III evidence and outcomes reported on Type I and Type III fractures, a well-designed casecontrolled study would appear to provide sufficient evidence to establish a practice guideline, suggesting that cervical immobilization for 6 to 8 weeks is appropriate management. In cases of Type II fracture, analysis of the Class III evidence suggests that both operative and nonoperative management remain treatment options. A randomized trial or serial case-controlled studies will be required to establish either a guideline or treatment standard for this fracture type.

Midline anterior craniofacial approach for malignancy: results of en bloc versus piecemeal resections.

Thirty consecutive cases of midline anterior craniofacial procedures for the treatment of malignant neoplasms arising from the paranasal sinuses were reviewed. Posterior and lateral base craniofacial procedures were specifically excluded. This review compares the results, in terms of survival and major complication rate, between en bloc and piecemeal resections. The average follow-up was 4 years and 3 months. Sixteen patients were treated with an en bloc resection. The major complication rate was 31%. One-year survival rate was 94% for the en bloc resection group, 67% for patients with positive margins, and 100% for patients with clear margins. Three-year survival for en bloc resection dropped to 56, 33, and 67%, respectively. Fourteen patients were treated with piecemeal resections. The major complication rate was 21%. One-year survival rate was 83% for the piecemeal resection group, 60% for patients with positive margins, and 100% for patients with clear margins. Three-year survival dropped to 70, 60, and 80%, respectively. Although it is considered desirable to obtain an en bloc resection in some craniofacial procedures, we conclude that a piecemeal resection is a viable alternative in situations where an en bloc procedure is difficult to obtain safely.

Complications of posterior articular mass plate fixation of the subaxial cervical spine in 43 consecutive patients.

STUDY DESIGN: A retrospective study evaluating the complications in 43 consecutive patients treated with posterior lateral mass plate fixation of the subaxial cervical spine. OBJECTIVES: To determine the surgical complications of applying posterior lateral mass plates, to correlate complication rate with surgical technique, and to determine fusion rate. SUMMARY OF BACKGROUND DATA: Posterior cervical plate stabilization is a viable alternative to more traditional wiring techniques. Advantages include superior internal stability and no requirement for intact posterior spinal elements. METHODS: Records of 43 consecutive patients who underwent posterior articular mass plate fixation were independently reviewed to identify associated complications. The average follow-up was 25 months (range, 1 to 63 months). The most common indications for surgery were posttraumatic instability (n = 22) and instability after multilevel laminectomy (n = 14). Four patients had difficult spinal disorders requiring a combined anterior and posterior approach. RESULTS: Two hundred eighty-one screws were inserted in the cervical spine (average, 7 screws per patient). There were no complications associated with placement of the screws (i.e., root injury or vertebral artery injury). Complications included two cases in which patients had superficial wound infections and one in which the patient had a spinal epidural hematoma requiring evacuation. In one patient, hardware failure required an anterior approach to correct a progressive angulation. CONCLUSIONS: With the authors' surgical technique, lateral mass plate fixation is safe and effective. There were no nerve root or vertebral artery injuries.

A comparative analysis of fusion rates and donor-site morbidity for autogeneic rib and iliac crest bone grafts in posterior cervical fusions.

OBJECT: Autogeneic bone graft is often incorporated into posterior cervical stabilization constructs as a fusion substrate. Iliac crest is used frequently, although donor-site morbidity can be substantial. Rib is used rarely, despite its accessibility, expandability, unique curvature, and high bone morphogenetic protein content. The authors present a comparative analysis of autogeneic rib and iliac crest bone grafts, with emphasis on fusion rate and donor-site morbidity. METHODS: A review was conducted of records and radiographs from 600 patients who underwent cervical spinal fusion procedures in which autogeneic bone grafts were used. Three hundred patients underwent rib harvest and posterior cervical fusion. The remaining 300 patients underwent iliac crest harvest (248 for an anterior cervical fusion and 52 for posterior fusion). The analysis of fusion focused on the latter subgroup; donor-site morbidity was determined by evaluating the entire group. Fusion criteria included bony trabeculae traversing the donor-recipient interface and long-term stability on flexion-extension radiographs. Graft morbidity was defined as any untoward event attributable to the graft harvest. Statistical comparisons were facilitated by using Fisher's exact test. CONCLUSIONS: Demographic data obtained in both groups were comparable. Rib constructs were placed in the following regions: occipitocervical (196 patients), atlantoaxial (35 patients), and subaxial cervical spine (69 patients). Iliac crest grafts were placed in the occipitocervical (28 patients), atlantoaxial (10 patients), and subaxial cervical (14 patients) regions. Fusion occurred in 296 (98.8%) of 300 rib graft and 49 (94.2%) of 52 iliac crest graft constructs (p = 0.056). Graft morbidity was greater with iliac crest than with rib (p < 0.00001). Donor-site morbidity for the rib graft was 3.7% and included pneumonia (eight patients), persistent atelectasis (two patients), and superficial wound dehiscence (one patient). Pneumothorax, intercostal neuralgia, and chronic chest wall pain were not encountered. Iliac crest morbidity occurred in 25.3% of the patients and consisted of chronic donor-site pain (52 patients), wound dehiscence (eight patients), pneumonia (seven patients), meralgia paresthetica (four patients), hematoma requiring evacuation (three patients), and iliac spine fracture (two patients). Even when chronic pain was not considered, morbidity encountered in obtaining iliac crest still exceeded that encountered with rib harvest (p = 0.035). The fusion rate and donor-site morbidity for rib autograft compare favorably with those for iliac crest when used in posterior cervical constructs. To the authors' knowledge, this represents the largest series to date in which the safety and efficacy of using autogeneic bone graft materials in spinal surgery are critically analyzed.

Assessment of primary and salvage lateral mass screw insertion torque in a cadaveric model.

This study was performed to determine the insertion torques of three types of lateral mass screws and to explore their relationship to bone mineral density (BMD). The peak insertion torque of primary articular screws was measured, and the holes were then stripped by overtightening. Larger diameter "salvage" screws were placed in the stripped holes, and peak insertion torque was measured. Peak primary screw insertion torque and BMD were positively correlated (r = 0.48, p = 0.00001). The ratio of salvage to primary screw insertion torque varied significantly among the systems (p = 0.0003). The positive correlation between BMD and primary screw peak insertion torque confirms the importance of bone density for satisfactory screw purchase. The large variation in the ratio of salvage to primary screw insertion torque among systems may be due to differences in primary and salvage screw design.

Increased height in patients with medulloblastomas.

OBJECTIVE: Medulloblastomas demonstrate histological features similar to neuroendocrine tumors. Expression of various receptors for growth factors and production of growth hormones have been identified to occur with medulloblastomas. We studied the preoperative height of patients with medulloblastomas. METHODS: We studied 85 patients (64 children and 21 adults) with medulloblastomas and 42 patients (27 children and 15 adults) with cerebellar astrocytomas who served as a control group. All of the patients had their height and weight documented on standardized growth charts. In addition, age, sex, symptoms, radiographic findings, treatment, and survival were examined. RESULTS: Preoperatively, 22.4% of the patients with medulloblastomas were above the 95% curve in height and 80.0% were above the 50% curve for height. Compared with patients with cerebellar astrocytomas, 7.1% were above the 95% curve for height and 54.8% were above the 50% curve for height. The distribution of patients along the weight curves for both tumor types demonstrated a slight prevalence for lower weights but was not significantly different from the national average. A significant number of patients presenting with medulloblastomas attained increased height, which was disproportionate to the weight loss generally observed with neoplasms. To our knowledge, the disproportionate number of patients with medulloblastomas and increased height has not been reported before. A similar deviation in height distribution from the normal population could not be identified in patients with cerebellar astrocytomas. CONCLUSION: This study suggests that medulloblastomas may be influenced by growth hormone production or may produce growth factors in vivo.

Idiopathic spinal epidural lipomatosis.

OBJECTIVE: Spinal epidural lipomatosis (SEDL) is a rare disorder often associated with the administration of exogenous steroids or the elevation of endogenous steroids. Spinal epidural lipomatosis develops in some patients in the absence of elevated steroid levels. The limited information known about idiopathic SEDL comes predominantly from isolated case reports. We proposed to study our experience with idiopathic SEDL and to review the literature. METHODS: We identified eight symptomatic patients with idiopathic SEDL treated at our institution, which is the largest series reported. All patients were male and obese by body mass index (> 27.5 kg/m2). The mean age of the patients was 35.4 years. Idiopathic SEDL was equally distributed between the thoracic and lumbar spine. Six patients underwent laminectomy and fat debulking with good postoperative results; two patients were treated with a weight loss diet, which resulted in the relief of symptoms after losing > 15 kg each. RESULTS AND CONCLUSION: A review of our patients in conjunction with other reported cases reveals the following: 1) idiopathic SEDL occurs almost exclusively in the obese population; 2) idiopathic SEDL seems to occur with equal frequency between the thoracic and lumber spine; 3) a strong male predominance exists; 4) thoracic SEDL presents at an earlier age compared with lumbar SEDL; 5) surgical decompression remains the treatment of choice for the immediate relief of symptoms. Our experience suggests that idiopathic epidural lipomatosis may be a pathological entity that has been underdiagnosed.