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Biomedical subjects

D G Vollmer

Publications and source records attributed to D G Vollmer.

At least 19 recordsLinked to original sources
PubMed2005

Intensity-modulated radiosurgery for childhood arteriovenous malformations.

PURPOSE: Presentation of intensity-modulated radiosurgery (IMRS) for the treatment of inoperable, complex shaped pediatric arterio-venous malformations AVM. METHOD: Between 03/99 and 11/04, IMRS was delivered to seven children aged six to 18 years. Prescribed minimum doses ranged from 17.5 to 20 Gy (median 18 Gy). Radiosurgery planning and delivery used a serial tomotherapeutic IMRT technique (Peacock IMRT, North American Scientific/Nomos, Cranberry Township, PA) over two to four couch angles. A linear accelerator attached binary multi-leaf collimator was used to generate pencil beams of 10 mm by either 8.5 or 4.0 mm. Treatment planning employed an inverse treatment planning optimization algorithm. Parameters submitted to the treatment planning system were: prescription dose (PD), volume of target allowed to receive less dose (standard 3%), minimum dose (0.5 Gy less than PD), and maximum dose (200% of PD). Planning system specific IMRS target and tissue types were selected to prioritize dose conformality over dose homogeneity. The prescription isodose encompassed at least 95% of the target volume. We calculated conformality (CI) and homogeneity indices (HI) to characterize the quality of IMRS plans, and summarized preliminary clinical outcomes. FINDINGS: Target volumes ranged from 0.71 to 63.02 cm(3) (median 13.8 cm(3), 6/7 AVM larger than 10 cm(3)). Median CI was 1.07 (range 1.05 to 1.7) according to RTOG criteria. Median HI was 1.12 (range 1.09 to 1.23). During limited follow-up (median 32 months, range 5 to 53 months), two AVM completely obliterated at 19 and 22 months, and partial obliteration (>75%) was observed in three cases. No treatment-related side effects, other than acute nausea and temporary headaches interpreted as being associated with changes in cerebral blood distribution, were observed. CONCLUSIONS: IMRS can allow for highly conformal planning and delivery of radiosurgery radiation doses even if pediatric AVM target volumes are large and/or highly complex in shape. This technique has been seen to result in favorable preliminary outcomes, thus supporting future exploration of this technique in pediatric and adult patients.

Adolescent↗
PubMed2001

The TALON removable head frame system for stereotactic radiosurgery/radiotherapy: measurement of the repositioning accuracy.

PURPOSE: To present the TALON removable head frame system as an immobilization device for single-fraction intensity-modulated stereotactic radiosurgery (IMRS) and fractionated stereotactic intensity-modulated radiotherapy (FS-IMRT); and to evaluate the repositioning accuracy by measurement of anatomic landmark coordinates in repeated computed tomography (CT) examinations. METHODS AND MATERIALS: Nine patients treated by fractionated stereotactic intensity-modulated radiotherapy underwent repeated CTs during their treatment courses. We evaluated anatomic landmark coordinates in a total of 26 repeat CT data sets and respective x, y, and z shifts relative to their positions in the nine treatment-planning reference CTs. An iterative optimization algorithm was employed using a root mean square scoring function to determine the best-fit orientation of subsequent sets of anatomic landmark measurements relative to the original image set. This allowed for the calculation of the x, y, and z components of translation of the target isocenter for each repeat CT. In addition to absolute target isocenter translation, the magnitude (sum vector) of isocenter motion and the patient/target rotation about the three principal axes were calculated. RESULTS: Anatomic landmark analysis over a treatment course of 6 weeks revealed a mean target isocenter translation of 0.95 +/- 0.55, 0.58 +/- 0.46, and 0.51 +/- 0.38 mm in x, y, and z directions, respectively. The mean magnitude of isocenter translation was 1.38 +/- 0.48 mm. The 95% confidence interval ([CI], mean translation plus two standard deviations) for repeated isocenter setup accuracy over the 6-week period was 2.34 mm. Average rotations about the x, y, and z axes were 0.41 +/- 0.36, 0.29 +/- 0.25, and 0.18 +/- 0.15 degrees, respectively. Analysis of the accuracy of the first repeated setup control, representative of single-fraction stereotactic radiosurgery situations, resulted in a mean target isocenter translation in the x, y, and z directions of 0.52 +/- 0.38, 0.56 +/- 0.30, and 0.46 +/- 0.25 mm, respectively. The mean magnitude of isocenter translation was 0.99 +/- 0.28 mm. The 95% confidence interval for these radiosurgery situations was 1.55 mm. Average rotations at first repeated setup control about the x, y, and z axes were 0.24 +/- 0.19, 0.19 +/- 0.17, and 0.19 +/- 0.12 degrees, respectively. CONCLUSION: The TALON relocatable head frame was seen to be well suited for immobilization and repositioning of single-fraction stereotactic radiosurgery treatments. Because of its unique removable design, the system was also seen to provide excellent repeat immobilization and alignment for fractionated stereotactic applications. The exceptional accuracy for the single-fraction stereotactic radiosurgical application of the system was seen to deteriorate only slightly over a 6-week fractionated stereotactic treatment course.

Algorithms↗
PubMed2001

Multiple-revolution spiral osteotomy for cranial reconstruction. Technical note.

Various combinations of cranial remodeling techniques are used in an attempt to provide optimal cosmetic results and to reduce possible sequelae associated with craniosynostosis. One element of deformity that is difficult to correct directly is an overly flattened area such as that found in the parietal area in sagittal synostosis, unilaterally in lambdoid synostosis, or even in severe positional molding. The authors present a novel application for recontouring cranial bone, namely the multiple-revolution spiral osteotomy. The advantages of this technique include the avoidance of large areas of craniectomy and immediate correction of the cranial deformity. The surgical procedure, illustrative cases, early results, and apparent benefits of this technique are discussed.

Craniosynostoses↗
PubMed2001

Fulminant radiation-induced necrosis after stereotactic radiation therapy to the posterior fossa. Case report and review of the literature.

The problem of radiation-induced necrosis of normal brain surrounding the target area has been a major catalyst for the development of stereotactically focused radiation therapy. According to current opinion, the effects of stereotactic irradiation are confined to the region targeted. The authors present a case in which the administration of a conventional dose of stereotactically focused irradiation for treatment of a pilocytic astrocytoma produced fulminant necrosis that necessitated a combination of intensive surgical and medical management, after which the patient improved over the course of 1 year. Concomitant with his improvement, the initially remarkable findings on magnetic resonance imaging gradually resolved. In this presentation the authors emphasize the need to evaluate alternatives carefully before a decision is made to administer therapeutic irradiation. Furthermore, they explore the roles that target, host, and dosage factors play in hypersensitivity to radiation injury, the detection of these factors before treatment, and the administration of radioprotective agents. With the growing use of stereotactically focused irradiation as a primary treatment modality for a variety of neurosurgical conditions, it is important to be cognizant of its uncommon but potentially lethal side effects. A cooperative multicenter database in which the outcomes and morbidity following stereotactic irradiation are recorded is essential to the detection of relatively uncommon but severe complications such as those observed in this case.

Adult↗
PubMed2000

Transthoracic approaches to thoracic disc herniations.

The transthoracic approach to herniated thoracic discs is an important procedure in the management of these uncommonly encountered lesions. Whereas posterior and posterolateral microsurgical approaches and thoracoscopic procedures have been widely advocated in the recent neurosurgical literature, the transthoracic operation continues to offer significant advantages in appropriately selected cases. The authors discuss the preoperative considerations, relevant anatomical structures, and surgical technique.

Calcinosis↗
PubMed1999

An unusual case of the complete Currarino triad: case report, discussion of the literature and the embryogenic implications.

OBJECTIVE AND IMPORTANCE: We present and illustrate an unusual case of the complete familial Currarino triad (an association between a bony sacral defect, a presacral mass, and an anorectal malformation) in which the teratoma arose from the conus medullaris and contained mature neurons, glia, and branching ependymal canals that were in communication with a terminal syrinx. The embryogenic implications are discussed. CLINICAL PRESENTATION: The patient was a term neonate when discovered to have imperforate anus. Further workup revealed lumbosacral dysraphism with a presacral mass, a rectovaginal fistula, and a single pelvic kidney. The family pedigree revealed a familial transmission pattern; the patient had a second cousin with anal atresia and a first cousin with similar sacral anomalies. The motor level was L4 with trace L5, and there was absent sensation in the sacral dermatomes. INTERVENTION: A diverting colostomy was performed on Day 14, and the infant returned at 3 months of age to undergo near-total resection through the previous abdominal approach. Only a subtotal resection was possible because the mass arose from the low-lying conus and was firmly adherent to the sacral nerve roots and iliac vessel. Follow-up magnetic resonance imaging performed 18 months after surgery revealed that the residual tumor had not progressed. CONCLUSION: Complete Currarino triad is rare and is familial in half of the cases. The special features of the tumor in our case were the presence of mature neurons with ependymal canals and its origin from the conus. The possible embryogenesis may provide evidence that the caudal notochord is important for organized secondary neurulation.

Abnormalities, Multiple↗
PubMed1997

Thoracolumbar spinal anatomy.

Management of disorders affecting the thoracolumbar spine is predicated on a thorough study of normal anatomy combined with a complete understanding of the ways in which forces act on these anatomic structures (i.e., spinal biomechanics). In this article, the authors review the anatomy of the thoracolumbar spine relevant to the management of disorders affecting the region. This discussion of anatomy is not intended to be exhaustive or definitive but rather to serve as an introductory discussion to consideration of surgical approaches and issues of patient management.

Arteries↗
PubMed1997

Classification and acute management of thoracolumbar fractures.

Successful management of traumatic injuries of the thoracolumbar spine requires understanding of the concepts of spinal stability and instability. There are numerous classifications of injury patterns based on fracture type and the probable forces involved. This article focuses on Denis's three-column theory of spinal stability and its utility in categorizing five injury patterns and the forces involved: specifically, wedge compression fractures, burst fractures, flexion distraction injuries, fracture dislocations, and miscellaneous injuries. The authors also highlight the acute management and evaluation of patients suspected to have these types of injuries.

Acute Disease↗
PubMed1996

Biomechanical analysis of thoracolumbar interbody constructs. How important is the endplate?

STUDY DESIGN: A biomechanical study of human cadaveric thoracic vertebral bodies was conducted using several anterior fusion options subjected to axial loads. This study emphasized the contribution of the endplate to resistance of graft subsidence. OBJECTIVES: To determine the importance of the vertebral endplate in resisting subsidence of various constructs into the vertebral body; the relative efficacy of potential alternative graft constructs such as iliac crest, ribs, humerus, and titanium mesh cage; and the importance of bone mineral content, vertebral level, and cross-sectional graft area on construct subsidence. SUMMARY OF BACKGROUND DATA: As the fixation length of anterior and posterior spinal constructs is reduced, load sharing of the anterior column has become more important to reduce failure of the shorter devices. Several alternative graft constructs and surgical techniques have been used for reconstruction of the anterior column. There exist little comparative data as to whether any of these constructs are superior and whether the vertebral endplate contributes significantly to the integrity of the construct. METHODS: Sixty-three isolated human cadaveric vertebral bodies from T3 to T12 were used to test seven different constructs in direct axial load onto prepared endplates with an electrohydraulic testing device. These constructs were: 1) titanium mesh cage (17 x 22 mm) on intact endplate, 2) C-shaped humerus on intact endplate, 3) tricorticated iliac graft in "tee configuration" on intact endplate, 4) tricorticated iliac graft in cancellous trough, 5) triple rib strut graft, 6) single rib on endplate, and 7) single rib on cancellous body. Dual X-ray absorptiometry assessment of bone mineral content was performed. A uniaxial load was applied with force and displacement data collected to determine maximal load to "failure" of the vertebral body. RESULTS: Preservation of vertebral endplate did not significantly increase the resistance to graft subsidence. The titanium cage construct provided the greatest resistance to axial load. CONCLUSIONS: Preservation of the vertebral endplate may not offer a significant biomechanical advantage in reconstructing the anterior column. Several alternative constructs are mechanically equivalent.

Adult↗
PubMed1996

Intraoperative transligamentous ultrasound in the evaluation of thoracic intraspinal disease. Technique.

STUDY DESIGN: Intraoperative transligamentous ultrasonography was used in a variety of different thoracic surgical procedures for spinal cord compression secondary to neoplastic disease. OBJECTIVES: The utility and practicality of intraoperative transligamentous ultrasonography for thoracic intraspinal disease was evaluated. SUMMARY OF BACKGROUND DATA: Because intraoperative localization and evaluation of targeted levels in the thoracic spine using radiographs is often difficult or imprecise, alternative or complementary techniques may be helpful. Intraoperative transligamentous ultrasound, performed before laminectomy, via an interlaminar window, has not been widely used for thoracic intraspinal pathology. METHODS: A standard 7.5-MHz hand-held probe, used in conjunction with a Codman OR 330 ultrasound machine, was used to evaluate the practicality of intraoperative transligamentous ultrasound in the thoracic spine. RESULTS: A clear sonographic window, permitting visualization of the spine and the intraspinal contents, can frequently be found. However, densely calcified ligamentum flavum or overlapping laminas do not allow effective insonation. Four illustrative cases are presented. CONCLUSIONS: Transligamentous ultrasound before laminectomy can be used for localization and evaluation of intraspinal disease in many patients. Overlapping laminas or calcified ligamentum flavum can impede adequate sonographic visualization, but in these cases adequate intraoperative transligamentous ultrasound evaluation is usually possible through a small laminotomy. Evaluation of intraspinal lesions and localization of the correct surgical level is facilitated by dynamic real time sonographic imaging.

Adult↗
PubMed1995

MR imaging of myxopapillary ependymoma: findings and value to determine extent of tumor and its relation to intraspinal structures.

OBJECTIVE: Myxopapillary ependymomas are highly vascular tumors that arise almost exclusively in the thoracolumbar region and produce symptoms that may mimic discogenic pathology. The purpose of our study was to define the typical MR features of myxopapillary ependymoma and to determine the value of MR imaging in identifying the tumor, establishing its extent, and defining its relationship to intraspinal structures. MATERIALS AND METHODS: MR studies performed on 20 patients (13 men and seven women; mean age, 35 years) with 24 pathologically proven myxopapillary ependymomas were evaluated retrospectively for size and location of lesions, expansion of the central spinal canal and neural foramina, and MR signal characteristics and enhancement patterns. T1-weighted (16 patients), proton density-weighted (15 patients), T2-weighted (14 patients), and enhanced T1-weighted (nine patients) sequences were examined. RESULTS: In all patients, masses were detected on MR images. MR imaging defined solitary masses in 17 patients and multiple lesions in three. Of the 24 tumors, MR imaging characterized 21 as predominately intradural extramedullary, two as intramedullary and intradural extramedullary, and one as extradural postsacral. Two lesions had associated syrinxes. Lesions occurred most often at the level of the L2 vertebral body, and no tumor extended above T9. Tumors spanned an average of four vertebral segments. MR imaging showed expansion of the spinal canal in five of eight tumors that extended over five or more vertebral segments. Two tumors extended into the neural foramina. The T1-weighted signal of the tumor was isointense in 12 patients, hypointense in three patients, and hyperintense in one patient. The T2-weighted signal was always hyperintense. All tumors imaged after administration of IV contrast material showed enhancement. CONCLUSION: MR imaging was valuable in identifying the extent of tumors and in defining their relationship to the intraspinal structures. Although the MR findings in myxopapillary ependymoma are nonspecific, the diagnosis can be suggested by a large, intensely enhancing, intradural extramedullary thoracolumbar mass that extends for several vertebral levels. Imaging protocols should examine the entire thoracolumbar region and include IV contrast.

Adolescent↗
PubMed1993

Hearing improvement after conservative approach for large posterior fossa meningioma.

Hearing preservation during the posterior fossa surgery depends on many factors, including tumor size and site of origin. In many cases, regardless of the presumed tumor origin, the severity of the pure-tone loss or decline in speech discrimination on preoperative testing prompts the surgeon to choose a surgical approach (translabyrinthine or transcochlear) that negates the chance for postoperative functional hearing in the involved ear. We describe a 41-year-old woman with unilateral severe sensorineural hearing loss who experienced a remarkable recovery of hearing after combined retrolabyrinthine and retrosigmoid removal of a 4 cm petrous ridge meningioma using intraoperative cochlear monitoring. Despite the tumor size, early intraoperative loss of wave I and proximity of the tumor to the porus, complete tumor removal was accomplished with preservation of the cochleovestibular bundle. Three weeks postoperatively, the patient noted marked subjective improvement and speech audiometry demonstrated an improvement in word recognition, from 0% to 86%. This improvement has remained 1 year postoperatively, with no evidence of persistent tumor on repeat MRI scan. The case report illustrates the possibility of not just hearing preservation but improvement after removal of even large posterior fossa meningiomas that do not directly invade the cochlear nerve itself.

Adult↗
PubMed1992

An in vitro comparative study of conducting vessels and penetrating arterioles after experimental subarachnoid hemorrhage in the rabbit.

The reactivity of rabbit basilar artery and penetrating arteriolar microvessels was studied in vitro using an isometric-tension measurement technique and an isolated perfused arteriole preparation, respectively. Comparisons were made between reactivities of normal vessels and those obtained from animals subjected to experimental subarachnoid hemorrhage (SAH) 3 days prior to examination. Subarachnoid hemorrhage produced significant increases in basilar artery contraction in response to increasing concentrations of serotonin (5-hydroxytryptamine) (10(-9) to 10(-5) M) and prostaglandin F2 alpha (10(-9) to 10(-5) M) when compared to normal arteries. In addition, SAH attenuated the relaxing effect of acetylcholine following serotonin-induced contraction and of adenosine triphosphate after KCl-induced basilar artery contractions. In contrast to the changes observed in large arteries, cerebral microvessels did not demonstrate significant differences in spontaneous tone or in reactivity to a number of vasoactive stimuli including application of calcium, serotonin, and acetylcholine. On the other hand, small but significant changes in arteriolar responsiveness to changes in extraluminal pH and to application of KCl were noted. Findings from this study suggest that intracerebral resistance vessels of the cerebral microcirculation are not greatly affected by the presence of subarachnoid clot, in contrast to the large arteries in the basal subarachnoid space. The small changes that do occur are qualitatively different from those observed for large arteries. These findings are consistent with the observation of significant therapeutic benefit with the use of calcium channel blockers without changes in angiographically visible vasospasm in large vessels. It is likely, therefore, that calcium antagonists may act to decrease total cerebrovascular resistance at the level of the relatively unaffected microcirculation after SAH without changing large vessel diameter.

Acetylcholine↗
PubMed1991

A study of the effectiveness of the iron-chelating agent deferoxamine as vasospasm prophylaxis in a rabbit model of subarachnoid hemorrhage.

The pathogenesis of cerebral vasospasm occurring after subarachnoid hemorrhage (SAH) is unknown. Several lines of experimentation have suggested a free radical mechanism in the etiology of vasospasm. Iron is an important catalyst in the generation of free radicals and lipid peroxides in response to tissue injury. We hypothesize that the elaboration of iron from the subarachnoid clot might result in enhanced generation of free radicals and lipid peroxidation. If so, then treatment with deferoxamine, an iron-chelating compound, might reduce the formation of free radicals and thereby ameliorate vasospasm. This hypothesis was examined in a rabbit model of experimental cerebral vasospasm. New Zealand White rabbits were divided into the following experimental groups: control (normal) animals (n = 7), control animals treated with deferoxamine (n = 3), animals subjected to SAH and killed on Day 2 (n = 7), animals subjected to SAH on Day 2 and treated with deferoxamine (n = 9), animals subjected to SAH killed on Day 3 (n = 7), and animals subjected to SAH on Day 3 and treated with deferoxamine (n = 7). Deferoxamine treatment (50 mg/kg/8 hours) was begun 16 hours before the induction of SAH and continued until the animals were killed by perfusion fixation. The basilar artery caliber was assessed using morphometric techniques. The diameter of the basilar arteries in the control animals was 0.64 +/- 0.02 mm. Deferoxamine treatment alone did not alter the artery diameter.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

The effect of nicardipine on vasospasm in rabbit basilar artery after subarachnoid hemorrhage.

This study was performed to examine the effect of the dihydropyridine calcium antagonist, nicardipine, on vasospasm after experimental subarachnoid hemorrhage (SAH) in the rabbit. The study was carried out in two parts: 1) effect of intravenous nicardipine (n = 45) and 2) effect of intracisternal nicardipine (n = 21). SAH was induced by injecting 5 ml of autologous arterial blood into the cisterna magna. In the intravenous study, there were five groups: 1) SAH without treatment; 2) SAH with vehicle (saline); 3) SAH and intravenous infusion of low-dose nicardipine (0.01 mg/kg/h); 4) SAH and intravenous infusion of high-dose nicardipine (0.15 mg/kg/h); and 5) controls without SAH. The intravenous infusions were started immediately after SAH and continued for 48 hours until death. In the intracisternal study, there were three groups: 1) SAH without treatment; 2) SAH with intracisternal administration of nicardipine (0.37 mg/h); and 3) controls without SAH. Intracisternal infusions were begun 70 hours after SAH and continued for 2 hours until death. After perfusion-fixation, the basilar artery was removed and processed for morphometric analysis. In the intravenous study, vessels from animals subjected to SAH were significantly narrowed when compared with controls, although after high-dose nicardipine vessel caliber was slightly larger than in the other SAH groups. Animals given intracisternal nicardipine showed a nonsignificant reduction of caliber as compared with controls: only 12% decrease in diameter and 22% decrease in luminal area. In the rabbit SAH model, nicardipine had a very modest effect on vasospasm at the doses tested.

Animals↗
PubMed1991

The management of mild and moderate head injuries.

The majority of patients seeking medical care after head trauma have sustained injuries of mild or moderate severity, i.e., GCS scores of 13 to 15 or 9 to 12, respectively. Mortality rates under these circumstances are generally low; however, serious complications must be detected and treated early. The initial evaluation involves determination of level of consciousness and examination for the presence of focal neurologic deficits. Skull radiography has a limited role in the management of mild and moderate head injuries, but consideration must be given to local factors such as the availability of cranial CT. CT scanning is a safe, noninvasive, and generally cost-effective means of assessing patients at risk for developing intracranial complications. The role of MR imaging in evaluating minor head injuries is not yet established. Patients with an altered level of consciousness require hospitalization in essentially all cases. Selected patients with a GCS score of 15 also benefit from overnight hospitalization and observation. After mild and moderate head injury, significant neuropsychologic deficits are frequent, but are generally finite in their duration. Postconcussive symptoms are also generally self-limited. Although objective evidence suggests that structural brain damage results from mild injuries, the relationship between postconcussional symptoms and structural damage is unclear. Persistent postconcussional symptomatology probably arises from a combination of physiogenic and psychogenic causes. It is possible that early patient education and reassurance will reduce the incidence of prolonged postconcussional symptomatology.

Brain Concussion↗
PubMed1990

Treatment of right hemispheric cerebral infarction by hemicraniectomy.

An anecdotal series of nine patients (three men and six women with an average age of 57 years) presented with progressive neurologic deterioration while on medical therapy for large right hemispheric cerebral infarction. Clinical signs of uncal herniation (anisocoria or fixed and dilated pupils, and/or left hemiplegia with right decerebrate posturing) were present in seven of these nine patients. Computerized tomography of the head confirmed mass effect from cerebral edema. It was the clinical judgment of the treating neurologists and neurosurgeons that each of these nine patients would perish unless surgical decompression of the infarcted brain was performed. Accordingly, each was treated with right hemicraniectomy and dural augmentation. Six patients demonstrated neurologic improvement on the first postoperative day. One patient, with a postoperative diagnosis of lung cancer, died 1 month after surgery. The remaining eight patients are currently living with their families with a follow-up period ranging from 5 to 25 months. Patient outcome as evaluated by the Barthel Index indicates that three individuals are functioning with minimal assistance and that the remaining six patients are functionally dependent. After rehabilitative therapy, four patients returned for elective cranioplasty. These results suggest that hemicraniectomy can be an effective lifesaving procedure for malignant cerebral edema after large hemispheric infarction.

Activities of Daily Living↗