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Paul H. Chapman, Eric Cosman and Michael Arnold

✓ After surgery for posterior fossa or third ventricular tumors, hydrocephalus may persist or evolve. Proper management of this complication requires timely detection. Temporary external ventricular drainage has been suggested by some authors as an adjunct to clinical observations and radiographic studies for unshunted patients. As an alternative, the authors have used a telemetric method of pressure monitoring in association with a ventricular catheter and subcutaneous reservoir. This has been found useful in eight patients without the disadvantages inherent in other methods of management.

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Peter McL. Black and Paul H. Chapman

✓ In two cases of normal pressure hydrocephalus, the patients suffered transient abducens weakness following a shunting procedure.

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Subtorcular occipital encephaloceles

Anatomical considerations relevant to operative management

Paul H. Chapman, Brooke Swearingen and Verne S. Caviness

✓ Three cases of occipital encephalocele, one with associated myelomeningocele, are presented. All received preoperative evaluation with magnetic resonance imaging. Such studies provide optimal demonstration of the cerebral and hindbrain anatomy to guide operative treatment and formulate prognosis. Review of available radiographic, operative, and pathological information suggests that most, if not all, occipital encephaloceles are associated with an anomaly of the hindbrain, and the usual anomaly is a rhombic roof encephalocele. In such cases, the site of cranial herniation is caudal to the torcula, regardless of the presence or absence of occipital lobe tissue within the sac. Experimental and clinical analysis suggests that occipital encephaloceles most likely arise from abnormalities in the development of the skull base.

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Paul H. Chapman and David M. Frim

✓ The authors report the cases of three children in whom symptomatic syringomyelia occurredde novo following an operation to relieve retethering of a previously treated lipomyelomeningocele. No patient had a Chiari malformation. In two cases, magnetic resonance imaging performed before the first operation did not show a syrinx. At the time of surgery to relieve retethering, it was discovered that one of these patients had a minor degree of terminal hydromyelia and the other had a prominent central canal within the conus medullaris. The third patient was initially studied by means of myelography, which gave no indication of a syrinx, and one was not found at the time of the surgery to release the retethering. Neurological deficits appeared abruptly within several months of operation in two children, and insidiously after 12 to 18 months in the other symptomatic individual. In all three cases, the syrinx involved the distal spinal cord adjacent to the site of the lipoma. Treatment consisted of syringosubarachnoid shunting, which arrested the progression of deficits but only partially reversed them. The details of each case are presented and the possible mechanism of syrinx formation discussed. Early recognition and treatment of this unusual but important problem are emphasized.

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Paul H. Chapman, Hugh D. Curtin and Michael J. Cunningham

✓ The authors describe an unusual meningocele of the lateral wall of the cavernous sinus and the anterior skull base in a young patient with typical stigmata of neurofibromatosis Type 1 (NF1). This lesion was discovered during evaluation for recurrent meningitis. It represented an anterior continuation of Meckel's cave into a large cerebrospinal fluid space within the lateral wall of the cavernous sinus, extending extracranially through an enlarged superior orbital fissure into the pterygopalatine fossa adjacent to the nasal cavity. It was successfully obliterated, via an intradural middle fossa approach, with fat packing and fenestration into the subarachnoid space. This meningocele most likely represents a variant of cranial nerve dural ectasia occasionally seen in individuals with NF1. It has as its basis the same mesodermal defect responsible for the more common sphenoid wing dysplasia and spinal dural ectasias identified with this condition. Involvement of the trigeminal nerve with expansion of the lateral wall of cavernous sinus has not been reported previously. The authors surmise, however, that it may be present in some cases of orbital meningocele associated with sphenoid wing dysplasia.

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Clark C. Chen, Paul Chapman, Joshua Petit and Jay Loeffler

Object

Photon energy deposition from gamma or photon sources follows the law of exponential decay. Consequently, energy is deposited over the entire path of the radiation beam, resulting in dose distribution before and after the target is reached. In contrast, the physical properties of protons are such that energy deposition occurs with no exit dose beyond the target volume. Therefore, relative to photons, proton beams represent a superior platform for the administration of radiosurgery.

Methods

In this review, the authors will discuss the fundamental principles underlying photon- and proton-based stereotactic radiosurgery (SRS). The clinical efficacy of proton-based SRS in the treatment of arteriovenous malformations, vestibular schwannomas, and pituitary adenomas is reviewed.

Results

Direct comparisons of clinical results attained using photon- and proton-based SRS are confounded by a bias toward reserving proton beams for the treatment of larger and more complex lesions. Despite this bias, the clinical outcomes for proton-based SRS have been excellent and have been at least comparable to those for photon-based treatments.

Conclusions

The physical properties of proton radiation offer superior conformality in dose distribution relative to photon irradiation. This advantage becomes more apparent as the lesion size increases and will probably be magnified with the development of intensity-modulated proton techniques.

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Jens R. Chapman, Paul A. Anderson, Christopher Pepin, Sean Toomey, David W. Newell and M. Sean Grady

✓ Fractures, tumors, and other causes of instability at the cervicothoracic junction pose diagnostic and treatment challenges. The authors report on 23 patients with instability of the cervicothoracic region, which was treated with posterior plate fixation and fusion between the lower cervical and upper thoracic spine. During operation AO reconstruction plates with 8- or 12-mm hole spacing were affixed to the spine using screws in the cervical lateral masses and the thoracic pedicles. Postoperative immobilization consisted of the patient's wearing a simple external brace for 2 months. The following parameters were analyzed during the pre- and postoperative treatment period: neurological status, spine anatomy and reconstruction, and complications. Follow up consisted of clinical and radiographic examinations (mean duration of follow up, 15.4 months; range, 6–41 months).

No neurovascular or pulmonary complications arose from surgery. All patients achieved a solid arthrodesis based on flexion-extension radiographs. There was no significant change in angulation during the postoperative period, but one patient had an increase in translation that was not clinically significant. There were no hardware complications that required reoperation. One patient requested hardware removal in hopes of reducing postoperative pain in the cervicothoracic region. One postoperative wound infection required debridement but not hardware removal. The authors conclude that posterior plate fixation is a satisfactory method of treatment of cervicothoracic instability.

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Christopher S. Ogilvy, Paul H. Chapman, Mark Gray and Suzzane M. de la Monte

✓ Meningioangiomatosis is a rare benign tumor of the central nervous system. Most cases are associated with von Recklinghausen' neurofibromatosis. The case of a 9-year-old boy with a 6-year history of temporal lobe epilepsy is reported. Computerized tomography revealed a hyperdense lesion in the region. The lesion was avascular on angiography. Magnetic resonance imaging showed a large well-demarcated abnormality with hyper- and hypodense regions on T2-weighted images. The abnormality did not extend into the white matter. Histological sections of the biopsy specimen disclosed an organoid transcortical lesion composed of interlacing finger-like fascicles of vascularized fibromeninges. Most fascicles exhibited one or more central slit-like capillaries cuffed by fibroblasts and invaginated meningeal tissue arranged in a parallel or concentric manner. Typical psammoma bodies were evident throughout the lesion, as well as in the intervening, mildly gliotic cerebral cortex. Proliferative meningothelial cells were present in the overlying leptomeninges. The lesion in this case was a hamartoma rather than a neoplasm.

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L. Dade Lunsford

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John S. Yu, M. Priscilla Short, James Schumacher, Paul H. Chapman and Griffith R. Harsh IV

✓ The authors describe two cases of intramedullary hemorrhage caused by thoracic hemangioblastoma. Both patients presented with acute paraplegia. The lesion in the first case was diagnosed by myelography and in the second by magnetic resonance imaging. Emergency surgical evacuation of the intramedullary hematoma and tumor was performed in these patients. Hemangioblastoma was confirmed by histopathological examination in both cases. Both patients remain paraplegic after 7 and 1 years, respectively. Intramedullary hemorrhage is a rare and devastating effect of spinal hemangioblastoma.