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The Nd:YAG laser in neurosurgery

Part 2. Clinical studies: an adjunctive measure for hemostasis in resection of arteriovenous malformations

Robert E. Wharen Jr., Robert E. Anderson, and Thoralf M. Sundt Jr.

✓ The Nd:YAG laser has been used safely to aid in the resection of 10 cases of parenchymal arteriovenous malformations (AVM's). The laser was, found helpful for: 1) defining the plane between the AVM and the brain; 2) coagulating any dural component of the AVM; and 3) achieving hemostasis of the bed following resection of the lesion. However, its overall benefit in the resection of AVM's remains to be determined, as it could not arrest active high-flow bleeding from the thin-walled vessels feeding the deep portion of the AVM. This was attributed to the inherent characteristics of these vessels, since the instrument has been effective in non-AVM arteries of similar dimensions containing contractile elements in the vessel walls. Future refinements in focusing instrumentation and operative technique should enhance its capabilities and usefulness. When used within the recommended power range, the Nd:YAG laser is safe and its penetration predictable. The fiberoptic cable light delivery system allows excellent mobility of the handpiece, but the protective eyewear laser-light filters reduce the available light to the surgeon. The instrument appears promising but more work is required.

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Thrombosed arteriovenous malformations of the brain

An important entity in the differential diagnosis of intractable focal seizure disorders

Robert E. Wharen Jr., Bernd W. Scheithauer, and Edward R. Laws Jr.

✓ Thrombosed arteriovenous malformations (AVM's) in patients with no previous history of hemorrhage are uncommon but benign lesions that present with clinical and radiographic findings which are often indistinguishable from those of other mass lesions, particularly low-grade gliomas. The authors report seven cases of thrombosed AVM's presenting as intractable seizure disorders in which the radiographic studies had suggested a low-grade glioma. All seven patients are now seizure-free 2 to 40 months postoperatively. The importance of surgical exploration in the management of such patients is emphasized. A review of 32 cases reported in the literature is presented. The reasons why angiography may fail to demonstrate an AVM, and the possible etiologies for the spontaneous thrombosis of an AVM are discussed.

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The Nd:YAG laser in neurosurgery

Part 1. Laboratory investigations: dose-related biological response of neural tissue

Robert E. Wharen Jr., Robert E. Anderson, Bernd Scheithauer, and Thoralf M. Sundt Jr.

✓ The biological response of normal cat brain to Nd:YAG laser light was studied both in vitro and in vivo to evaluate the potential safety of this laser for coagulation in brain tissue. Transmission studies revealed a blood:brain absorption ratio of 100:1 indicating the selective absorption of Nd:YAG light by hemoglobin and enabling Nd:YAG light to selectively heat blood vessels compared to brain tissue. In vivo temperature recordings and pathological evaluation demonstrated a remarkable ability of the brain to dissipate the thermal energy produced by Nd:YAG light with only a small amount of structural damage. Powers of 10 W applied for 8 seconds using a 1.2-mm focused probe resulted in a penetration depth in normal brain of only 2 mm. Thermal recordings also revealed that blood is heated to 90% of its maximum temperature within 3 seconds, while the brain temperature increases linearly as the duration of the laser pulse is increased. In addition, the localized heating of brain tissue was cooled rapidly within seconds following cessation of the laser pulse. These findings indicate that by using short, intermittent pulses of light focused upon blood vessels, damage to the surrounding tissue can be minimized, and the Nd:YAG laser can be used safely as an adjunctive measure for hemostasis in many neurosurgical procedures.

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Alois A. Obwegeser, Ryan J. Uitti, John A. Lucas, Robert J. Witte, Margaret F. Turk, and Robert E. Wharen Jr.

Object. The authors studied neuropsychological performance following microelectrode-guided posteroventral pallidotomy in patients with Parkinson's disease (PD) and evaluated correlations with presurgical and surgical factors.

Methods. Neuropsychological changes 3 months (43 patients) and 12 months (27 patients) after microelectrode-guided pallidotomy for PD are reported in a series of 44 consecutive patients with the disease, who improved neurologically, as measured by the Unified Parkinson's Disease Rating Scale (UPDRS) in both the “off” (p < 0.001) and best “on” (p < 0.001) states.

Findings of the vocabulary subtest of the Wechsler Adult Intelligence Scale—Revised (p < 0.01), Letter Fluency (p < 0.001), Verbal Fluency for semantic categories (p < 0.001), and the Wisconsin Card Sorting Test (p < 0.01) showed a significant decline in neuropsychological performance in patients 3 months after undergoing left-sided pallidotomy. Impairment in the language domain (semantic fluency) persisted at the 12-month follow-up examination (p < 0.01). Visual memory improved after right-sided pallidotomies (p < 0.01 after 3 months), with a nonsignificant trend toward persistent improvement 1 year postsurgery (p < 0.02 after 12 months). Preoperative semantic fluency was influenced by patient age (p < 0.001) and by the width of the third ventricle (p < 0.05), as measured by magnetic resonance imaging.

A regression model revealed that semantic fluency 3 months postoperatively was significantly affected by the baseline score (p < 0.001), side of surgery (p < 0.001), handedness (p < 0.01), and patient age (p < 0.05). However, postoperative lesion volume, lesion location, number of tracks, number of lesions, distance from anatomical landmarks, or UPDRS score did not significantly contribute to neuropsychological outcome.

Conclusions. Neuropsychological changes in a cohort of patients with PD who underwent pallidotomy and experienced excellent clinical benefits and minimum postoperative complications, emphasize the importance of neuropsychological examinations and further investigation of predictive factors.

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Jerzy Slowinski, Ryan J. Uitti, John D. Putzke, and Robert E. Wharen Jr.

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Qurat ul Ain Khan, Robert E. Wharen, Sanjeet S. Grewal, Colleen S. Thomas, H. Gordon Deen Jr., Ronald Reimer, Jay A. Van Gerpen, Julia E. Crook, and Neill R. Graff-Radford


Management of idiopathic normal-pressure hydrocephalus (iNPH) is hard because the diagnosis is difficult and shunt surgery has high complication rates. An important complication is overdrainage, which often can be treated with adjustable–shunt valve manipulations but also may result in the need for subdural hematoma evacuation. The authors evaluated shunt surgery overdrainage complications in iNPH and their relationship to lumbar puncture opening pressure (LPOP).


The authors reviewed the charts of 164 consecutive patients with iNPH who underwent shunt surgery at their institution from 2005 to 2011. They noted age, sex, presenting symptoms, symptom duration, hypertension, body mass index (BMI), imaging findings of atrophy, white matter changes, entrapped sulci, LPOP, valve opening pressure (VOP) setting, number of valve adjustments, serious overdrainage (subdural hematoma requiring surgery), radiological overdrainage (subdural hematomas or hygroma seen on postoperative imaging), clinical overdrainage (sustained or postural headache), other complications, and improvements in gait, urine control, and memory.


Eight patients (5%) developed subdural hematomas requiring surgery. All had an LPOP of greater than 160 mm H2O and an LPOP-VOP of greater than 40 mm H2O. Radiological overdrainage was more common in those with an LPOP of greater than 160 mm H2O than in those with an LPOP of less than 160 mm H2O (38% vs 21%, respectively; p = 0.024). The BMI was also significantly higher in those with an LPOP of greater than 160 mm H2O (median 30.2 vs 27.0, respectively; p = 0.005).


Serious overdrainage that caused subdural hematomas and also required surgery after shunting was related to LPOP and LPOP-VOP, which in turn were related to BMI. If this can be replicated, individuals with a high LPOP should have their VOP set close to the LPOP, or even higher. In doing this, perhaps overdrainage complications can be reduced.