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Letter to the Editor

Intraconal lesions

Sébastien Freppel and Thierry Civit

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Transfrontoethmoidal approach to medial intraconal lesions

Laboratory investigation

Pakrit Jittapiromsak, Pushpa Deshmukh, Peter Nakaji, Robert F. Spetzler, and Mark C. Preul

Object

The standard superior craniotomy approach through the orbital roof is obstructed by numerous muscles, nerves, and vessels. Accessing the medial intraconal space also involves considerable brain retraction. The authors present a modified approach through the frontal sinus that overcomes these limitations.

Methods

Seven fixed silicone-injected cadaveric specimens were dissected bilaterally. In addition to the superior orbital wall, the ethmoidal sinuses and medial orbital wall were removed. The anatomical relationships between the major neurovascular complexes in the medial intraconal space and the optic nerve were observed.

Results

Intraconally, working space was created both in a “superior window” between the superior oblique and levator palpebrae muscle and in a “medial window” between the superior oblique and medial rectus muscle. The superior window mainly created an ipsilateral trajectory to the deep target. The medial window, which created a contralateral trajectory, provided a more inferior view of the medial intraconal space. Removal of the medial orbital wall further widened the exposure obtained from the superior window. The combination of these working windows makes the medial surface of the optic nerve available for exploration from multiple angles. Most of the major neurovascular complexes of the posterior orbit can be retracted safely without impinging on the optic nerve.

Conclusions

This novel extradural transfrontoethmoidal approach affords a direct view to the medial posterior orbit without major conflicts with intraconal neurovascular structures and requires minimal brain manipulation. The approach appears to offer advantages for medially located intraconal lesions.

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Quantitative analysis of the working area and angle of attack for the retrosigmoid, combined petrosal, and transcochlear approaches to the petroclival region

Rungsak Siwanuwatn, Pushpa Deshmukh, Eberval Gadelha Figueiredo, Neil R. Crawford, Robert F. Spetzler, and Mark C. Preul

Object

The authors quantitatively assessed the working areas and angles of attack associated with retrosigmoid (RS), combined petrosal (CP), and transcochlear (TC) craniotomies.

Methods

Four silicone-injected cadaveric heads were bilaterally dissected using three approaches progressing from the least to the most extensive. Working areas were determined using the Optotrak 3020 system on the upper and middle thirds of the petroclivus and brainstem. Angles of attack were studied using the Elekta SurgiScope at the Dorello canal and the origin of the anterior inferior cerebellar artery (AICA).

The TC approach provided significantly greater (p < 0.001) working areas at the petroclivus (755.6 ± 130.1 mm2) and brainstem (399.3 ± 68.2 mm2) than the CP (354.1 ± 60.3 and 289.7 ± 69.9 mm2) and RS approaches (292.4 ± 59.9, 177.2 ± 54.2 mm2, respectively). The brainstem working area associated with the CP approach was significantly larger (p < 0.001) than that associated with the RS route. There was no difference in the petroclival working area comparing the CP and RS approaches (p = 0.149). The horizontal and vertical angles of attack achieved using the TC approach were wider than those of the CP and RS at the Dorello canal and the origin of the AICA (p < 0.001).

Conclusions

The CP approach offers a more extensive working area than the RS for lesions involving the anterolateral surface of the brainstem, but not for petroclival lesions. The TC approach provides the widest corridor, improving the working area and angle of attack to both areas, but hearing must be sacrificed and the facial nerve is at risk.

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Autonomic and histopathological effects of percutaneous trigeminal ganglion compression in the rabbit

Mark C. Preul, Phillip B. Long, Jeffrey A. Brown, Manuel E. Velasco, and Michael T. Weaver

✓ The histopathological and autonomic effects of percutaneous trigeminal ganglion compression for trigeminal neuralgia were studied in New Zealand White rabbits. Drops in mean arterial blood pressure of 38% and in heart rate of 30% were observed during compression (p < 0.0001). Corneal reflex, pinprick sensation, and mastication strength were intact in 13 of 14 rabbits after compression. These findings resembled the effects of percutaneous compression in humans and suggested that the New Zealand White rabbit is a useful model for the study of percutaneous compression.

Trigeminal sensory roots and ganglia from 14 rabbits killed at intervals from 1 to 84 days after percutaneous compression were sectioned and stained using immunoperoxidase for neurofilaments, hematoxylin and eosin, luxol fast blue, and cresyl echt violet. Focal axonal damage and demyelination were present 7 days after compression. No difference could be detected in the perikaryonal distribution of neurofilaments between compressed and control trigeminal ganglia. Focal demyelination and Schwann cell proliferation preceding remyelination were present in the trigeminal sensory root at 84 days. Differential injury of axons compared to trigeminal ganglion cell bodies suggests that axonal regeneration is possible and may contribute to the recovery of motor and sensory function in patients after percutaneous compression.

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No woman alone: Dorothy Russell’s legacy to neurosurgery

Jubran H. Jubran, Lena Mary Houlihan, Ann J. Staudinger Knoll, Dara S. Farhadi, Richard Leblanc, and Mark C. Preul

Dorothy Russell’s contributions to neuropathology are pivotal in the evolution of modern neurosurgery. In an era preferential to men in medicine, she entered the second medical school class to include women at the London Hospital Medical College in 1919. In the laboratory of Hubert Turnbull, she met Hugh Cairns, who would become her professional neurosurgeon-neuropathologist partner. In 1929, arriving at McGill’s Royal Victoria Hospital in Montreal, where Wilder Penfield and William Cone had just begun a neurosurgical service, Russell elucidated the origin and activity of microglia. Returning to London, Russell continued to work closely with Cairns for many years. Along with J. O. W. Bland, she became the first to culture gliomas and meningiomas. Her work on the effects of and fatality rates associated with head injuries among soldiers during World War II led to the initiation of helmet requirements for motorcyclists. Her textbook, Pathology of the Tumours of the Nervous System, written with Lucien Rubinstein, is considered a landmark text in neurosurgery, neuropathology, and neurooncology. Honored by Penfield and Cone as their first neurosurgery research fellow, Russell was considered a favorite of the Montreal Neurological Institute. Dorothy Russell’s extraordinary career elucidating the mysteries of neurosurgical pathology has made an enduring mark on neurosurgery.

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Letter to the Editor. Transorbital puncture of the ventricular system

Nelson A. Picard and Carlos A. Zanardi

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Retromastoid-transmuscular identification and harvest of the occipital artery during retrosigmoid craniotomy

Ali Tayebi Meybodi, Michael T. Lawton, Leandro Borba Moreira, Xiaochun Zhao, Michael J. Lang, Peter Nakaji, and Mark C. Preul

OBJECTIVE

Harvesting the occipital artery (OA) is challenging. The subcutaneous OA is usually found near the superior nuchal line and followed proximally, requiring a large incision and risking damage to the superficially located OA. The authors assessed the anatomical feasibility and safety of exposing the OA through a retromastoid-transmuscular approach.

METHODS

Using 10 cadaveric heads, 20 OAs were harvested though a 5-cm retroauricular incision placed 5 cm posterior to the external auditory meatus. The underlying muscle layers were sequentially cut and recorded before exposing the OA. Changes in the orientation of muscle fibers were used as a roadmap to expose the OA without damaging it.

RESULTS

The suboccipital segment of the OA was exposed without damage after incising two consecutive layers of muscles and their investing fasciae. These muscles displayed different fiber directions: the superficially located sternocleidomastoid muscle with vertically oriented fibers, and the underlying splenius capitis with anteroposteriorly (and mediolaterally) oriented fibers. The OA could be harvested along the entire length of the skin incision in all specimens. If needed, the incision can be extended proximally and/or distally to follow the OA and harvest greater lengths.

CONCLUSIONS

This transmuscular technique for identification of the OA is a reliable method and may facilitate exposure and protection of the OA during a retrosigmoid approach. This technique may obviate the need for larger incisions when planning a bypass to nearby arteries in the posterior circulation via a retrosigmoid craniotomy. Additionally, the small skin incision can be enlarged when a different craniotomy and/or bypass is planned or when a greater length of the OA is needed to be harvested.

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Anatomical assessment of the endoscopic endonasal approach for the treatment of paraclinoid aneurysms

Ali Tayebi Meybodi, Leandro Borba Moreira, Andrew S. Little, Michael T. Lawton, and Mark C. Preul

OBJECTIVE

Endoscopic endonasal approaches (EEAs) are increasingly being incorporated into the neurosurgeon’s armamentarium for treatment of various pathologies, including paraclinoid aneurysms. However, few anatomical assessments have been performed on the use of EEA for this purpose. The aim of the present study was to provide a comprehensive anatomical assessment of the EEA for the treatment of paraclinoid aneurysms.

METHODS

Five cadaveric heads underwent an endonasal transplanum-transtuberculum approach to expose the paraclinoid area. The feasibility of obtaining proximal and distal internal carotid artery (ICA) control as well as the topographic location of the origin of the ophthalmic artery (OphA) relative to dural landmarks were assessed. Limitations of the EEA in exposing the supraclinoid ICA were also recorded to identify favorable paraclinoid ICA aneurysm projections for EEA.

RESULTS

The extracavernous paraclival and clinoidal ICAs were favorable segments for establishing proximal control. Clipping the extracavernous ICA risked injury to the trigeminal and abducens nerves, whereas clipping the clinoidal segment put the oculomotor nerve at risk. The OphA origin was found within 4 mm of the medial opticocarotid point on a line connecting the midtubercular recess point to the medial vertex of the lateral opticocarotid recess. An average 7.2-mm length of the supraclinoid ICA could be safely clipped for distal control. Assessments showed that small superiorly or medially projecting aneurysms were favorable candidates for clipping via EEA.

CONCLUSIONS

When used for paraclinoid aneurysms, the EEA carries certain risks to adjacent neurovascular structures during proximal control, dural opening, and distal control. While some authors have promoted this approach as feasible, this work demonstrates that it has significant limitations and may only be appropriate in highly selected cases that are not amenable to coiling or clipping. Further clinical experience with this approach helps to delineate its risks and benefits.

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From Krönlein, through madness, to a useful modern surgery: the journey of the transorbital corridor to enter the neurosurgical armamentarium

Lena Mary Houlihan, Evgenii Belykh, Xiaochun Zhao, Michael G. J. O’Sullivan, and Mark C. Preul

Transorbital surgery has gained recent notoriety because of its incorporation into endoscopic skull base surgery. The use of this surgical corridor has been pervasive throughout the 20th century. It has been utilized by multiple disciplines for both clinical and experimental purposes, although its historical origin is medically and ethically controversial. Hermann Knapp first introduced the orbital surgical technique in 1874, and Rudolf Krönlein introduced his procedure in 1889. Rivalry between Walter Dandy in neurosurgery and Raynold Berke in ophthalmology further influenced methods of tackling intracranial and intraorbital pathologies. In 1946, Walter Freeman revolutionized psychosurgery by completing seemingly successful transorbital leucotomies and promoting their minimally invasive and benign surgical characteristics. However, as Freeman’s legacy came into disrepute, so did the transorbital brain access corridor, again resulting in its stunted evolution. Microsurgery and endoscopy further influenced the use, or lack thereof, of the transorbital corridor in neurosurgical approaches. Historical analysis of present goals in modern skull base surgery echoes the principles established through an approach described almost 150 years ago: minimal invasion, minimal morbidity, and priority of patient satisfaction. The progression of the transorbital approach not only reflects psychosocial influences on medical therapy, as well as the competition of surgical pioneers for supremacy, but also describes the diversification of skull base techniques, the impact of microsurgical mastery on circumferential neurosurgical corridors, the influence of technology on modernizing skull base surgery, and the advancing trend of multidisciplinary surgical excellence.

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Microsurgical anatomy of safe entry zones to the brainstem

Daniel D. Cavalcanti, Mark C. Preul, M. Yashar S. Kalani, and Robert F. Spetzler

OBJECT

The aim of this study was to enhance the planning and use of microsurgical resection techniques for intrinsic brainstem lesions by better defining anatomical safe entry zones.

METHODS

Five cadaveric heads were dissected using 10 surgical approaches per head. Stepwise dissections focused on the actual areas of brainstem surface that were exposed through each approach and an analysis of the structures found, as well as which safe entry zones were accessible via each of the 10 surgical windows.

RESULTS

Thirteen safe entry zones have been reported and validated for approaching lesions in the brainstem, including the anterior mesencephalic zone, lateral mesencephalic sulcus, intercollicular region, peritrigeminal zone, supratrigeminal zone, lateral pontine zone, supracollicularzone, infracollicularzone, median sulcus of the fourth ventricle, anterolateral and posterior median sulci of the medulla, olivary zone, and lateral medullary zone. A discussion of the approaches, anatomy, and limitations of these entry zones is included.

CONCLUSIONS

A detailed understanding of the anatomy, area of exposure, and safe entry zones for each major approach allows for improved surgical planning and dissemination of the techniques required to successfully resect intrinsic brainstem lesions.