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Melissa M. Stamates and Ricky H. Wong

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Serdar Ercan, Alba Scerrati, Phengfei Wu, Jun Zhang and Mario Ammirati

OBJECTIVE

The subtemporal approach is one of the surgical routes used to reach the interpeduncular fossa. Keyhole subtemporal approaches and zygomatic arch osteotomy have been proposed in an effort to decrease the amount of temporal lobe retraction. However, the effects of these modified subtemporal approaches on temporal lobe retraction have never been objectively validated.

METHODS

A keyhole and a classic subtemporal craniotomy were executed in 4 fresh-frozen silicone-injected cadaver heads. The target was defined as the area bordered by the superior cerebellar artery, the anterior clinoid process, supraclinoid internal carotid artery, and the posterior cerebral artery. Once the target was fully visualized, the authors evaluated the amount of temporal lobe retraction by measuring the distance between the base of the middle fossa and the temporal lobe. In addition, the volume of the surgical and anatomical corridors was assessed as well as the surgical maneuverability using navigation and 3D moldings. The same evaluation was conducted after a zygomatic osteotomy was added to the two approaches.

RESULTS

Temporal lobe retraction was the same in the two approaches evaluated while the surgical corridor and the maneuverability were all greater in the classic subtemporal approach.

CONCLUSIONS

The zygomatic arch osteotomy facilitates the maneuverability and the surgical volume in both approaches, but the temporal lobe retraction benefit is confined to the lateral part of the middle fossa skull base and does not result in the retraction necessary to expose the selected target.

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Varun R. Kshettry, Joung H. Lee and Mario Ammirati

Interest in studying the anatomy of the abducent nerve arose from early clinical experience with abducent palsy seen in middle ear infection. Primo Dorello, an Italian anatomist working in Rome in the early 1900s, studied the anatomy of the petroclival region to formulate his own explanation of this pathological entity. His work led to his being credited with the discovery of the canal that bears his name, although this structure had been described 50 years previously by Wenzel Leopold Gruber. Renewed interest in the anatomy of this region arose due to advances in surgical approaches to tumors of the petroclival region and the need to explain the abducent palsies seen in trauma, intracranial hypotension, and aneurysms. The advent of the surgical microscope has allowed more detailed anatomical studies, and numerous articles have been published in the last 2 decades. The current article highlights the historical development of the study of the Dorello canal. A review of the anatomical studies of this structure is provided, followed by a brief overview of clinical considerations.

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Editorial

Contralateral approach to the atrium of the lateral ventricle

Roberto C. Heros

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Letter to the Editor

Transfalcine approach

Atul Goel

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Song Wang, Asem Salma and Mario Ammirati

Object

The posterior interhemispheric transprecuneus gyrus approach is one of the surgical routes that has been suggested to reach the atrium of the lateral ventricle. It has the advantage of avoiding the disruption of the optic radiations; however, it has a narrow working area that at times makes the execution of this approach rather challenging. The aim of this study was to test a modification of the approach that might create a better surgical angle and a wider corridor by accessing the atrium from the contralateral side after transection of the falx. The authors named this new approach the “posterior interhemispheric transfalx transprecuneus approach.”

Methods

The posterior interhemispheic transfalx transprecuneus approach was performed bilaterally on 6 fresh adult cadaveric specimens for a total of 12 procedures. Every head was held in the semisitting position and a parasagittal parietooccipital craniotomy on the contralateral side of the targeted ventricle was executed. The dura mater was opened and reflected based on the sagittal sinus. Then the falx was cut in a triangular fashion based on the inferior sagittal sinus. Using the parietooccipital artery and sulcus as landmarks, the contralateral precuneus gyrus was indentified, and a small area of the gyrus was transected to gain access to the atrium. A neuronavigational system was also used to conduct this approach. The working angle of this approach and other distances were measured

Results

The authors were able to visualize the ventricular atrium, posterior part of the temporal horn, pulvinar, and choroid plexus in all specimens. The temporal horn could be exposed for a length of 20–30 mm from the atrium. The working angle of the approach was better than that of the classic posterior interhemispheric transprecuneus approach with a mean value of 44.5° as opposed to 25.8°. The distance from the middle point of the corticotomy to the splenium ranged from 11 to 16 mm (mean 13.3 mm); the distance to the torcula, from 34 to 53 mm (mean 41.3 mm); and the distance to the atrium, from 22 to 31 mm (mean 25.7 mm).

Conclusions

Results of this study suggested that the proposed approach can expose the atrium and the posterior part of the temporal horn of the lateral ventricle with a wider surgical angle compared with the conventional homolateral posterior interhemispheric transprecuneus gyrus approach. Moreover, by minimizing the amount of brain retraction homolateral to the target, this approach could make navigation more accurate.

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Promod Pillai, Abhik Ray-Chaudhury, Mario Ammirati and E. Antonio Chiocca

✓ Sarcoidosis is a multisystemic granulomatous disease characterized by noncaseating epithelioid granulomata that affects the lung in over 90% of patients and the central nervous system (CNS) in 5–9%. Neurosarcoidosis often occurs as multifocal meningeal and parenchymal lesions, and its diagnosis is particularly difficult in the absence of concomitant systemic disease. Hypothalamic-pituitary sarcoidosis occurs in fewer than 10% of patients with neurosarcoidosis and has been previously reported in association with profound endocrinological dysfunction. The authors report the case of a patient with isolated pituitary sarcoidosis who was first evaluated for visual symptoms and showed no preoperative endocrinological dysfunction or evidence of multisystemic or other CNS involvement. To the authors' knowledge, only 1 other such presentation is previously reported in the English literature. Such presentations are diagnostically and therapeutically challenging, and definitive diagnosis requires obtaining a biopsy specimen of the lesion with histological proof of noncaseating epithelioid granuloma, as well as the exclusion of other possible entities.

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Mario Ammirati, Mariel Delgado, H. Wayne Slone and Abhik Ray-Chaudhury

✓ Dermoid cysts are rare, benign, congenital tumors. Most case series thus far have featured intradural tumors. The authors report on a case of an extradural dermoid tumor of the middle cranial fossa with osseous invasion, successfully removed using a left subtemporal extradural approach. The clinical presentation, histological features, radiological findings, and management of this unique case are described.

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Mario Ammirati and Antonio Bernardo

Object

The superior orbital fissure (SOF) is an important landmark in the neurosurgical pterional approach, but the anatomical features of the SOF and the procedures necessary to fully expose it and its contents have not been detailed. Although the pterional approach is commonly used during skull base or vascular surgery by neurosurgeons who may already be familiar with its nuances and anatomical relationships to the SOF, this knowledge may also be useful to the wider neurosurgical community. The authors describe the spatial relationships of the contents of the SOF and suggest a specific sequence of steps for exposing the SOF region in a pterional approach.

Methods

Using standard microsurgical equipment and instruments, the authors performed 20 pterional approaches in 10 embalmed cadaver heads in which the vascular systems had been injected with colored material.

Five sequential steps were delineated for approaching and dissecting the SOF and its contents: 1) drilling the sphenoidal ridge, anterior clinoidal process, and part of the greater and lesser wings of the sphenoid; 2) resecting the dural bridge; 3) detaching the hemispheric dura mater, thereby exposing the anterior portion of the cavernous sinus and the neural component entering the SOF; 4) identifying and dissecting the extraanular structures; and 5) opening the anulus of Zinn and identifying its neural constituents.

Conclusions

Knowing the 3D relationships of the contents of the SOF encountered in the pterional approach enables safe neurosurgical access to the area. The proposed sequence of steps allows a controlled exposure of the SOF and surrounding areas. Untethering the frontotemporal lobe by transecting the dural bridge connecting the dura to the perior-bita allows good exposure of the basal frontotemporal lobes, both intra- and extradurally, and reduces brain retraction.

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Mario Ammirati and Florence Perino

✓ The authors report the first case involving trapped epidural air in the spine that mimicked a mass lesion and caused neurological symptoms after epidural corticosteroid injection in the lumbar region. New neurological symptoms developed immediately after injection, and magnetic resonance (MR) imaging demonstrated trapped air displacing the dural sac. After the patient underwent conservative treatment, the new symptoms resolved, and follow-up MR imaging and computed tomography demonstrated resorption of the epidural air in the lumbar region. To limit this problem, the clinician should decrease the amount of air injected in the epidural space or substitute nitrous oxide for air when injecting steroid agents epidurally.