German physician Saemisch introduced compound lens magnication to medicine in 1876. In the early part of the 20th century, Carl Nylen, a 30-year-old Swedish otolaryngologist, inspired by Maier and Lion’s observations of endolymph movement, conceived and built the world’s first operative microscope. In 1921 he used his monocular microscope for humans for the first time in a case of chronic otitis media. Gunnar Holmgren, Nylen’s chief at the Stockholm clinic, improved on Nylen’s monocular design and attached a light, creating the rst binocular surgical microscope in 1922. The original surgical microscopes were crude, usually requiring fixation to the bony structures of the skull 1).
During the ensuing decades, otolaryngologists and ophthalmologists continued to refine and expand the use of the operating microscope.
Theodore Kurze was the first to use the operating microscope in the discipline of neurosurgery. In 1957 he used the device to remove a vestibular schwannoma in a 5-year-old patient in Los Angeles. The procedure was a success, but Kurze grappled with the draping technique. He tried several materials and techniques including turkey bags with elastics to fit the microscope handles—an attempt that produced immense heat and smoke in one case
He continued his refinements and worked to establish the world’s first cranial base microsurgical laboratory. His work with the microscope introduced many neurosurgeons to the vast possibilities of such a tool. As Kurze proceeded with his work, an industrious and insightful neurosurgeon began his own observations and practical utilization of the operating microscope on the opposite coast: Raymond Madiford Peardon Donaghy
Information supplied by an image-guidance system can be superimposed on the operating microscope oculars or on a screen, generating augmented reality. Recently, the outline of a patient's head and skull, injected in the oculars of a standard operating microscope, has been used to check the registration accuracy of image guidance.
A commercially available image-guidance system and a standard operating microscope were used. Segmentation of the brain surface and cortical blood vessel relief was performed manually on preoperative computed tomography and magnetic resonance images. The overlay of segmented digital and real operating-microscope images was used to monitor image-guidance accuracy. Adjustment for brain shift was performed by manually matching digital images on real structures.
Experimental manipulation on a phantom proved that the brain surface relief could be used to restore accuracy if the primary registration shifted. Afterward, the technique was used to assist during surgery of 5 consecutive patients with 7 deep-seated brain tumors. The brain surface relief could be successfully used to monitor registration accuracy after craniotomy and during the whole procedure. If a certain degree of brain shift occurred after craniotomy, the accuracy could be restored in all cases, and corticotomies were correctly centered in all cases.
The proposed method was easy to perform and augmented image-guidance accuracy when operating on small deep-seated lesions 2).