Introduction: Confocal endomicroscopy previouly used to assess histopathologic features of intracranial lesions. We sought to assess the feasibility of handheld confocal endomicroscopy to provide histologic information of normal brain.

Methods: Three adult Yorkshire swine were used to investigate the utility of the confocal endomicroscope to image features of normal brain tissue. Craniectomy and C1-5 laminectomy were performed on each anesthetized animal. The brain and upper cervical spinal cord were excised with the surrounding dura mater. Using a tissue slicer, 5-mm thick slides were cut and soaked in 0.01% acridine orange for 2 minutes before imaging. Imaged anatomical areas were carefully documented and marked with tissue ink for correlation of H&E-stained sections to confocal images.

Results: Frontal cortex was characterized by dark neuron cell bodies surrounded by brighter and smaller cells, possibly glial cells. Imaging of frontal white matter revealed axons and multiple bright fluorescent cells, which were possibly glial cells. The caudate nucleus consisted of dark white matter tracts and neuron cell bodies over a brighter background. The walls of the lateral ventricle showed a characteristic honeycomb pattern of intensely fluorescent ependymal cells. Prominent crossing fibers were evident in the pons. Imaging of the medulla revealed crossing fiber tracts in different planes. In the cerebellum, Purkinje cells appeared as large dark cells. These cells were identified adjacent to the granular cell layer and white matter tracts. The gray matter of the spinal cord consisted of large, dark neuron cell bodies. Images from the central canal were outlined with intensely fluorescent ependymal cells. White matter appeared as cross-sectioned myelinated axons.

Conclusions: Confocal endomicroscopy was effective at showing characteristic histoarchitectural patterns in different areas of normal brain. Thus handheld confocal microscopy is able to distinguish between normal brain and neoplastic tissue intraoperatively, which is an essential clinical capability for ensuring completeness of glioma resection.

Patient Care: Handheld confocal microscopy is able to distinguish between normal brain and neoplastic tissue intraoperatively, which is an essential clinical capability for ensuring completeness of glioma resection.

Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the importance of handheld confocal endomicroscopy, 2) Discuss, in small groups, intraoperative distinguishing of normal brain and tumor, 3) Identify an effective technology for intraoperative diagnosis

References: Eschbacher J, Martirosyan NL, Nakaji P, Sanai N, Preul MC, Smith KA, et al: In vivo intraoperative confocal microscopy for real-time histopathological imaging of brain tumors. J Neurosurg 116:854-860, 2012 Martirosyan NL, Cavalcanti DD, Eschbacher JM, Delaney PM, Scheck AC, Abdelwahab MG, et al: Use of in vivo near-infrared laser confocal endomicroscopy with indocyanine green to detect the boundary of infiltrative tumor. J Neurosurg 115:1131-1138, 2011