New developments in neurosurgery

Imaging

Advanced imaging techniques like computed tomography (CT) and magnetic resonance imaging (MRI) have changed the landscape for the veterinary neurosurgeon dramatically. CT and MRI scanners are now more commonly available in veterinary practice.

With modern fast helical (64-, 128-) multi-slice CT scanners, imaging of tissue objects with 1 or 2 mm slices is fast (usually less than 30 minutes) and gives a wealth of data. Data storage, data reconstruction and interpretation of hundreds to thousands of slices within a short time span requires specialized knowledge and experience. CT is excellent for bone structures but also for soft tissue (when contrast medium is given) and air-filled cavities. MRI is excellent for (water-rich) soft tissue structures (like brain and spinal cord), but not good for air-filled spaces (like lungs). Likewise, MRI is not the best imaging tool for bone structures but recent research is focusing on MRI bone sequences and experimental versions have already reached the same quality as CT, so ongoing developments may shift the paradigm -CT for bone and MRI for soft tissue-. With respect to MRI and the veterinary field another important issue arises and that is the difference between low field (0.3 Tesla or less) and high field (1.0 to 3.0 Tesla) MRI scanners. In general, low field scanners produce images with low resolution at slow speed. High field scanners produce higher resolution images at a faster speed. The resolution of an image also depends on the size of the tissue object that is scanned. Therefore the quality of images that are produced by low field scanners of small animals like cats and small dogs (<10 kg) may not be sufficient to show detailed pathology in e.g. brain or spinal cord in comparison with high field scanners. This knowledge should be used responsibly by radiologists and managers of low field scanners when cats or small dogs are referred for MRI to prevent re-scanning at other institutions with high field scanners (with unnecessary anesthetic burden for the patient and financial burden for the owner).

The true value of CT and MRI for the neurosurgeon lies in the reconstructions in sagittal and axial planes, or multiplanar reconstructions (MPR) allowing to scroll through tissue objects from all angles. For bone structures like spine and skull, 3D reconstructions allow the surgeon to look at the pathology from all angles, and to prepare the surgical approach in silico, and with software tools like ‘knife’, even to practice surgical excisions in silico. The surgeon should not be limited by expensive software licences for Picture Archiving and Communication System (PACS) systems. The medical field has realized this for a long time and therefore freeware software tools are available on the web that allow the surgeon to download software tools at no or very low cost and work with DICOM® (Digital Imaging and Communications in Medicine). DICOM is the international standard to transmit, store, retrieve, print, process, and display medical imaging information. DICOM makes medical imaging information interoperable, integrates image-acquisition devices, PACS, workstations, and printers from different manufacturers, is actively developed and maintained to meet the evolving technologies and needs of medical imaging, and is free to download and use. There are many free DICOM viewers available on the internet but common viewers that are used by radiologists, neurologists and neurosurgeons are:

RadiAnt® (https://www.radiantviewer.com): Windows based dicom viewer.
OsiriX® (https://www.osirix-viewer.com): Apple based dicom viewer.
The Horos Project® (https://horosproject.org): Apple based dicom viewer.
Horos and OsiriX are the top two medical image viewers for Apple computers. However, the two products have different functionalities and work very differently in many respects. To read more in the differences between Horos and OsiriX , please see:https://www.purview.net/blog/horos-v.-osirix-whats-the-difference

Neurosurgical indications

The most common neurosurgical indications of the cranium are neoplasia (meningioma and glioma), trauma (skull fracture, bite wounds), hydrocephalus, and brain abscess.
The most common neurosurgical indications of the spine have been degenerative disorders like disc herniation (cervical and thoracolumbar disc herniation, caudal cervical spondylomyelopathy, degenerative lumbosacral stenosis), spinal neoplasia, spinal trauma (fracture and luxation) and infection (discospondylitis). Due to the availability of advanced imaging modalities like CT and MRI in veterinary practice and further veterinary specialization, more and more CT and MRI are performed in dogs and cats with neurological signs. This has resulted in more frequent diagnosis of anomalies and the question then arises whether these can be treated surgically. Two new groups of disorders are more frequently seen and have become part of the list of neurosurgical indications, i.e., spinal cyst and spinal deformity.