A Review of Neuroendoscopy and Potential Applications in Veterinary Medicine
The endoscope was first developed over 200 yr ago. Endoscopy has since been applied to many disciplines of medicine. Its application to the nervous system was initially slow and not widely accepted and mainly involved the biopsy of tumors and the treatment of hydrocephalus. Several reasons for neuroendoscopy's limited use include inadequate endoscope technology, high skill level required, the advent of the surgical microscope, and the development of other treatments such as ventricular shunting. Over the past 50 yr, improvements in optical glass lenses, fiber optics, and electrical circuitry has led to better equipment and a revival of neuroendoscopy. Neuroendoscopy is now used in many diseases in human medicine including hydrocephalus, neoplasia, and intracranial cysts. This review presents the history of neuroendoscopy, the equipment and technology used, and the possible translation of techniques currently used in human medicine to veterinary medicine.
Introduction
Endoscopy literally means “to look inside” and refers to a minimally invasive diagnostic procedure designed to view the inside of an organ or body region. Not only does it allow direct visual inspection of tissues, but it also allows for photography, videography, and a variety of ways to manipulate the tissue. The number of procedures that have been developed or enhanced by the advent of endoscopy has increased dramatically over the past 50 yr. Many aspects of medicine have benefited from this technology including medical and surgical neurology. The purpose of this review is to provide a concise history and development of neuroendoscopic procedures in human medicine and to discuss the current and potential applications to veterinary medicine.
History of Neuroendoscopy
People, Procedures, and Rudimentary Equipment
The birth of the field of neuroendoscopy grew out of the need to improve visualization and perspective of intracranial anatomy that had previously only been possible with full craniotomy. These ideals quickly outgrew the technology available at the time of its inception.1 Both illumination and magnification were quickly recognized as significant obstacles. Despite few and scattered reports of successful visualization of anatomic detail, most procedures were met with frustration because of these technical limitations.
The first endoscope of any kind was developed by Bozzini in 1806 to explore body cavities and to add a functional perspective to the anatomic knowledge that surgeons and pathologists of the day already held.2 His ideas and his instrument were censored and later rejected by the medical community. It was close to 80 yr before endoscopy resurfaced and regained popularity as a widely accepted and useful tool. This next endoscope to arise was developed by a German urologist named Nitze in 1879. His rigid cystoscope was reportedly a cumbersome device using multiple lenses, described as a miniature “train of lenses,” with a light source at its tip.3 In 1910, L'Espinasse reported the first neuroendoscopic procedure using a cystoscope.4 His work, and the majority of the early work thereafter, was aimed at the treatment of hydrocephalus.
With the growing recognition and understanding of hydrocephalus, more attention was paid to finding successful treatments. Neuroendoscopy was used in many of these early treatments. It was in 1922 that Walter Dandy reported choroid plexectomy via endoscopy as an attempt to decrease cerebrospinal fluid (CSF) production (Figure 1).5 Later that year, Dandy went on to describe ventriculostomy via full craniotomy. Although not an endoscopic technique, it established a new way to reduce the increased intracranial pressure present with hydrocephalus. With this procedure, a small hole was made from the ventricular system into the subarachnoid space as a way to divert excess CSF. The following year, Mixter announced the first successful endoscopic third ventriculostomy (ETV) procedure, which took Dandy's idea of rerouting CSF and incorporated endoscopy in lieu of a full craniotomy.1,4 Over the next 10 yr, results from multiple successful endoscopic procedures were reported including a case series of 42 patients treated by endoscopic choroid plexectomy. Although this procedure was deemed successful at the time, there was a mortality rate of 25% and success rate of only 40%.1,6 In 1935, Scarff introduced an endoscope equipped with electrocautery and an irrigation port.7 Scarff's ETV procedure for hydrocephalus produced dramatic results with a 3 cm decrease in head circumference in only 6 wk. Although the procedure eventually failed, its initial success was convincing evidence that neuroendoscopy held promise. Despite these initially encouraging reports, the technical difficulty, unreliability, poor magnification, and poor illumination left most surgeons seeking other treatment methods.
Citation: Journal of the American Animal Hospital Association 47, 2; 10.5326/JAAHA-MS-5559
Development of Newer Neurosurgical Techniques
While the original developers of these neuroendoscopic techniques continued to perform the procedures to treat hydrocephalus, the overwhelming majority of neurosurgeons never attempted them due to their difficulty, steep learning curve, and relatively high mortality rate. Alternatively, techniques for ventricular shunting were being developed to treat hydrocephalus and the use of the surgical microscope to aid in tumor biopsy and removal became more prevalent.
Ventricular Shunting
The first description of ventricular shunting in 1952 redefined the treatment of hydrocephalus.8 With this procedure, a shunt was inserted into the lateral ventricle, which, using a spring and ball mechanism, drained excess CSF through a tube that was placed either into a blood vessel or body cavity.8,9 This effectively marked the end of the ETV procedure. Reports of ventricular shunting quickly proved that this procedure could be performed with less difficulty and much higher success rates than endoscopic procedures.4 It was not long before advancements such as adjustable pressure shunt valves and antibiotic impregnated tubing were reported.9,10 This rapid advancement of shunting technology made further pursuit of the more difficult endoscopic procedures less appealing.
Microscopic Neurosurgery
Neuroendoscopy was dealt an additional blow by the development of microneurosurgery in the mid-1960s. A variety of intracranial diseases were helped with the aid of the surgical microscope. Primary brain tumors and cysts can cause severe neurologic deficits in a variety of ways, and they are also a common cause of hydrocephalus. Use of a microscope in surgery allowed for more than ample magnification and visualization, factors that previously hindered endoscopy and greatly facilitated tumor removal. Fascination with microscopic neurosurgery centered on the ability to perform more intricate procedures with more precision and less morbidity.11 The scientific literature was flooded with reports of new procedures and techniques utilizing the surgical microscope while reports of neuroendoscopic procedures became sparse.
Rebirth of Neuroendoscopy
Several major factors contributed to renewed interest in neuroendoscopy. First, technological advancements remedied many of the problems that previously limited neuroendoscopy's usefulness. Second, long-term studies began to show that ventricular shunting was not without complications. Lastly, it was realized that other diseases, in addition to hydrocephalus, could also benefit from neuroendoscopy.
Technological Advances
As neurosurgical techniques moved in new directions away from endoscopy, there were several key technological advancements that would eventually lay the groundwork for the reintroduction of modern-day neuroendoscopy. The optical systems used by the early rigid endoscopes posed severe limitations. In 1966, Hopkins and Stortz patented a new type of lens that revolutionized the way rigid endoscopes functioned.12 While a complete explanation of the physics and engineering of optics is beyond the realm of this article, a brief understanding of the progression of optical technology is useful. In basic optical systems such as those used in telescopes, the field of view is limited by the diameter of the lens at the viewer's eye. A large part of the peripheral visual field is lost because those peripheral bundles of light are not properly focused at the eye (Figure 2A). To combat this, a “field” lens was inserted into the system to bend that “lost” portion of light back to the viewer's eye to increase the field of view without increasing the diameter of the objective lens (Figure 2B). Because the rigid endoscope represents the same type of optical system, one can easily see that the small size of the lenses becomes an even larger obstacle.12,13 The basic design of the rigid endoscope employs a series of relay stages throughout the length of the instrument to repeatedly bend the optical information such that the entire field of view reaches the viewer's eye (Figure 3). It was this concept that was first used in Nitze's “train of lenses.” Longer endoscopes require more relay stages and precise location of each of the relay stages is essential. Any slight tilting of a single lens results in dramatic malfunctioning of the instrument.
Citation: Journal of the American Animal Hospital Association 47, 2; 10.5326/JAAHA-MS-5559
Citation: Journal of the American Animal Hospital Association 47, 2; 10.5326/JAAHA-MS-5559
A key advancement that led to the formation of the modern neuroendoscope was the development of gradient index glass. As opposed to conventional lenses, which can only bend light at their surface, this new type of glass had an index of refraction that was not uniform throughout the length of glass. Because of this technology, rays of light travel through the lens in a curved path rather than a straight path.12,14,15 These gradient index glass lenses are much longer, thus eliminating the numerous lens relay stages and glass-to-air interactions. This yielded a brighter image without loss of brightness around the periphery (vignetting). These self-focusing graded index lenses became the basis for the cylindrical lenses used in most modern rigid endoscopes used today.
Another advancement that changed the way endoscopic images were captured and transmitted was the development of charge-coupling devices. This breakthrough technology was developed in 1969 at Bell Laboratories and went on to become the cornerstone of digital photography.16 These charge-coupling devices are essentially silicon chips that function to convert analog data, such as optical information, into electrical current.16 This technology was ideal for low-light environments and was quickly incorporated into endoscopes thereby improving the quality of transmitted images.
Perhaps the largest technologic contribution to the development of the modern endoscope was the creation of fiberoptics. This is the use of glass or plastic fibers to transmit light along its length. The concept and principles of fiberoptic transmission had been known for some time and had become quite useful in telecommunication. Use of optical fibers in lieu of metal wires allowed for transmission over longer distances, at faster rates, with less energy loss in the form of heat. In 1956, researchers at the University of Michigan incorporated fiberoptic bundles into a gastroscope.17 This enabled the light source to be completely separate from the rest of the instrument improving dexterity and decreasing the weight of the instrument. Besides providing a brighter and more efficient light, fiberoptic technology was also used to transmit optic information back to the operator.12
Complications of Ventricular Shunting
Although ventricular shunting had become a relatively easy and effective treatment of hydrocephalus, the procedure also carried with it several common complications such as equipment malfunction, obstruction, infection, and migration.10,18 A retrospective study over 32 yr reported a shunt revision rate of 45%.19 Another more recent retrospective study of 14,455 people in the state of California alone reported an overall complication rate at 5 yr of 32%, and children had an overall complication rate of 52% at 10 yr.20 These statistics left an opening for other technologies and techniques to be explored for the treatment of hydrocephalus.
Hydrocephalus: ETV Revisited and Other Techniques
With the realization of long-term complications and with the unacceptable morbidity and mortality rates associated with ventricular shunting, neurosurgeons began to look for new treatments and revisit old treatments for the management of hydrocephalus. In 2001, the International Study Group on Neuroendoscopy was formed for the purpose of overseeing improvements in techniques and indications for neuroendoscopy.21 With the advancements in endoscopic technology that were being made at the time, renewed interest in the ETV procedure spiked.
The ETV technique offered a more physiologic remedy to the underlying cause of hydrocephalus than the permanent implantation of shunt materials. The ETV procedure was best suited for patients with obstructive hydrocephalus (noncommunicating) in which a blockage in the ventricular system led to a disruption in the normal flow of CSF which subsequently led to accumulation of fluid in the ventricles with compression of cerebral structures and, oftentimes, increased intracranial pressure (i.e., hypertensive hydrocephalus). While ETV was best suited for obstructive hydrocephalus, success had been reported in cases of communicating hydrocephalus as well.
With communicating hydrocephaulus, there is an overall increase in CSF in the ventricular system as well as the subarachoid space. The increase is presumably from a decrease in the absorption of CSF as opposed to an obstruction leading to the fluid accumulation. The exact reason for success of ETV in this situation remains unknown.22–25 Best of all, this procedure gave patients the chance to avoid ventricular shunting procedures and the potential complications associated with them.
The EVT technique is a conceptually straightforward procedure. Briefly, the endoscope is introduced through a small burr hole in the precoronal bone of the skull and passed down a transparent peel-away sheath into the lateral ventricle of the brain.26 The endoscope is then maneuvered through the Foramen of Monroe. This structure is the tubular connection from the lateral ventricles to the third ventricle (which is analogous to the interventricular foramen in veterinary patients). A small fenestration is carefully made in the translucent floor of the third ventricle immediately anterior to the paired mammillary bodies by sharp incision, balloon-tipped catheter, laser, or waterjet dissection. This allows CSF to flow directly from the third ventricle into the subarachnoid space.27 The small fenestration is typically enlarged using a Fogarty balloon catheter (Figure 4) to reduce the overall amount of CSF in the ventricular system and allow resorption of the CSF at the arachnoid villi. The net effect is less fluid in the ventricular system, normalization of intracranial pressure, and alleviation of the associated signs of hydrocephalus. While success rates vary, some authors have reported success rates as high as 81%.22
Citation: Journal of the American Animal Hospital Association 47, 2; 10.5326/JAAHA-MS-5559
Another treatment described for the management of severe hydrocephalus is either microscopic removal or neuroendoscopic coagulation of the choroid plexus.28,29 The endoscopic procedure entails coagulation of the choroid plexus in one or both (if the septum pellucidum is thin or absent) lateral ventricles to markedly reduce the production of CSF. The procedure has been described by some as straightforward and without many complications. While an initial success rate of 66% seems promising, it is possible that subsequent surgical (ventricular shunting) or medical intervention may be needed.28
Cysts
Intracranial cysts have also been treated using neuroendoscopy.30–33 A wide variety of cyst types and locations have been treated including those of the choroid plexus, pineal region, and arachnoid cysts of the quadrigeminal cistern.30–33 Understandably, the approaches and techniques of fenestration/marsupialization are somewhat variable. Thus far, success rates appear good.30,33 For example, in two studies evaluating neuroendoscopic fenestration of arachnoid cysts of the quadrigeminal cistern in 16 and 4 patients, success rates were reported as 87.5% and 100%, respectively.34,35
Tumors
The use of an endoscope to obtain biopsy samples of intraventricular tumors was first reported in 1978.36 Since then, multiple biopsy reports and even tumor resection reports have been published.37–39 Intraventricular tumors and those in close proximity to the ventricular walls are ideal for neuroendoscopy because visualization and maneuverability can be maximized. For more involved cases, neuroendoscopy has been found to be a helpful adjunct to microneurosurgery.40 Undoubtedly, combined neuroendoscopic and microscopic approaches will play an intimate role in procedures such as skull base surgery.40
Complications Associated with Endoscopic Procedures
As with any procedure, the high success rates enjoyed by many neurosurgeons were also met with a number of complications.41 The ETV procedure is the most frequently performed neuroendoscopic procedure. In one study of 222 ETV procedures performed over a 10 yr period, the overall incidence of complications was 11%, and the incidence of transient morbidity, permanent morbidity, and mortality was 7.2%, 1.3%, and 0.9%, respectively.42 Another study of 339 ETV procedures cited a complication rate of 7.7% with an eventual failure rate of 24% (length of follow-up not stated).43 The acute complications were mainly arterial hemorrhage from the basilar artery or its perforators, which often led to fatal hemorrhage. While arterial hemorrhage was a major complication, it was also pointed out that the rate of arterial hemorrhage was directly correlated with the surgeon's experience. That is, all fatalities occurred within the first 20 mo of a surgeon initially performing the procedure.42 This finding underscores a steep learning curve for performing the ETV procedure. Complications of arachnoid cyst fenestration included only 19% transient morbidity with no fatalities in one study.42 While endoscopic choroid plexus coagulation appears to be a relatively straightforward and effective treatment, complications exist such as hemorrhage and collapse of brain tissue. This is due to thin cortical mantle in some patients that require this procedure. In a series of 46 endoscopic treatments (of various types) for intraventricular tumors, no fatalities were reported and there was only a 15.2% transient morbidity rate.42 Numerous reports on intraventricular hemorrhage and its management have been published.44,45
Neuroendoscopy in Veterinary Medicine
Endoscopy has not yet been widely accepted in veterinary neurosurgery despite the fact that some of the same indications for neuroendoscopy in human medicine may exist for veterinary patients. Hydrocephalus, intracranial arachnoid cysts (and arachnoid diverticula), and neoplasia are all possible candidate diseases for neuroendoscopic intervention. Because of the veterinary patient's anatomic size, special consideration needs to be given to proper equipment.
Equipment
Human neurosurgeons rarely encounter anatomy as small as in the veterinary patient. Even though the procedures are practiced and successful in human pediatric patients, the fact remains that veterinary neuroanatomy is often still much smaller. The problem of small anatomy brings with it the need for small instrumentation. All of the procedures discussed thus far are described as using either a rigid or flexible endoscope, and all procedures use additional instrumentation introduced through a working channel. This working channel invariably increases the overall diameter of the endoscope.
The choice of instrumentation is largely based on the procedure being performed as well as the comfort and skill level of the surgeon. As mentioned previously, some of the procedures carry an inherently steep learning curve making careful selection of the correct instrumentation paramount. Initial factors to consider when purchasing an endoscope are cost (which can be sizeable) and whether the scope can be used with, or adapted to, the currently owned endoscopy/laparoscopy equipment. The most important thing to consider when choosing an endoscope is the outer diameter. This measurement corresponds to the minimum amount of tissue that will be traversed and potentially disrupted during the procedure. Several neuroendoscopes offer small outer diameters while retaining a functional working channela–c. While these “working” scopes will be what is needed for most procedures, other instruments are available that are intended more for identification and inspection of the ventricles. These small instruments are malleable fiberoptic scopes without working channels that boast a very small 1.1 mm outer diameterd,e.
Treatment of Hydrocephalus
Hydrocephalus is a common neurologic disorder affecting many breeds of dogs, particularly small and toy breed dogs. Hydrocephalus is strictly defined as an increase in the volume of CSF in the brain or cranial cavity regardless of cause. The two main categories of hydrocephalus described in veterinary patients are compensatory and obstructive, with the latter category having subcategories of acquired and congenital.46
Because the predominant focus of neuroendoscopy described in human medicine involves the management of hydrocephalus, it would only seem logical that some of the endoscopic techniques could be used in veterinary patients. Ventriculoperitoneal shunting has been performed in veterinary medicine for several decades, but some of the same concerns exist in veterinary patients as in human patients. The shunt revision rate has been reported to be between 30–70%,47 and some veterinary neurosurgeons feel this number may be higher. In considering neuroendoscopic intervention, the most obvious concern is the size of the veterinary patient's nervous system. This would pose a significant challenge to procedures such as the ETV, aqueductoplasty (i.e., enlargement of a nonpatent mesencephalic aqueduct), and choroid plexus removal or coagulation.
As previously discussed, the ETV procedure is indicated in cases of obstructive hydrocephalus to establish CSF drainage around a blockage such as a tumor, cystic structure, or stenotic aqueduct leading from the third ventricle to the fourth ventricle. Acquired obstructive hydrocephalus occurs in veterinary patients secondary to conditions such as neoplasia, infectious or noninfectious meningoencephalitis, and possibly even crowding of the caudal fossa.46 The hypertensive hydrocephalus associated with these conditions could possibly be an indication for ETV. Congenital obstructive hydrocephalus is a common condition in veterinary patients and is most often secondary to malformation of the midbrain with resultant stenosis of the mesencephalic aqueduct (Figure 5).46,48 The mesencephalic aqueduct is the tubular portion of the ventricular system that connects the third and fourth ventricles and passes through the midbrain (Figure 6). Although the magnitude of the hydrocephalus seen is variable, hypertensive hydrocephalus may, again, be an indication for ETV. Severe, congenital hydrocephalus has also been seen in dogs without morphologic abnormalities found at necropsy.46 The exact underlying cause of this finding is uncertain. Even though some of these cases appear to have normotensive hydrocephalus, they may still go on to develop clinical signs referable to the hydrocephalus thus potentially warranting treatment of some kind. This same scenario occasionally presents in human medicine and, for reasons that are still unclear, ETV can result in successful outcomes.23 With ETV, CSF is diverted from the third ventricle directly into the subarachnoid space at the level of the rostral brainstem instead of passing through the mesencephalic aqueduct into the fourth ventricle and out into the subarachnoid space via the lateral apertures. The main obstacles to overcome (if applying this method to veterinary patients) are maneuvering the endoscope from the lateral ventricles through the interventricular foramen as well as avoiding trauma to the basilar artery or surrounding vasculature during the actual ventriculostomy. While the indication for this procedure may translate across species, these aforementioned obstacles, as well as the small size of the canine or feline brain in general, may preclude adopting this procedure in veterinary medicine.
Citation: Journal of the American Animal Hospital Association 47, 2; 10.5326/JAAHA-MS-5559
Citation: Journal of the American Animal Hospital Association 47, 2; 10.5326/JAAHA-MS-5559
Cauterization of the choroid plexus is another technique used to treat hydrocephalus in human patients regardless of its underlying cause. This procedure avoids precise navigation down the interventricular foramen, which could prove troublesome, by only cauterizing choroid plexus tissue in the lateral ventricles. As mentioned previously, short-term results in children are promising, although further investigations will be needed to determine the long-term efficacy of this technique. Given the apparent ease and safety of this procedure in children, it may warrant consideration in veterinary patients with severe hydrocephalus.
Intracranial Arachnoid Cyst
Intracranial arachnoid cysts are a relatively uncommon occurrence in veterinary patients but may represent another possible indication for using neuroendoscopy. Although it is possible that these fluid accumulations can develop after trauma or brain inflammation, most investigators believe these cysts are developmental in origin.49 These accumulations of fluid have been increasingly recognized in veterinary medicine since more frequent use of CT and MRI.50,51 Because they are often found incidentally or in regions that do not correspond to clinical signs, their significance is uncertain.50,52 Techniques used in veterinary medicine to treat these cysts include fenestration via craniotomy and cystoperitoneal shunting with the latter technique reporting better success.53,54 Treatment using neuroendoscopic fenestration and marsupialization is reported in human medicine and could possibly translate to veterinary medicine with ease. Introduction of either a conventional neuroendoscope or a smaller, flexible, fiberoptic wand to fenestrate the cyst is a rapid and easy procedure with low morbidity (Dr. Herbert Fuchs, PhD, oral communication, August 2008).
Tumor Removal
Incorporation of neuroendoscopy into the biopsy and resection of intracranial neoplasia has already proven to be of benefit in human medicine. In a recent report of 39 veterinary patients, promising results were found when endoscopy was used to assist in the removal of intracranial tumors.55 In this report, a variety of surgical approaches were used, but in all 39 cases the endoscope was used to remove residual tumor tissue after initial debulking procedures were performed. There were no significant complications associated with the procedures and a median survival of 2,104 days was reported for dogs with forebrain meningiomas and 702 days for dogs with tumors of the caudal fossa.55 Survival data for forebrain meningiomas in this study surpassed all other survival times reported in the veterinary literature. Another report (published by the same author) described endoscopic mass biopsy and/or removal in three animals with no morbidity.56 These two studies suggest that use of endoscopy is apparently safe and may even help improve survival times postoperatively.
Spinal Surgery
Neuroendoscopy need not be limited to intracranial procedures. There are a number of spinal procedures described in the human literature in which endoscopy is used. The use of endoscopy to facilitate visualization during lumbosacral (LS) foraminotomy was recently reported in a prospective experimental study using six dogs.57 LS foraminotomy is a technique used when either static or dynamic collapse of the LS foramen cause compression of the exiting nerves and blood vessels. The hypothesis was that using endoscopic assistance during the procedure would lead to the surgeons making a larger foraminotomy and possibly allowing for the persistence of the enlarged diameter of the intervertebral foramen. The procedure resulted in only mild and transient complications that could not be definitively attributed to the endoscopy. The size of the foramen remained larger than its presurgical size at 12 wk indicating that use of endoscopy can be an adjunct to standard LS decompressive techniques when bony stenosis of the intervertebral foramen is a significant component of the disease.
Conclusion
Neurosurgery in human medicine has been practiced for several hundred years, but has taken enormous steps in only the last several decades. The development of newer technologies, including endoscopy, has revolutionized the management of several common neurologic disorders. Even with microneurosurgery allowing for intricate procedures never before possible and with the emergence of nanoneurosurgery on the near horizon, neuroendoscopy has proven itself an important and viable neurosurgical technique.58 Despite the fact that few procedures described in human medicine utilizing neuroendoscopy have been reported or even attempted in veterinary medicine, the same indications exist. With this being said, it is important to realize that the efficacy of these procedures in veterinary patients is currently not known. Future investigations will need to be performed to establish both safety and efficacy before advocating specific procedures.
Photograph of the ventriculoscope used by Walter Dandy to perform early neuroendoscopic procedures. Photo courtesy of Dr. Edward R. Laws, Jr., and Dr. Daniel Prevedello (taken from Neurosurg Focus 19(6):e3).
A: Diagram of a simple telescope consisting of an objective and an eyepiece lens. The diameter of the eyepiece lens limits the field of view that can be seen by the observer. A cone of light (dashed lines) misses the viewer's eye. This is known as vignetting. B: Insertion of a “field lens” bends the light rays back toward the optical axis to pass through the eyepiece lens. This effectively increases the field of view without incorporating larger diameter lenses.
Diagram of a simple periscope or rigid endoscope consisting of a number of “relay stages” between the objective lens and the eyepiece lens. The number of relay stages depends on the length of the instrument. This concept was the basis for the early endoscope's “train of lenses.”
Photograph showing typical instrumentation needed for the ETV procedure. Rigid endoscope is pictured below. The Fogarty balloon catheter (above) can be used to both make the ventriculostomy fenestration and to enlarge it. Photo courtesy of Dr. George Jallo.
Transverse sections through the brainstem of a 4 mo old dog with developmental hydrocephalus. The mesencephalic aqueduct is absent at the level of the rostral mesencephalon (bottom left section) and there is only a single, malformed rostral colliculus. Photo used with the permission of Drs. de Lahunta and Glass. This figure was published in Veterinary Neuroanatomy and Clinical Neurology, 3rd ed., de Lahunta A, Glass E., p. 71, Copyright Elsevier (2009).
Diagram depicting the canine ventricular system. Figure used with the permission of Drs. de Lahunta and Glass. This figure was published in Veterinary Neuroanatomy and Clinical Neurology, 3rd ed., de Lahunta A, Glass E., p. 57, Copyright Elsevier (2009).
Contributor Notes
