The effect of laparoscopy on intracranial pressure as measured by optic nerve sheath diameter: A review.

Laparoscopic surgery has many benefits over open surgery including lower complication rates, and shorter duration and lower cost of hospitalization. However, recent human literature suggests laparoscopy and carbon dioxide insufflation can result in intracranial hypertension. Invasive monitoring of intracranial pressure is not routinely performed in veterinary medicine, and ultrasonographic evaluation of the optic nerve sheath has been employed as an indirect measure of intracranial pressure in many species. The optic nerve sheath is continuous with the meninges of the brain and becomes distended with intracranial hypertension. Optic nerve sheath diameter is a reliable and consistent measure of intracranial pressure and has been utilized in humans to evaluate patients for intracranial hypertension secondary to laparoscopy and capnoperitoneum. No thorough evaluation of the effects of laparoscopy on intracranial pressure has been performed in dogs. Ultrasonographic evaluation of the optic nerve sheath is a safe, non-invasive, and inexpensive procedure that may allow for the evaluation of intracranial pressure without the need for invasive monitoring systems. As laparoscopic procedures are performed increasingly often, this review aims to inform the reader on the effects of capnoperitoneum and to facilitate appropriate patient selection, anesthetic considerations, and surgical planning.

L'effet de la laparoscopie sur la pression intracrânienne mesurée par le diamètre de la gaine du nerf optique : une revue. La chirurgie laparoscopique présente de nombreux avantages par rapport à la chirurgie ouverte, notamment des taux de complications plus faibles, une durée d'hospitalisation plus courte et un coût moindre. Cependant, la littérature humaine récente suggère que la laparoscopie et l'insufflation de dioxyde de carbone peuvent entraîner une hypertension intracrânienne. La surveillance invasive de la pression intracrânienne n'est pas systématiquement effectuée en médecine vétérinaire, et l'évaluation échographique de la gaine du nerf optique a été utilisée comme mesure indirecte de la pression intracrânienne chez de nombreuses espèces. La gaine du nerf optique est continue avec les méninges du cerveau et se distend avec l'hypertension intracrânienne. Le diamètre de la gaine du nerf optique est une mesure fiable et cohérente de la pression intracrânienne et a été utilisé chez l'homme pour évaluer les patients atteints d'hypertension intracrânienne secondaire à la laparoscopie et au capnopéritoine. Aucune évaluation approfondie des effets de la laparoscopie sur la pression intracrânienne n'a été réalisée chez le chien. L'évaluation échographique de la gaine du nerf optique est une procédure sûre, non invasive et peu coûteuse qui peut permettre l'évaluation de la pression intracrânienne sans avoir besoin de systèmes de surveillance invasifs. Les procédures laparoscopiques étant de plus en plus pratiquées, cette revue vise à informer le lecteur sur les effets du pneumopéritoine et à faciliter la sélection appropriée des patients, les considérations anesthésiques et la planification chirurgicale.(Traduit par Dr Serge Messier).

Preliminary evaluation of a non-invasive device for monitoring intracranial pressure waveforms in dogs.

OBJECTIVES: The objective of this study was to compare waveforms obtained with a new device for the non-invasive monitoring of intracranial pressure (ICP) in dogs with and without neurological disease. MATERIALS AND METHODS: This prospective study was conducted on both neurologically normal dogs and dogs with neurological diseases. First, non-invasive ICP waveforms were recorded in normal dogs using the Braincare® BcMM 2000 monitor while the dogs were under general anaesthesia induced for procedures unrelated to this study. The dogs were positioned in lateral recumbency, and the sensor was placed over the skin of the parietal region. Secondly, non-invasive ICP waveforms were monitored in dogs with brain and spinal disease until waveforms with characteristic peaks were acquired. All the recorded signals were amplified, filtered and digitalized, by the device, and then transferred to a computer for analysis. RESULTS: Normal pulse waveforms indicating normal brain complacency were observed in eight neurologically normal dogs. In six dogs with brain disease, abnormal pulse waveforms were observed suggesting increased ICP and decreased brain complacency. Four dogs with spinal disease undergoing myelography, had normal waveforms before contrast medium injection and abnormal pulse waveforms during contrast medium injection, indicating a potential increase in ICP. CLINICAL SIGNIFICANCE: Based on these preliminary observations, this method was capable of detecting abnormal pulse waveforms that suggested increased ICP.

Study of the effect of anaesthesia on the canine ultrasonographic optic nerve sheath diameter.

OBJECTIVES: To investigate the effects of anaesthetic duration and serial anaesthetic events on optic nerve sheath diameter in a population of dogs without intracranial disease using point-of-care ultrasonography. MATERIALS AND METHODS: Client-owned dogs requiring advanced head imaging were prospectively enrolled. Exclusion criteria included signs of elevated intracranial pressure, glaucoma and optic nerve disease. Using a transpalpebral technique, two optic nerve sheath diameter measurements were recorded for each eye at three timepoints: following premedication, after induction within 7 minutes and before discontinuing isoflurane. Mixed model analysis was used to characterise optic nerve sheath diameter behaviour and investigate the effects of anaesthetic duration, bodyweight and anaesthetic protocol, age and sex. RESULTS: Fourteen dogs of various ages, breeds and bodyweights were enrolled. A positive linear relationship was detected between body weight and optic nerve sheath diameter. In 12 of 14 dogs, the optic nerve sheath diameter increased from measurements taken after premedication when compared to measurements taken after induction within 7 minutes. In a subset of patients, measurements subsequently decreased when anaesthetic duration exceeded 120 minutes. Age, side, sex, final body temperature, blood pressure and anaesthetic protocol did not significantly affect optic nerve sheath diameter. No significant association was noted between optic nerve sheath diameter and end-tidal carbon dioxide after induction and before discontinuing isoflurane. CLINICAL SIGNIFICANCE: When using point-of-care ultrasound, a transient increase in optic nerve sheath diameter occurs between premedication and within 7 minutes following induction, regardless of bodyweight. This should be taken into consideration when serial monitoring is performed.

Relationship between the ratio of optic nerve sheath diameter to eyeball transverse diameter and morphological characteristics of dogs.

OBJECTIVE: To assess the feasibility of ocular ultrasonography for measurement of the ratio of optic nerve sheath diameter (ONSD) to eyeball transverse diameter (ETD) in dogs with various morphologies and to evaluate the interobserver reliability of the ONSD/ETD ratio and its correlation with various morphological variables. ANIMALS: 45 healthy dogs of various breeds. PROCEDURES: Height, head circumference, body weight, body condition score, intraocular pressure, and blood pressure were recorded for each dog. Unsedated dogs underwent bilateral ocular ultrasonography once. A veterinarian and board-certified ophthalmologist who were unaware of subject signalment independently reviewed the ultrasonographic videos and selected 1 image for each eye on which the ETD and ONSD were measured. The ONSD/ETD ratio was calculated and compared between the 2 observers. Correlations between the ONSD/ETD ratio and various physiologic and morphological variables were assessed. RESULTS: 172 ONSD/ETD ratios were recorded. The ONSD/ETD ratio was calculated for at least 1 eye for 44 of the 45 (98%) dogs. Mean ± SD time required to complete the ultrasonographic examination was 90 ± 30 seconds (range, 15 seconds to 3 minutes). The mean ± SD ONSD/ETD ratio was 0.17 ± 0.01 (range, 0.15 to 0.20). The ONSD/ETD ratio did not differ significantly between the left and right eyes or the 2 observers and was not correlated with any of the variables assessed. CONCLUSIONS AND CLINICAL RELEVANCE: Ocular ultrasonography was a rapid, noninvasive, and reliable method for measurement of the ONSD/ETD ratio. The ONSD/ETD ratio did not appear to be influenced by dog morphology.

Evaluation of transpalpebral ultrasonographic measurement of optic nerve sheath diameter for indirect assessment of intracranial pressure in anesthetized and standing healthy adult horses.

OBJECTIVE: To determine whether an association exists between direct intracranial pressure (ICP) measurement and ultrasonographic measurement of optic nerve sheath diameter (ONSD) in anesthetized and standing horses. DESIGN: Cross-sectional study performed on a convenience sample of healthy adult horses. SETTING: University teaching hospital. ANIMALS: Eight adult horses donated to the University. Enrolled horses were free of abnormalities on physical examination, CBC, neurological evaluation, and ophthalmological examination. MEASUREMENTS AND MAIN RESULTS: Horses were anesthetized in lateral recumbency for placement of an ICP transducer. Three head positions (neutral, elevated, and lowered) were used to alter ICP. ICP and ONSD in 2 directions (D1 and D2) were recorded at 5 and 10 minutes after position change to elevated and lowered. ICP and ONSD measurements were repeated in standing sedated horses 24-36 hours after recovery from anesthesia. Linear regressions were performed with ICP as the dependent variable and ONSD as the independent variable by head position and times. Linear regressions were also performed for change from neutral under anesthesia, with ONSD as the independent variable and ICP as the dependent variable, by head position and times. Significance was set at P < 0.05. There was a moderate association between ICP and ONSD in horses with head lowered at 5 and 10 minutes (R2 values = 63%-78%) and weak association in head elevated at 10 minutes (R2 values = 56%-63%). There was a weak association between change from neutral ICP and change from neutral ONSD in the elevated anesthetized position at 10 minutes for summed D1 + D2 (R2  = 33%). CONCLUSIONS: Consistent associations between direct ICP and ONSD in anesthetized or standing horses were not observed. This inconsistency limits the clinically utility of transpalpebral ultrasonographic ONSD measurement for ICP monitoring in horses.

MRI of the optic nerve sheath and globe in cats with and without presumed intracranial hypertension.

OBJECTIVES: The study aimed to: (1) test MRI repeatability of measurements of optic nerve sheath diameter (ONSD), optic nerve diameter (OND) and eye globe transverse diameter (ETD); (2) investigate the associations between the OND, ONSD and ETD; (3) assess whether these measurements are affected by age or body weight; and (4) test the association between ONSD, OND, ETD and ONSD:ETD ratio with presumed intracranial pressure (ICP) status. METHODS: This was a retrospective and blinded study where patients were allocated to presumed normal or intracranial hypertension groups based on MRI findings. The ONSD and ETD were measured and recorded. Interclass correlation coefficient (ICC) was calculated to investigate interobserver agreement. Data were analysed using the Pearson correlation coefficient, two-sample t-test and general linear model ANOVA. RESULTS: Seventy-seven cats were included, 62 with presumed normal ICP and 15 with presumed intracranial hypertension. The ICC showed moderate-to-good reliability for all measurements. Positive correlations were identified for: (1) ETD and weight; (2) ONSD and age; (3) OND and age; (4) ONSD and ETD; (5) ONSD:ETD ratio and presumed ICP status; and (6) ONSD and presumed ICP status. No difference was detected between the presumed normal and intracranial hypertension groups and ONSD, as well as ONSD:ETD ratio and presumed ICP status when patient age was considered. CONCLUSIONS AND RELEVANCE: The measurement of the ONSD and the ONSD:ETD ratio on T2-weighted MRI might not be reliable as non-invasive tests for diagnosing intracranial hypertension in cats.

Comparison of the effects of 7.2% hypertonic saline and 20% mannitol on electrolyte and acid-base variables in dogs with suspected intracranial hypertension.

BACKGROUND: Hyperosmolar agents frequently are used to decrease intracranial pressure but their effects on electrolyte and acid-base variables have not been prospectively investigated. OBJECTIVES: Compare duration and magnitude of changes in electrolyte and acid-base variables after hyperosmolar treatment. ANIMALS: Twenty-eight client-owned dogs with intracranial hypertension caused by various pathologies. METHODS: Prospective, randomized, nonblinded, experimental cohort study. Fifteen dogs received a single dose (4 mL/kg) of 7.2% hypertonic saline (HTS), 13 dogs received 20% mannitol (MAN) 1 g/kg IV. Electrolyte and acid-base variables were measured before (T0 ), and 5 (T5 ), 60 (T60 ), and 120 (T120 ) minutes after administration. Variables were compared between treatments and among time points within treatment groups. RESULTS: Mean plasma sodium and chloride concentrations were higher after HTS than MAN at T5 (158 vs 141 mEq/L; 126 vs 109 mEq/L) and significant differences were maintained at all time points. After HTS, plasma sodium and chloride concentrations remained increased from T0 at all time points. After MAN, plasma sodium and chloride concentrations decreased at T5 , but these changes were not maintained at T60 and T120 . Plasma potassium concentration was lower at T5 after HTS compared with T0 (3.6 vs 3.9 mEq/L) and compared to MAN (3.6 vs 4.1 mEq/L). At T60 and T120 , plasma ionized calcium concentration was lower after HTS than MAN (1.2 vs 1.3 mmol/L). No significant differences were found in acid-base variables between treatments. CONCLUSIONS AND CLINICAL IMPORTANCE: At the administered dose, dogs receiving HTS showed sustained increases in plasma sodium and chloride concentrations, whereas dogs receiving MAN showed transient decreases. Future studies should assess the effects of multiple doses of hyperosmolar agents on electrolyte and acid-base variables.

Evaluation of basilar artery and cerebrospinal fluid dynamics using phase-contrast MRI: Comparison between mannitol and isotonic saline solution.

Increased intracranial pressure (ICP) can cause irreversible pathological changes in the canine brain and can be life-threatening, so prompt diagnosis and therapeutic responses are warranted. The purposes of this prospective experimental study were to evaluate phase-contrast MRI (PC-MRI) as a non-invasive method for quantifying cerebrospinal fluid (CSF) and basilar artery flow, and to assess effects of intravenous administration of hypertonic fluid. A PC-MRI scan was acquired for six healthy Beagle dogs at the level of the mesencephalic aqueduct. Either 1.0 g/kg mannitol or isotonic saline solution was administered intravenously for 15 min each at a matched dose volume of 5 mL/kg. Basilar artery and CSF flow rates were measured and their values compared between mannitol and isotonic saline solution groups before administration, and subsequently every 15 min for 2 h post-administration. The CSF dynamics were further assessed by measuring repeat flow from the caudal to rostral direction and the rostral to caudal direction as the number of waves. No significant difference was observed in basilar or and CSF flow velocity between the two groups (P > .05). However, administration of isotonic saline solution tended to increase basilar artery velocity slightly over time, while CSF velocity remained unchanged. In the mannitol group, CSF wave forms tended to be reduced at 60 and 75 min (P > .05). Findings from this preliminary study indicated that it is feasible to measure the dynamics of CSF and basilar artery flow by PC-MRI, but no flow differences could be detected for mannitol versus isotonic saline administration.

Comparison of direct measurement of intracranial pressures and presumptive clinical and magnetic resonance imaging indicators of intracranial hypertension in dogs with brain tumors.

BACKGROUND: Intracranial hypertension (ICH) is often presumptively diagnosed based on clinical or imaging findings. Clinical or imaging surrogates of ICH are not usually validated with reference standard direct intracranial pressure (dICP) recordings. HYPOTHESES: Dogs with brain magnetic resonance imaging (MRI) or clinical features of presumed ICH would have higher dICP than dogs lacking those features. ANIMALS: Twenty dogs with gliomas and 3 normal controls. METHODS: Prospective, convenience study. Dogs were presumptively categorized with normal ICP or ICH from scores generated from described clinical and brain MRI indicators of ICH. dICP was recorded in anesthetized dogs using an intraparenchymal microsensor and compared between groups. RESULTS: dICP was not different between control (10.4 ± 2.1 mm Hg) and dogs with glioma (15.6 ± 8.3 mm Hg), or between dogs in clinically predicted ICP groups. Compared with dogs with MRI-predicted normal ICP, MRI-predicted ICH dogs had higher dICP (10.3 ± 4.1 versus 19.2 ± 7.9 mm Hg, P = .004), larger tumors (1.45 ± 1.2 versus 5.71 ± 3.03 cm3 , P = .0004), larger optic nerve sheath diameters, and 14/14 (100%) displayed structural anatomical shifts on MRI. At a dICP threshold of 15 mm Hg, the sensitivity of MRI for predicting ICH was 90% and the specificity 69%. CONCLUSIONS AND CLINICAL RELEVANCE: dICP measurements are feasible in dogs with brain tumors. MRI features including brain herniations, mass effect, and optic nerve size aid in the identification of dogs with ICH. Clinical estimation of ICP did not discriminate between dogs with and without ICH.

Repeatability of ultrasound examination of the optic nerve sheath diameter in the adult cat: comparison between healthy cats and cats suffering from presumed intracranial hypertension.

OBJECTIVES: The objectives of this study were to test: (1) the repeatability of ultrasonographic examination of the optic nerve sheath diameter (ONSD) in the cat; (2) the association between the ONSD and age, sex and body weight in healthy cats; and (3) the difference in the ONSD between healthy cats and those suffering from presumed intracranial hypertension (ICH). METHODS: This study had a prospective, blinded, observational cross-sectional study design. Two groups of animals were considered: healthy cats (group A) and cats with a diagnosis of presumed ICH (group B). The ONSD was evaluated, measured and compared between the two groups via an ultrasonographic transpalpebral approach. Repeatability of the procedure was evaluated through the intraclass correlation coefficient (ICC). Data were statistically compared using the Student's t-test and linear regression analysis. RESULTS: A strong inter- and intraobserver ICC indicating good repeatability was observed. The interobserver ICC was 0.965 (P <0.05) for the right eye and 0.956 (P <0.05) for the left eye. The intraobserver ICC was 0.988 (P <0.05) and 0.984 (P <0.05) for the right and left eyes, respectively. In healthy cats the mean ± SD ONSD was 1.23 ± 0.11 mm (range 1-1.47 mm) and 1.23 ± 0.10 (range 1-1.4 mm) for right and left eyes, respectively. The ONSD was not related to sex or weight; a weak relationship was observed with age. In group B, the mean ONSD was 1.68 ± 0.13 mm (range 1.5-1.9 mm) and 1.61 ± 0.15 mm (range 1.4-1.9 mm) for the right and left eyes, respectively. In group B, the ONSD was statistically significantly larger than in group A, the healthy cats (P <0.001). CONCLUSIONS AND RELEVANCE: The transpalpebral ultrasonographic technique is a non-invasive, feasible and reproducible method to measure ONSD both in healthy cats and in cats suffering from suspected ICH.

Impact of intracranial hypertension on the short-term prognosis in dogs undergoing brain tumor surgery.

The present study used data from anesthetic records to analyze variables of intracranial pressure (ICP) during brain tumor surgery or in the early postoperative period as prognostic indicators in dogs. Data from 17 dogs which were scheduled to undergo elective craniotomy for brain tumor surgery from 2009 to 2012 were included. Of these, five (29.4%) died during 14 days after the surgery because of respiratory failure following pneumonia (n=2), euthanasia due to difficulty in treatment of status epilepticus (n=1), tumor-bed hematoma (n=1), and unknown reason (n=1). In the 12 surviving dogs, neurological signs were improved or resolved at discharge. All dogs were administered midazolam and droperidol-fentanyl as premedication. General anesthesia was induced using propofol maintained on isoflurane and oxygen. Direct ICP was obtained via a Codman Microsensor strain gauge transducer. ICP hypertension (>13 mmHg) measured after 15 min of recovery from the moment after discontinuation of anesthesia by turning off the vaporizer dial was associated with poor prognosis (odds ratio, 20.00; 95% confidence interval, 1.39-287.60, P=0.028). This suggests that intracranial pressure influences the postoperative mortality rate in dogs undergoing brain tumor surgery.

Transcranial Doppler Ultrasound Examination in Dogs with Suspected Intracranial Hypertension Caused by Neurologic Diseases.

BACKGROUND: Transcranial Doppler ultrasound examination (TCD) is a rapid, noninvasive technique used to evaluate cerebral blood flow and is useful for the detection of intracranial hypertension in humans. However, the clinical usefulness of TCD in diagnosing intracranial hypertension has not been demonstrated for intracranial diseases in dogs. OBJECTIVES: To determine the association between the TCD variables and intracranial hypertension in dogs with intracranial diseases. ANIMALS: Fifty client-owned dogs with neurologic signs. METHODS: Cross-sectional study. All dogs underwent TCD of the basilar artery under isoflurane anesthesia after magnetic resonance imaging (MRI). Dogs were classified into 3 groups based on MRI findings: no structural diseases (group I), structural disease without MRI evidence of intracranial hypertension (group II), and structural disease with MRI evidence of intracranial hypertension (group III). The TCD vascular resistance variables (resistive index [RI], pulsatility index [PI], and the ratio of systolic to diastolic mean velocity [Sm/Dm]) were measured. RESULTS: Fifteen, 22, and 13 dogs were classified into groups I, II, and III, respectively. Dogs in group III had significantly higher Sm/Dm (median, 1.78; range, 1.44-2.58) than those in group I (median, 1.63; range, 1.43-1.75) and group II (median, 1.62; range, 1.27-2.10). No significant differences in RI and PI were identified among groups. CONCLUSIONS AND CLINICAL IMPORTANCE: Our findings suggest that increased Sm/Dm is associated with MRI findings of suspected intracranial hypertension in dogs with intracranial diseases and that TCD could be a useful tool to help to diagnose intracranial hypertension.

Relationships among neuroscore, magnetic resonance imaging features, and intracranial pressure in sheep affected by slow-growing brain lesions.

Diagnosing high intracranial pressure by clinical and diagnostic imaging is particularly challenging for chronic or slow-growing lesions. The aim of this prospective case-control study is to determine whether the neuroscore and brain magnetic resonance imaging (MRI) are related to the direct measurement of intracranial pressure in sheep affected by intracranial slow-growing lesions due to chronic cerebral coenurosis (Coenurus cerebralis). Seventeen affected and 10 control sheep were included. All animals underwent a neurological examination, MRI of the brain, and direct measurement of intracranial pressure. The severity of clinical signs and MRI findings were scored. Data were statistically analyzed. The invasive intracranial pressure value was higher in affected animals. A severely altered neuroscore is related to an increased intracranial pressure beyond the normal threshold (P < 0.05). The volume of the calvarium was larger in affected animals than in control animals (P = 0.0001) and was positively influenced by the presence and volume of the parasitic cyst (r = 0.7881, P < 0.01). Several degrees of deviation and deformation of both the ventricular system and brain parenchyma were detected by MRI. Subjective MRI findings were not associated with intracranial hypertension. In conclusion, this study shows that in sheep affected by slow-growing lesions, severe alterations in the neuroscore and the results of objective MRI are related to an increased intracranial pressure beyond the normal threshold.

Comparison of the effects of 7.2% hypertonic saline and 20% mannitol on whole blood coagulation and platelet function in dogs with suspected intracranial hypertension - a pilot study.

BACKGROUND: Hyperosmolar therapy with either mannitol or hypertonic saline (HTS) is commonly used in the treatment of intracranial hypertension (ICH). In vitro data indicate that both mannitol and HTS affect coagulation and platelet function in dogs. The aim of this study was to compare the effects of 20% mannitol and 7.2% HTS on whole blood coagulation using rotational thromboelastometry (ROTEM®) and platelet function using a platelet function analyzer (PFA®) in dogs with suspected ICH. Thirty client-owned dogs with suspected ICH needing osmotherapy were randomized to receive either 20% mannitol (5 ml/kg IV over 15 min) or 7.2% HTS (4 ml/kg IV over 5 min). ROTEM® (EXTEM® and FIBTEM® assays) and PFA® analyses (collagen/ADP cartridges) were performed before (T0), as well as 5 (T5), 60 (T60) and 120 (T120) minutes after administration of HTS or mannitol. Data at T5, T60 and T120 were analyzed as a percentage of values at T0 for comparison between groups, and as absolute values for comparison between time points, respectively. RESULTS: No significant difference was found between the groups for the percentage change of any parameter at any time point except for FIBTEM® clotting time. Within each group, no significant difference was found between time points for any parameter except for FIBTEM® clotting time in the HTS group, and EXTEM® and FIBTEM® maximum clot firmness in the mannitol group. Median ROTEM® values lay within institutional reference intervals in both groups at all time points, whereas median PFA® values were above the reference intervals at T5 (both groups) and T60 (HTS group). CONCLUSIONS: Using currently recommended doses, mannitol and HTS do not differ in their effects on whole blood coagulation and platelet function in dogs with suspected ICH. Moreover, no relevant impairment of whole blood coagulation was found following treatment with either solution, whereas a short-lived impairment of platelet function was found after both solutions.

Noninvasive assessment of intracranial pressure in dogs by use of biomechanical response behavior, diagnostic imaging, and finite element analysis.

UNLABELLED: OBJECTIVE :To develop a novel method for use of diagnostic imaging, finite element analysis (FEA), and simulated biomechanical response behavior of brain tissue in noninvasive assessment and estimation of intracranial pressure (ICP) of dogs. SAMPLE: MRI data for 5 dogs. PROCEDURES: MRI data for 5 dogs (1 with a geometrically normal brain that had no detectable signs of injury or disease and 4 with various degrees of geometric abnormalities) were obtained from a digital imaging archiving and communication system database. Patient-specific 3-D models composed of exact brain geometries were constructed from MRI images. Finite element analysis was used to simulate and observe patterns of nonlinear biphasic biomechanical response behavior of geometrically normal and abnormal canine brains at various levels of decreasing cerebral perfusion pressure and increasing ICP. RESULTS: Changes in biomechanical response behavior were detected with FEA for decreasing cerebral perfusion pressure and increasing ICP. Abnormalities in brain geometry led to observable changes in deformation and biomechanical response behavior for increased ICP, compared with results for geometrically normal brains. CONCLUSIONS AND CLINICAL RELEVANCE: In this study, patient-specific critical ICP was identified, which could be useful as a method to predict the onset of brain herniation. Results indicated that it was feasible to apply FEA to brain geometry obtained from MRI data of clinical patients and to use biomechanical response behavior resulting from increased ICP as a diagnostic and prognostic method to noninvasively assess or classify levels of brain injury in clinical veterinary settings.

Altered states of consciousness in small animals.

Impaired states of consciousness can be relatively easily identified, although it can occasionally be difficult to assess whether there is a pure disorder of wakefulness or awareness. Regardless, such impairments represent dysfunction of the brainstem and or cerebrum. Acute and severe impairments of consciousness can require immediate assessment, in part currently performed using the modified Glasgow coma scoring system, and emergency stabilization. The prognosis is always guarded and highly sensitive to the underlying etiology.

Magnetic resonance imaging signs of presumed elevated intracranial pressure in dogs.

The aim of this study was to describe magnetic resonance imaging (MRI) findings associated with presumed elevated intracranial pressure (ICP) in dogs and to evaluate whether MRI could be used to discriminate between dogs with and without elevated ICP. Of 91 dogs that underwent cranial MRI examination, 18 (19.8%) were diagnosed with elevated ICP based on neurological examination, fundoscopy and transcranial Doppler ultrasonography. The MRI findings that showed the strongest association with elevated ICP were mass effect (odds ratio [OR], 78.5), caudal transtentorial herniation (OR, 72.0), subfalcine herniation (OR, 45.6), perilesional oedema (OR, 34.0), displacement of the lamina quadrigemina (OR, 27.7) and effacement of the cerebral sulci (OR, 27.1). The presence of any two or more of the following MRI findings identified elevated ICP with a sensitivity of 72% and a specificity of 96%: compression of the suprapineal recess, compression of the third ventricle, compression of the fourth ventricle, effacement of the cerebral sulci and caudal transposition of the lamina quadrigemina. In conclusion, there is an association between MRI findings and elevated ICP in dogs; therefore, MRI might be useful to discriminate between dogs with and without elevated ICP.

T2-weighted magnetic resonance imaging measurements of optic nerve sheath diameter in dogs with and without presumed intracranial hypertension.

Intracranial hypertension is a cause of cerebral ischemia and neurologic deficits in dogs. Goals of this retrospective study were to test interobserver agreement for MRI measurements of optic nerve sheath diameter and associations between optic nerve sheath diameter, signalment data, and presumed intracranial hypertension status in a cohort of dogs. A veterinary radiologist interpreted scans of 100 dogs and dogs were assigned to groups based on presence or absence of at least two MRI characteristics of presumed intracranial hypertension. Two observers who were unaware of group status independently measured optic nerve diameter from transverse T2-weighted sequences. Mean optic nerve sheath diameter for all dogs was 3 mm (1-4 mm). The mean difference between observers was 0.3 mm (limits of agreement, -0.4 and 1.0 mm). There was no correlation between optic nerve sheath diameter and age for either observer (r = -0.06 to 0.00) but a moderate positive correlation was observed between optic nerve sheath diameter and body weight for both observers (r = 0.70-0.76). The 22 dogs with presumed intracranial hypertension weighed less than the 78 dogs without (P = 0.02) and were more often female (P = 0.04). Dogs with presumed intracranial hypertension had a larger ratio of optic nerve sheath diameter to body weight for each observer-side pair (P = 0.01-0.04) than dogs without. Findings indicated that the ratio of MRI optic nerve sheath diameter relative to body weight may be a repeatable predictor of intracranial hypertension in dogs.

A surgical technique for a terminal intracranial hypertension model in pigs.

The life-threatening effects of intracranial hypertension on brain perfusion and cerebral metabolism are the subject of current research in different animal models. The purpose of this study was to describe an efficient, reliable and inexpensive surgical method for temporary elevation of intracranial pressure (ICP) in acutely instrumented pigs in a research setting. Therefore, a balloon catheter was inserted into the left lateral ventricle and an ICP sensor was placed in the parenchyma of the right cerebral hemisphere. Ten acutely instrumented pigs were studied while under deep terminal general anaesthesia. The step-by-step inflation of the intraventricular balloon allows one to achieve the desired ICP up to 46 mmHg and maintain it at this level. ICP values ranged from a median of 2 (1-2) mmHg to 43 (29-45) mmHg. To the authors' knowledge, this is the first detailed description of a minimally invasive surgical technique for temporary ICP elevation in pigs via stepwise inflation of an intraventricular balloon.

Imaging diagnosis-transcranial color-coded duplex sonography in a dog with hepatic encephalopathy.

We report the use of transcranial Doppler ultrasonography in a dog with hepatic encephalopathy secondary to a congenital portosystemic shunt. A severe increase in the pulsatility index was measured in the right middle cerebral artery, left middle cerebral artery, and basilar artery. These values returned to normal following medical stabilization of the patient and resolution of the neurologic signs. Transcranial Doppler ultrasonography appears to have value for monitoring the status of intracranial hypertension in patients with hepatic encephalopathy.