a case of acquired acute obstructive hydrocephalus that developed as a complication of an ischaemic infarct in the vascular territory of the rostral cerebellar artery is described in an adult domestic shorthair cat . this is the first report of obstructive hydrocephalus as a complication of an ischaemic infarct in the region of the rostral cerebellar artery in a cat . mri findings are described in detail with regard to the recognition of the early signs of obstructive hydrocephalus . a brief review of the literature a 7-year-5-month - old neutered female domestic shorthair cat was referred to our neurological department with a history of acute non - ambulatory tetraparesis for a duration of 20 h. prior to the onset of clinical signs , the cat was healthy , regularly vaccinated and dewormed . during the time between the onset of clinical signs and hospital admission , a pathological horizontal positional nystagmus with slow phase in the left direction was noted when changing the head posture of the cat . examination revealed non - ambulatory tetraparesis ( worse on the right side ) with conscious proprioception absent in the right thoracic and pelvic limbs and delayed in the left thoracic and pelvic limbs . on the basis of the neurological examination findings , the cat was suspected to have a right - sided paradoxal vestibular syndrome with involvement of the right cerebellum ( caudal cerebellar peduncle , flocculonodular lobe and fastigial nucleus ) , right pons and medulla oblongata . a vascular accident was considered most likely because of the abrupt onset of the clinical signs without pain during examination . however , other potential causes included traumatic , neoplastic , infectious / inflammatory disease of the central nervous system . an mri study using a 1.5 t scanner ( hallmarq petvet companion animal mri ) was performed the same day . buthorphanol 0.2 mg / kg ( torbugesic 10 mg / ml ; zoetis ) was given intravenously as a sedative agent . midazolam 0.1 mg / kg ( hypnovel ; roche ) in association with propofol 4 mg / kg ( propoflo plus ; zoetis ) were administered intravenously during general anaesthetic induction . a single dose of lidocaine ( xylocaine 10% spray ; apen pharma trading ) was sprayed locally at the level of the glottis to avoid coughing during intubation . a 5 mm uncuffed endotracheal tube ( portex ; smith medicals ) was positioned endotracheally to maintain general anaesthetic with 2.5% sevoflurane ( sevoflurane ; abbvie ) inhalational anaesthetic gas in oxygen . hartmann s crystalloid ( vetivex 11 ; dechra veterinary products ) at variable dose of 210 ml / kg was administered as a continuous infusion during the anaesthetic procedure and hospitalisation time . vital parameter monitoring during general anaesthesia was obtained via magnitude 31 mri compatible monitoring ( magnitude 3150 m ; invivo , philips healthcare ) and included electrocardiogram , pulse oximetry , capnography ( co2 ) in the respiratory gases , oscillometric blood pressures and respiration rates . the following sequences with a slice thickness of 3 mm were acquired : t2-weighted ( t2w ) fast spin echo ( fse ) images in the sagittal ( tr 2522 , te 110 ) transverse ( tr 3298 , te 110 ) and dorsal ( tr 2522 , te 110 ) planes ; t2w fluid - attenuated inversion recovery ( flair ) ( tr 7105 , te 100 ) in the transverse plane ; t2*w gradient echo ( tr 646 , te 17 ) in the transverse plane ; and t1-weighted ( t1w ) fse images in the sagittal ( tr 400 , te 17 ) and transverse ( tr 493 , te 17 ) planes before and after intravenous ( iv ) gadolinium administration ( 0.5 mmol / ml gadopentetate dimeglumine [ magnevist ; bayer pharma ] ) . a single , focal cerebellar lesion that was isointense to grey matter on t1w images , hyperintense on t2w and t2w flair images and on t2*w gadolinium - enhanced images , with no contrast uptake after iv contrast medium administration , was noted in the right rostral aspect of the cerebellum . on sagittal midline images , the lesion involved the rostral cerebellum ( figure 1 ) . on transverse images , the lesion was shown to be affecting the right cerebellum and had an upturned wedge - shaped appearance , radiating outwards dorsally and extending to the dorsal surface of the cerebellum and ventrally towards the fourth ventricle ( figure 2 ) . mri of the brain demonstrating the suspected cerebellar infarct ( * ) : ( a ) sagittal ; ( b ) transverse ; and ( c ) dorsal t2-weighted images . note the hyperintense wedge - shaped lesion visible in the right rostral cerebellum radiating dorsally towards the dorsal surface of the cerebellum and ventrally towards the fourth ventricle ( * ) ( a ) t2-weighted ; ( b ) fluid - attenuated inversion recovery ( flair ) ; and ( c ) t1-weighted transverse images of the brain at the level of the rostral cerebellum . note the t2 and flair hyperintensity compared with the grey matter and the t1 hypointense wedge - shaped lesion radiating ventrally towards the fourth ventricle ( black arrow ) the ventricular system was asymmetrically enlarged , and dilatation of the right olfactory recess could be clearly appreciated in both transverse and dorsal t2w images ( figure 3 ) . mri of the brain : ( a ) midsagittal t2-weighted image ; ( b ) t2-weighted transverse section at the level of the interthalamic adhesion ; and ( c ) t2-weighted dorsal section at the level of the olfactory aperture . ( a ) note the interthalamic adhesion that has lost its distinctly circular shape ( white arrow ) , the corpus callosum that is significantly elevated ( black arrow ) and the overcrowding of the caudal  cranial fossa without cerebellar herniation ( black arrow point ) . ( b ) note the flattening of interthalamic adhesion ( black arrow ) , the diminished suprasellar cistern secondary to the third ventricle expansion ( + ) and the narrowing of cerebral sulci , as well as the obliteration of the subarachnoid space around the dorsal convexity of the cerebral hemisphere . ( c ) note the dilatation of the right olfactory recess ( white arrow ) on the transverse t2w image at the level of the interthalamic adhesion , it was possible to observe flattening of the interthalamic adhesion and a diminished suprasellar cistern secondary to the third ventricle expansion . a narrowing of the cerebral sulci and obliteration of the subarachnoid space around the dorsal convexity of the cerebral hemispheres was also evident ( figure 3 ) . on the midsagittal t2w image , it was possible to observe a deformation of the interthalamic adhesion with loss of its distinctly circular shape and a significant elevation of the corpus callosum . overcrowding of the caudal cranial fossa without cerebellar herniation was also present ( figure 3 ) . considering the changes observed on the mri study , a hyper - acute territorial ischaemic infarction in the vascular territory of the right rostral cerebellar artery ( rca ) with acquired acute obstructive hydrocephalus was suspected . because the morphological changes observed upon mri were indicative of increased intracranial pressure ( icp ) , cerebrospinal fluid collection was not performed . given the mri findings , the most likely predisposing factors that could have resulted in the rostral cerebellar artery ischaemic infarct were considered and investigated . these factors included septic thromboembolism associated with bacterial endocarditis or other infectious diseases ; aortic and cardiac thromboembolism secondary to cardiovascular disease or hyperthyroidism ; embolic metastatic tumour , intravascular lymphoma , or fibrocartilaginous thromboembolism ; and , although less likely because of the geographic location , parasite migration ( eg , cuterebra species larvae ) or parasitic emboli ( eg , dirofilaria species ) . prothrombin time , activated partial thromboplastin time , thyroxine level , electrocardiogram , echocardiogram and radiographs of the thorax ( three projections ) and abdomen ( two projections ) were within normal limits . multiple systolic blood pressure measurements were obtained using doppler and were found to be between 150 and 190 mmhg . ua findings consistent with urinary tract infection and enterococcus species identified on urine culture were sensitive to potentiated amoxicillin . because cerebrospinal fluid was not collected owing to suspected increased icp and associated elevated risk of complication , blood samples were obtained for an elisa to identify the feline leukaemia virus p27 antigen and feline immunodeficiency virus antibody . the results of the elisa were negative , and serology tests to investigate antibody titres for toxoplasma and coronavirus were within normal limits . because an underlying cause of the suspected ischaemic infarct was not found and because the mri findings indicated increased icp , the cat remained hospitalised . before and after the mri the cat appeared stable clinically and treatment directed at reducing icp was not considered necessary . the cat remained on continuous iv administration of crystalloid ( hartmann s [ vetivex 11 ; dechra veterinary products ] ) at a dose of 4 ml / kg / h and on iv administration of potentiated amoxicillin ( augmentin beecham group ) at a dose of 20 mg / kg q12h . the level of consciousness , heart rate and respiratory rate were monitored hourly , and the body temperature and blood pressure were monitored every 6 h. the following day , 46 h after the initial presentation of the clinical signs , the cat showed peracute deterioration . the cat s responsiveness suddenly declined , and the cat was found unconscious in lateral recumbency with bilateral mydriasis , absent pupillary light reflexes ( plrs ) and respiratory arrest . prompt tracheal intubation , 100% oxygen administration with manual ventilation , initial hyperventilation , iv administration of 0.3 mg / kg dexamethasone disodium phosphate ( colvasone 2 mg / ml ; norbrook laboratories ) and 1 g / kg mannitol 10% solution ( polyfusor ; fresenius kabi ) improved the neurological status of the cat . however , mentation remained severely depressed , whereas the pupil size and plr improved 20 mins after mannitol administration . further deterioration in the neurological signs occurred within the next few hours , including seizures , bilateral mydriasis with absent plr , cardiac dysrhythmias and respiratory arrest . because of the grave prognosis the owner consented to euthanasia . ischaemic infarcts affecting the territory of the rca are clinically described as resulting in peracute , non - progressive signs of neurological deficits characterised by ataxia with or without hypermetria , non - ambulatory paresis , head tilt , nystagmus , ventrolateral strabismus , decreased menace response , postural and proprioceptive deficits . these infarcts are the result of severe hypoperfusion of the rostral cerebellum and medulla because of an obstruction caused by a thrombus originating within the rca or from an embolus migrating from elsewhere in the body . the rca in cats and dogs arises from the arterial circle and vascularises the rostral cerebellum , with collateral branches directed to the medulla and pons . ischaemia results in energy deprivation , leading to the development of anaerobic glycolysis , lactic acidosis , inflammation , free radical formation , capillary endothelial damage and blood  brain barrier ( bbb ) disruption . the first phase is characterised by an intracellular accumulation of water due to failure of the ionic pumps ( cytotoxic oedema ) , which develops a few minutes after the event . a second phase is characterised by the leakage of water and proteins into the extracellular space from the damaged bbb ( vasogenic oedema ) , which has been reported to develop within a few hours ( 46 h ) and can last for 35 days . in these cases , the infarcted parenchyma and the surrounding vasogenic oedema behave like a space - occupying mass in the caudal fossa , causing brainstem compression , collapse of the fourth ventricle and an obstructive hydrocephalus . in the small animal literature , this complication has been suspected but never documented . the mri changes reported in this case report are similar to previously reported cerebellar infarcts in the small animal literature . the abnormality on mri was confined to the specific territory supplied by the rca , had a sharp demarcation from the surrounding parenchyma , a distribution predominantly in the grey matter and an angular ( wedge ) shape ( figure 1 ) . the presumed infarcted area presented with increased t1 and t2 prolongation time that resulted in low signal intensity ( compared with the surrounding parenchyma ) in t1w images and high signal intensity in t2w and t2 flair images ( figure 2 ) . it was possible to appreciate in t2w and flair images a moderate mass effect of the presumed infarcted area on the surrounding brain parenchyma . in t1w post - contrast images it was also possible to appreciate a lack of contrast enhancement probably secondary to the poor vascularisation present in the presumed infarcted area as described in similar cases . mri findings were consistent with acute obstructive hydrocephalus as described previously , and included the dilatation of the right olfactory recess , flattening of the interthalamic adhesion and diminished suprasellar cistern secondary to the third ventricle expansion , and deformation of the interthalamic adhesion that was not distinctly circular in the midsagittal plane . additionally , there was a narrowing of the cerebral sulci , obliteration of the subarachnoid space around the dorsal convexity of the cerebral hemisphere , elevation of the corpus callosum and overcrowding of the caudal fossa ( figure 3 ) . because of the peracute obstruction at the level of the fourth ventricle , the pressure in the ventricle would increase quickly and cause ventriculomegaly . the narrowing of the cerebral sulci and the obliteration of the subarachnoid space , seen in the mri , are most likely the result of the high pressure in the ventricle and the low pressure in the arachnoid space . overcrowding of the caudal fossa is reported to be associated with increased icp in hydrocephalic patients . however , there is also the possibility that the overcrowding is simply an incidental finding that is often encountered in domestic shorthair cats . in humans , treatment of obstructive hydrocephalus as a complication of cerebellar infarct is aimed at reducing the increased pressure secondary to the accumulation cerebrospinal fluid . standard measures include hyperventilation , osmotic diuretics or decompressive surgery in the most severe cases , where coma and cardiorespiratory difficulties occur . despite intensive medical management , mortality is estimated to be as high as 5070% , and surgical decompressive treatment is performed as an extreme attempt to stabilise these patients . treatment to reduce the increased icp in this case was performed only when the cat showed acute neurological deterioration , and it was not successful . mannitol or hypertonic saline solution was not administered immediately after the mri to prevent any possible leakage through the damaged bbb , which , theoretically , could have led to a further increase in the icp . however , a review of the literature suggested that all osmotic agents have a limited period of effectiveness and multiple administrations may have significant metabolic effects without additional effectiveness in reducing icp . although glucocorticoids are reported to be very useful in the treatment of vasogenic oedema due to neoplastic or inflammatory conditions , they are reported to be not helpful in the treatment of cytotoxic oedema and can cause deterioration in patients suffering from ischaemic lesions . these drugs were used instead when the cat acutely deteriorated in an attempt to control the vasogenic oedema that was causing the neurological deterioration , to reduce csf production and therefore icp . while this is only speculation , prompt action focused on medically reducing icp with administration of mannitol and steroids may have helped attain a better outcome . a limitation of this study was the lack of histopathology s confirmation of the cause of the cerebellar lesion in this case with studies previously published in small animal literature that have demonstrated the difficulties of differentiating ischaemic stroke from neoplastic ( gliomas ) and inflammatory diseases in mri . however , together the anamnesis and clinical findings combined with the mri findings support the diagnosis and likely the cause of the cat s deterioration . this is the first case report describing suspected hypertensive hydrocephalus developing as a complication of a territorial ischaemic infarct affecting the rca . awareness of this potential complication and prompt recognition of the associated clinical signs may help clinicians in their monitoring and medical management of cats presenting with suspected cerebellar infarction .
case summarya case of acquired acute obstructive hydrocephalus that developed as a complication of an ischaemic infarct in the vascular territory of the rostral cerebellar artery is described in an adult domestic shorthair cat . 
 the clinical findings , diagnostic investigations , treatment and prognosis are reported . 
 mri findings are described in detail.relevance and novel informationthis is the first report of obstructive hydrocephalus as a complication of an ischaemic infarct in the region of the rostral cerebellar artery in a cat . 
 mri findings are described in detail with regard to the recognition of the early signs of obstructive hydrocephalus . a brief review of the literature 
 is included , as this complication has been frequently reported in humans .