Imaging diagnosis and clinical presentation of a Chiari malformation ...

Imaging diagnosis and clinical presentation of a Chiari malformation ...

s_bs_banner618 EQUINE VETERINARY EDUCATIONEquine vet. Educ. (2012) 24 (12) 618-623doi: 10.1111/j.2042-3292.2011.00359.xCase ReportImaging diagnosis and clinical presentation of a Chiarimalformation in a Thoroughbred foalA. Lempe*, M. Heine † , B. Bosch ‡ , K. Mueller § and W. BrehmLarge Animal Clinic for Surgery; † Large Animal Clinic for Theriogenology and Ambulatory Services;‡ Department of Small Animal Medicine; and § Institute of Pathology, University of Leipzig, Leipzig,Germany.Keywords: horse; Chiari malformation; spina bifida; congenital; MRISummaryA newborn Thoroughbred foal was presented to the clinicwith ambiguous neurological deficits, spinal anomalies anda soft tissue swelling dorsal to the lumbar vertebral column.The foal was alert but unable to rise and stand. Withradiography, ultrasonography, computed tomography(CT) and magnetic resonance imaging (MRI) a lumbardysraphic anomaly, cerebellar herniation and coincidentalskeletal abnormalities were documented. Finally, ameningomyelocele was defined and, in context with thecerebellar herniation through the foramen magnum, thefoal was diagnosed to have a Chiari malformation. The MRIexamination corresponded best with the post mortemfindings. Although 3-dimensional imaging methods havebeen considered superior regarding full and detailedassessment of the congenital malformation, radiographyand ultrasonography also provide essential information todiagnose dysraphic lesions at reduced costs and efforts. AChiari malformation should be considered as a differentialdiagnosis in foals with neurological deficits.IntroductionCleft anomalies and dysraphism are rare congenitalconditions in the equine species caused by an embryonicfailure of vertebral fusion (Copp and Greene 2010). Spinabifida is the most commonly used term describing suchmalformations. A more accurate definition refers to theextent of spinal cord protrusion through the cleft. In horsesmeningomyelocele and meningeal cysts of the cervicaland thoracic segment combined with dorsal or lessobvious ventral protrusion have already been described(Leathers et al. 1979; Harmelin et al. 1993; Doige 1996; Rivaset al. 1996; Jacobsen et al. 2007; Rendle et al. 2008;Gerhauser et al. 2010). Due to the variation of cleft*Corresponding author email: lempe@vetmed.uni-leipzig.deanomalies and other spinal deformities (Lerner and Riley1978; Kirberger and Gottschalk 1989; Ryan et al. 1992;Johnson et al. 1997; Wong et al. 2005) clinical signs areinconsistent including general paresis, ataxia, ‘dog-sitting’position and delayed or nonexistent response to reflextests. The majority of affected foals were diagnosed bynecropsy at only a few weeks or even months whenneurological signs had increased.A number of species, including calves (McFarland1959; Gruys 1973; Ohfuji 1999) sheep (Potter et al. 2010),dogs (Chesney 1973; Wilson et al. 1979; Ruberte et al.1995; Shamir et al. 2001) and cats (Plummer et al. 1993)can demonstrably develop spina bifida. However,the uncommon condition of a meningomyelocele inassociation with cerebellar herniation through the foramenmagnum has only been described in calves (Frauchigerand Fankhauser 1952; Gruys 1973; Cho and Leipold 1977;Madarame et al. 1993; LeClerc et al. 1997; Testoni et al.2010; Zani et al. 2010) and one dog (Schmidt et al. 2008).This complex congenital disorder has similarities withhuman Chiari malformation type II and, to date, nodescriptions exist referring to this condition in the equinespecies.The following report describes the first case of afoal with Chiari malformation using radiography,ultrasonography, MRI and CT in order to identify andto characterise the involved structures noninvasively.The imaging diagnosis which can be derived from suchtechniques was assessed and compared with the findingsof the post mortem examination.Case detailsHistoryA few hours old female Thoroughbred foal was referred tothe clinic for evaluation of a distinct swelling dorsal over thelumbar column and to clarify its inability to rise or stand. The© 2012 EVJ Ltd

A. Lempe et al. 621Fig 4: Sagittal (a) and transverse (b) MR-images of the lumbar region in T2-weighted spin echo sequence. Protrusion of the spinal cord isvisible (A) deviating from the enlarged epidural space (B). Nerve filaments of intermediate signal intensity ascend from the spinal cord(C; not visible on transverse images due to the greater slice thickness). The dorsal cavity is filled with hyperintense cerebrospinal fluid(D). Sagittal view of the cranium in a T2-weighted spin echo sequence (c). Cerebellar herniation through the foramen magnum is visible(2 arrows). Dilatation of the cranial spinal canal (hydromyelia) is marked by hyperintense signal intensity (arrowhead). Accuracy of theMR-interpretation was proved by the post mortem examination (a, c).Additionally, the lumbar vertebral column had a completedysraphic malformation dorsally from the 4th to 6thvertebrae (spina bifida aperta) with bullous protrusionof meninges and parts of the spinal cord(meningomyelocele). The cavity was filled with liquorspinalis (Fig 4a). After longitudinal sectioning of thecranium herniation of the cerebellar vermis through theforamen magnum was obvious and therefore the imagingdiagnosis of a Chiari malformation type II could beconfirmed (Fig 4c).DiscussionSpina bifida is classified as spina bifida aperta (also cystica)defined by a protrusion of spinal tissue through the cleftvertebrae or as spina bifida occulta where the spinal cordtissue remains in place. Depending on the protrudingtissue, a spina bifida aperta can be divided into 3 subtypes.In case of a meningocele only the meninges bulge out toform an apparent cyst (Leathers et al. 1979; Doige 1996)whereas a meningomyelocele is characterised by thepassage of meninges and parts of the spinal tissueincluding nerve cords through the bone cleft (Harmelinet al. 1993; Rivas et al. 1996; Jacobsen et al. 2007). Inhuman medicine this type is the most common amongall spinal defects (DeMarco et al. 2011). Myeloschisisrepresents the most severe subtype by exposing spinaltissue without a covering of skin, and to date this conditionhas not been reported in horses.A previous report of a miniature colt with a cervicalmeningomyelocele and hydrocephalus has alreadysuggested a Chiari malformation, but there was no provenevidence because of the lack of diagnostic imaging ofthe head and necropsy (Rivas et al. 1996). In our case,MR examination allowed the determining depictionof cerebellar herniation to diagnose a Chiari-like© 2012 EVJ Ltd

622 Chiari malformation in a foalmalformation noninvasively. Even though the finaldiagnosis was based on MR findings of a foal recentlysubjected to euthanasia, such an examination is alsopractical in foals under general anaesthesia.The associated meningomyelocele was protrudingdorsal from the lumbar vertebrae, easily assessable withother imaging modalities. Radiographic indication ofspina bifida in the presented case was the appearanceof nonfused spinous processes in conjunction with aradiopaque mass dorsal to the suspected cleft. If possible,a ventrodorsal or dorsoventral orientation is preferable inyoung foals as in laterolateral views both parts of thespinous process superimpose. However, additionalcomplex malformation of the spinal column can also leadto superimposition of the dysraphic segment. Contrastmyelography may have resulted in increased informativevalue but due to the oncoming diagnostic procedures itwas not performed. Regarding the classification of thedysraphic lesion, ultrasonography was useful to evaluatesoft tissue involvement and furthermore to exclude othercauses of swellings along the column such as haematoma,seroma, neoplasia or vertebral fractures. In comparison tothe post mortem findings this method is considered to bemore sensitive than radiography. One report documentedthe cerebellar displacement in a calf ultrasonographicallyat the craniocervical junction but due to the differentequine anatomy the approach through the foramenmagnum is impractical in horses (Testoni et al. 2010). Threedimensionalimaging techniques are advantageous forvisualising complex vertebral malformations. Both, CTand MRI provided specific information and were equallyimportant to describe the multiple malformations of thiscase in detail. Computed tomography revealed thedegree of vertebral anomaly, the extension of the scoliosisin connection with vertebral rotation and the abnormalfusion of 3 ribs, findings which were incompletelydocumented during radiography. Most likely the fractureof the left 18th rib originates from parturition or a post natalevent. The conclusive diagnosis was based on MR-images.This imaging technique depicted the lumbar dysraphiclesion in close agreement with the pathological findings byshowing the exact protrusion of spinal cord tissue andmeninges, ascending nerve filaments, bulging tissue ofthe epidural space and accumulation of cerebrospinalfluid. T2-weighted sequences provided best detail. Thecombination of a spina bifida with other skeletalabnormalities is a previously described phenomenon (Choand Leipold 1977; Madarame et al. 1993; Ruberte et al.1995; Doige 1996; Denoix 2005; Jacobsen et al. 2007;Gerhauser et al. 2010). Thus it is advisable to preciselyevaluate a neonate or yearling with skeletal deformityand/or neurological signs as there is a wide range ofdifferential neurological diseases in young horses (MacKay2005; Johnson 2010); eventually the prognosis deteriorateswhen spina bifida has been diagnosed. In dogs, attemptsto correct spina bifida surgically are described (Fingerothet al. 1989; Shamir et al. 2001) but in horses no suchinterventions have been documented as being successful(Rivas et al. 1996). For the equine species an appropriatesurgical technique to treat cerebellar herniation is currentlynot available. The MR examination is regarded as essentialto distinguish foals with a fatal Chiari-like malformation fromthose only with vertebral abnormalities and to diagnoseless obvious dysraphism such as spina bifida occulta, ameningocele, ventral or cervical meningomyelocele intravitam.The occurrence of spina bifida in man is closelyassociated with folic acid deficiency but geneticdistribution, maternal age and diet also play a role (Coppand Greene 2010; DeMarco et al. 2011). The influence ofretinoic acid excess and a zinc deficiency may also leadto an increased prevalence of congenital dysraphism(Yasuda et al. 1986; Dubrulle and Pourquie 2004; Rendleet al. 2008). Oral supplementation of the B-vitaminfolic acid reduces the incidence of spina bifida in manbut a primary folate deficiency in horses is virtuallyimpossible considering their natural diet. However, itcould be demonstrated that secondary folate deficiencyappeared in horses after administrating sulphadiazineand pyrimethamine to treat equine protozoalmyeloencephalitis (Toribio et al. 1998; Piercy et al. 2002).Unfortunately we could not receive any informationregarding possible medical treatment during gestation ofthe mare in our case. In general, the mare and her foalwere in good body condition; none of the earlier foals ofthe mare had shown signs of a developmental disease. Abreed disposition can not be derived from literature.In conclusion, a Chiari malformation is a congenitaldisease also occurring in the equine species, the prognosisof which deteriorates when diagnosed. MRI is an importantdiagnostic modality to distinguish foals with this fataldisease from those with neurological disorders for otherreasons. Although 3-dimensional imaging methods weresuperior to assess the dysraphic anomaly in detail,conventional radiography and ultrasonography wereinexpensive alternatives that have proven to be sufficientlyconclusive in practice.Authors’ declaration of interestsNo conflicts of interest have been declared.Manufacturers’ addresses1 Fuji Photo Film GmbH, Düsseldorf, Germany.2 GE Healthcare Technologies, Solingen, Germany.3 Philips Healthcare, Hamburg, Germany.ReferencesChesney, C.J. (1973) A case of spina bifida in a Chihuahua. Vet. Rec. 93,120-121.Cho, D.Y. and Leipold, H.W. (1977) Arnold-Chiari malformation andassociated anomalies in calves. Acta Neuropathol. (Berl.) 39,129-133.© 2012 EVJ Ltd

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(2010) Imagingdiagnosis – split cord malformation. Vet. Radiol. Ultrasound 51, 57-66.Supporting informationAdditional supporting information may be found in the online version ofthis article.Fig S1: Photograph of a Thoroughbred foal a few hours old showing adistinct swelling at the dorsal lumbar region. There is also a scolioticmalformation of the thoracolumbar vertebral column visible.Please note: Wiley-Blackwell are not responsible for the content orfunctionality of any supporting materials supplied by the authors. Anyqueries (other than missing material) should be directed to thecorresponding author for the article.© 2012 EVJ Ltd

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