Filipiddis

Fingeroth

Fletcher

Hertzler

Lahunta

Michelson

Nakanishi

Ogiwara

Ostling

Plummer

Ricci

Shamir

Steinbok

Vernet

Yamada

Yong

Zani

English

PubMed

S. De Decker

T. Gregori

P.J. Kenny

C. Hoy

K. Erles

H.A. Volk

Crossref

Journal of Veterinary Internal Medicine

Tethered Cord Syndrome Associated with a Thickened Filum Terminale in a Dog

De Decker, S

Gregori, T

Kenny, P J

Hoy, C

Erles, K

Volk, H A

RVC Research Online

Tethered Cord Syndrome Associated with a Thickened FilumTerminale in a DogS. De Decker, T. Gregori, P.J. Kenny, C. Hoy, K. Erles, and H.A. VolkKey words: Cauda equina; Lumbosacral; Spinal dysraphism; Spinal malformation.A1-year-old female neutered English Cocker Spanielwas presented with a 9 months history of progres-sive right pelvic limb lameness. Survey radiographs,computed tomography (CT), magnetic resonance imag-ing (MRI), and joint taps of the pelvis, stifles, hockjoints and tarsi, performed before referral, were withinnormal limits. Medical management with meloxicamdid not result in clinical improvement. Treatment withgabapentin, initiated 7 days before presentation,resulted in improvement. General physical examinationdid not reveal any abnormalities. Neurological examina-tion revealed paraparesis, right pelvic limb lameness, alow tail carriage, proprioceptive deficits expressed bydelayed hopping, but intact paw placement in both pel-vic limbs, a reduced withdrawal reflex in the right pelviclimb and decreased tail tone. Pain was elicited on lum-bosacral palpation, dorsal extension of the tail andextension of both hips. The remainder of the neurologi-cal examination was within normal limits. Her neuro-logical lesion was localized to the L4-S3 spinal cordsegments. A complete blood count and biochemistrypanel were within normal limits. After premedicationwith methadone (0.2 mg/kg IM) and acepromazine(0.0 1mg/kg IM), anesthesia was induced with propofol(4–6 mg/kg, IV), and maintained with sevoflurane inoxygen. MRIa of the lumbar and lumbosacral vertebralcolumn was performed with the dog in dorsal recum-bency with flexed limbs (ie, frog-leg position). Theimaging protocol included sagittal and transverse planeT2-weighted (repetition time (ms) (TR), echo time (ms)(TE), 3000/120), sagittal and dorsal plane T2-weightedshort-tau inversion recovery (TR/TE, 3612/80), andtransverse plane T2-weighted BAL TGRAD (TR/TE,7.9/3.9) sequences. Sagittal and transverse planeT1-weighted (T1W TSE) (TR/TE, 400/8) images wereacquired before and after IV injection with gadoliniumcontrast.b MRI demonstrated possible caudodorsal dis-placement of the conus medullaris. Mild lumbosacralintervertebral disk protrusion was also seen (Fig 1).After MRI, a CT examination of the lumbosacral verte-bral column was performed using a 16-slice scanner.cAfter completion of the transverse CT study, sagittaland dorsal reconstructions were made. CT imaging(Fig 2) confirmed the MRI findings and did not revealany other vertebral or spinal abnormalities. Differentialdiagnoses included tethered cord syndrome anddynamic lumbosacral vertebral canal stenosis. Givenher initial positive response, medical management wascontinued with gabapentin (10mg/kg, q8h, PO), carpro-fen (2mg/kg, q12h, PO) and restricted exercise for4 weeks. A re-examination 4 weeks later demonstratedprogression of her clinical signs characterized by morepronounced paraparesis and right pelvic limb lameness.General anesthesia was induced and maintained withthe aforementioned protocol. A standard dorsal lumbo-sacral laminectomy, from L7 to S2 was performed.After opening the vertebral canal, a ligamentous struc-ture was identified between the conus medullaris andthe dorsal lamina of S2, which caused caudodorsaldisplacement and traction of the conus medullaris(Fig 3A,B). After sectioning and sampling the distalaspect of this ligamentous structure, the conusmedullaris regained a more cranial position. The woundwas closed routinely. Intraoperative analgesia wasprovided with ketamine (loading dose of 0.5 mg/kg IVfollowed by a CRI at 10 lg/kg/min IV) and methadone(0.1 mg/kg q4h, IV). Postoperative analgesia consistedof a combination of methadone (0.2 mg/kg, q4h, IV),carprofen (2 mg/kg, q12h, PO) and gabapentin(10 mg/kg, q8h, PO). The dog was discharged fromhospitalization 4 days after surgery. The owner wasadvised to provide strict rest for 4 weeks in combina-tion with gabapentin and carprofen for 2 more weeks.From the Department of Veterinary Clinical Science and Services,(De Decker, Gregori, Kenny, Hoy, Volk); Department of Pathologyand Pathogen Biology, The Royal Veterinary College, University ofLondon, North Mymms, Hertfordshire England (Erles).Department of Veterinary Clinical Science and Services, TheRoyal Veterinary College, University of London, Hawkshead Lane,North Mymms, Hertfordshire AL97TA, England.This case report was presented in abstract form (poster) at the27th Symposium of the European College of Veterinary Neurology(ECVN), 18–20 September 2014, Madrid, Spain.Corresponding author: S. De Decker, Department of VeterinaryClinical Science and Services, The Royal Veterinary College, Uni-versity of London, Hawkshead Lane, North Mymms, HertfordshireAL97TA, England; e-mail: sdedecker@rvc.ac.uk.Submitted September 15, 2014; Revised October 28, 2014;Accepted November 11, 2014.Copyright © 2015 The Authors. Journal of Veterinary InternalMedicine published by Wiley Periodicals, Inc. on behalf of AmericanCollege of Veterinary Internal Medicine.This is an open access article under the terms of the CreativeCommons Attribution-NonCommercial License, which permits use,distribution and reproduction in any medium, provided the originalwork is properly cited and is not used for commercial purposes.DOI: 10.1111/jvim.12522Abbreviations:CT computed tomographyMRI magnetic resonance imagingTCS tethered cord syndromeCase ReportJ Vet Intern Med 2015;29:405–409Histopathological evaluation revealed a combination ofelastin and collagen fibers in parallel arrangement, con-firming the ligamentous nature of the sampled tissue(Fig 3C). The surgical- and histopathological findingswere considered diagnostic for tethered cord syndromeassociated with a thickened and shortened filumterminale. A neurological examination 4 weeks after sur-gery revealed marked clinical improvement. At this time,the dog demonstrated mild lameness and proprioceptivedeficits in the right pelvic limb. A neurological examina-tion 10 weeks after surgery did not reveal any abnormali-ties. A telephone interview with the owner and referringA BC DFig 1. T2-weighted sagittal image of the lumbosacral region (A) and transverse BAL TGRAD image at the level of L7-S1 (B) demonstrat-ing possible caudodorsal displacement of the conus medullaris. (A) The conus medullaris extends until the cranial aspect of L7. (B) Thedural sac is located dorsally against the lamina of S1. T2-weighted sagittal image of the lumbosacral region (C) and transverse BALTGRAD image at the level of L7-S1 (D) in a 1.5-year-old male English Cocker Spaniel without a spinal problem. (C) The conus medullaristerminates at the cranial aspect of L6. (D) The dural sac lies on the floor of the vertebral canal.A BC DFig 2. Transverse CT image at the level of the lumbosacral joint (A) and a sagittal reconstructed CT image (B) demonstrating possiblecaudodorsal displacement of the conus medullaris. Hypodense signal suggestive of epidural fat can be seen ventral from the conus medul-laris (arrow). Transverse CT image (C) at the level of the lumbosacral joint and a sagittal reconstructed CT image (D) of a neurologicallynormal 1-year-old male English Cocker Spaniel for comparison.406 Decker et alveterinary surgeon 8 months after surgery revealed thatthe dog was free of clinical signs.Tethered cord syndrome (TCS) represents a spec-trum of congenital anomalies characterized by anabnormal caudal position and traction of the conusmedullaris.1,2 It can be associated with a variety ofspinal malformations, including fatty infiltration of thefilum terminale and open and closed forms of spinaldysraphism.3 TCS can, however, also be associatedwith an abnormally thickened, inelastic, and shortenedfilum terminale without other spinal or vertebralmalformations.3 In people, this is also referred to astrue or primary TCS.1,4 In the case presented here, noother spinal or vertebral malformations were presentand caudal traction of the conus medullaris was mostlikely caused by an abnormally thickened, inelastic,and shortened filum terminale. Although reported inconjunction with an intradural lipoma, myelomeningo-cele, spina bifida, myeloschisis, and a split cordmalformation5–9, this case report, to the best of theauthors’ knowledge, represents the first veteri-nary report of TCS associated with a thickened filumA BCFig 3. (A, B) Intraoperative pictures demonstrating caudal traction of the conus medullaris associated with a thickened filum terminale(arrow). Other intraoperative abnormalities included moderate hypertrophy of the ligamentum flavum (asterisk). (C) Histopathologicalevaluation (HE staining) demonstrated a combination of elastin and collagen fibers in parallel arrangement. 9 40 Bar: 0.5 mm.Tethered Cord Syndrome 407terminale. The conus medullaris is the tapered endingof the spinal cord and is continued by a filament, thefilum terminale. The filum terminale extends caudallyand attaches to a sacral or caudal vertebra.10 Thicken-ing of the filum terminale and subsequent TCS resultsfrom abnormal embryological development of thefilum terminale during the process of retrogressive dif-ferentiation.2 The process of neurulation is not respon-sible for formation of the entire spinal cord. Distal tothe caudal neuropore, undifferentiated cells form thecaudal cell mass. This structure will proliferate, cana-lize, fuse with the neural tube and will eventuallydevelop into the conus medullaris, cauda equina, andfilum terminale. The filum terminale forms throughregression of the most caudal portion of the caudalcell mass during a process called retrogressive differen-tiation. A thickened filum terminale may result fromincomplete involution of the caudal cell mass.2,3,11 Thethickened and shortened filum terminale causes progres-sive and repeated traction on the conus medullaris andcaudal spinal cord segments. This results in decreasedblood flow and decreased oxidative metabolism of thespinal cord segments just cranial of the inelastic abnor-mality.1,12 TCS therefore typically results in progressivedysfunction of the lumbosacral spinal cord segments.1,2The degree and reversibility of this dysfunction dependson both the magnitude and duration of the excessive trac-tion.13 In the case reported here, reaching a diagnosis ofTCS proved to be very challenging. Interpretation ofadvanced imaging was subjective and unfortunatelyinconclusive. A diagnosis of TCS was only confirmedduring surgery. In people with TCS, MRI is consideredthe imaging modality of choice and abnormalities typi-cally include a thickening of the filum terminale and anelongated conus medullaris in an abnormally caudodor-sal position.1–3 This radiological definition is difficult touse in dogs, because there is considerable variability intermination of the conus medullaris14 and filum termi-nale.10 Furthermore, no specific data are available onnormal MRI or CT characteristics of the canine filumterminale. A proportion of people with primary TCSpresent with the conus medullaris in a normal position.This is referred to as occult TCS.15,16 Considering thesearguments, it cannot be excluded the dog described herepresented with occult TCS instead of TCS with an abnor-mal caudodorsal position of the conus medullaris. Per-forming MRI in different body positions has beenevaluated to facilitate diagnosing occult TCS in people.Decreased spinal cord motion between the prone andsupine position has been considered suggestive forTCS.15,17 The dog presented here, recovered completelyafter surgical transection of the filum terminale. Becauseuntreated TCS will lead to progressive deterioration ofneurological function, surgical untethering is consideredthe treatment of choice in people.1,16 The goal of surgeryis to remove abnormal tension on the spinal cord withoutcausing further trauma.1 In contrast to TCS associatedwith more complex vertebral malformations, such asspina bifida, transection of a thickened filum terminale isconsidered a technically straightforward procedure asso-ciated with a low postoperative morbidity and goodprognosis for recovery. Rethetering with recurrence ofclinical signs, caused by arachnoid adhesions, has beenreported in a small proportion of surgically treatedcases.16–20In summary, this report described TCS associatedwith a thickened filum terminale in a dog. Reaching adiagnosis was challenging and surgery resulted in com-plete clinical recovery. TCS associated with a thickenedfilum terminale could be considered a rare differentialdiagnosis for lumbosacral neurological dysfunction in ayoung dog.Footnotesa 1.5 tesla Intera, Philips Medical System, Eindhoven, the Nether-landsb 0.1 mL/kg gadoterate meglumine, Dotarem, Guerbet, MiltonKeynes, Englandc PQ 500, Universal Systems, Solon, OHAcknowledgmentsFunding: No funding was received for this study.Conflict of Interest Declaration: Authors disclose noconflict of interest.Off-label Antimicrobial Declaration: Authors declareno off-label use of antimicrobials.References1. Lew SM, Kothbauer KF. Tethered cord syndrome: Anupdated review. Pediatr Neurosurg 2007;43:236–248.2. Hertzler DA, Depowell JJ, Stevenson CB, et al. Tetheredcord syndrome: A review of the literature from embryology toadult presentation. Neurosurg Focus 2010;29:E1. doi:103171/20103Focus1079.3. Michelson DJ, Ashwal S. Tethered cord syndrome in child-hood: Diagnostic features and relationship to congenital anoma-lies. Neurol Res 2004;26:745–753.4. Yamada S, Won DJ. What is the true tethered cord syn-drome? Childs Nerv Syst 2007;23:371–375.5. Fingeroth JM, Johnson GC, Burt JK, et al. Neuroradio-graphic diagnosis and surgical repair of tethered cord syndrome inan English bulldog with spina bifida and myeloschisis. J Am VetMed Assoc 1989;194:1300–1302.6. Plummer SB, Bunch SE, Khoo LH, et al. Tethered spinalcord and intradural lipoma associated with a meningocele in aManx-type cat. J Am Vet Med Assoc 1993;203:1159–1161.7. Shamir M, Rochkind S, Johnston D. Surgical treatment oftethered spinal cord syndrome in a dog with myelomeningocele.Vet Rec 2001;148:755–756.8. Zani DD, De Zani D, Morandi N, et al. Imagingdiagnosis—Split cord malformation. Vet Radiol Ultrasound2010;51:57–60.9. Ricci E, Cherubini GB, Jakovljevic S, et al. MRI findings,surgical treatment and follow-up of a myelomeningocele with teth-ered spinal cord syndrome in a cat. J Feline Med Surg2011;13:467–472.10. Fletcher TF. Spinal cord and meninges. In: Evans HE andde Lahunta A, ed. Miller’s Anatomy of the Dog, 4th ed.St Louis, Missouri: Elsevier Saunders; 2013: 589–610.408 Decker et al11. Yamada S, Zinke DE, Sanders D. Pathophysiology of“tethered cord syndrome”. J Neurosurg 1981;54:494–503.12. Filipiddis AS, Kalani Y, Theodore N, et al. Spinal cordtraction, vascular compromise, hypoxia, and metabolic derange-ments in the pathophysiology of tethered cord syndrome. Neuro-surg Focus 2010;29:E1. doi:103171/20103Focus1085.13. Yamada S, Iacono RP, Andrade T, et al. Pathophysiologyof tethered cord syndrome. Neurosurg Clin N Am 1995;6:311–323.14. De Lahunta A, Glass E. Lower motor neuron: Spinalnerve, general somatic efferent system. In: de Lahunta A andGlass E, ed. Veterinary Neuroanatomy and Clinical Neurology,3rd ed. St Louis, Missouri: Elsevier Saunders; 2009:77–133.15. Nakanishi K, Tanaka N, Kamei N, et al. Use of proneposition magnetic resonance imaging for detecting the terminalfilum in patients with occult tethered cord syndrome. J NeurosurgSpine 2013;18:76–84.16. Steinbok P, MacNeily AE. Section of the terminal filum foroccult tethered cord syndrome: Toward a scientific answer.Neurosurg Focus 2007;23:E5. doi: 10.3171/FOC-07/08/E5.17. Vernet O, O’Gorman AM, Farmer J-P, et al. Use of theprone position in the MRI evaluation of spinal cord rethetering.Pediatr Neurosurg 1996;25:286–294.18. Ogiwara H, Lyszczarz A, Alden TD, et al. Rethetering oftransected fatty filum terminalis. J Neurosurg Pediatr 2011;7:42–46.19. Yong RL, Habrock-Bach TH, Vaughan M, et al. Symp-tomatic retethering of the spinal cord following section of a thightfilum terminale. Neurosurg 2011;68:1594–1602.20. Ostling LR, Bierbrauer KS, Kuntz C IV. Outcome,reoperation, and complications in 99 consecutive children oper-ated for thight or fatty filum. World Neurosurg 2012;77:187–191.Tethered Cord Syndrome 409

Tethered cord syndrome associated with a thickened filum terminale in a dog

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Tethered cord syndrome associated with a thickened filum terminale in a dog

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