BELTRAN

CHANG

DE RISIO

FENN

GRIFFITHS

HANSEN

MARI

MCKEE

TAYLOR-BROWN

English

Beltran, E

RVC Research Online

  RVC OPEN ACCESS REPOSITORY – COPYRIGHT NOTICE  This is the peer-reviewed, manuscript version of an article published in Veterinary Record. The final version is available online via http://dx.doi.org/10.1136/vr.j5494.  The full details of the published version of the article are as follows:  TITLE: Acute hydrated non-compressive nucleus pulposus extrusion: what do we know so far? AUTHORS: Elsa Beltran JOURNAL TITLE: Veterinary Record PUBLISHER: BMJ Publishing Group PUBLICATION DATE: 30 November 2017 (online) DOI: 10.1136/vr.j5494. ACUTE HYDRATED NON-COMPRESSIVE NUCLEUS PULPOSUS EXTRUSION, WHAT DO WE KNOW SO 1 FAR? 2 Elsa Beltran 3  4 An acute extrusion of non-degenerated nucleus pulpous material through a tear of the annulus 5 fibrosus can occur after sudden changes of intradiscal pressure and biomechanics (for example during 6 a vigorous exercise, running, jumping). This type of intervertebral disc extrusion can be characterised 7 as compressive or non-compressive and it is being more commonly recognised and studied as the 8 cause of acute myelopathy in dogs and less frequently in cats.1–6 9 The term acute non-compressive nucleus pulposus extrusion was proposed to indicate when the 10 extruded hydrated (as description of non-degenerated) nucleus pulposus contuses the spinal cord and 11 dissipates within the epidural space without significant spinal cord compression.2 Other terms have 12 been used to describe this type of intervertebral disc extrusion including: high velocity low-volume 13 disc extrusion, traumatic disc extrusion, dorsolateral intervertebral disc explosion, traumatic disc 14 prolapse and erroneously also Hansen type III intervertebral disc disease.1,2,4,7 From all the terms used, 15 the one that ideally should be avoided is Hansen type III as Hansen described intervertebral disc 16 degenerations (type I and type II) and this particular type of disc disease is non-degenerated and, 17 moreover, it was never described by Hansen.8 18 A new study on this type of intervertebral disc extrusion (summarised in page 549 of this week’s issue 19 of Veterinary Record) proposed adding the word hydrated to differentiate it from the degenerated 20 and potentially non-compressive/minimally compressive Hansen type I intervertebral disc extrusion, 21 calling it then acute hydrated non-compressive nucleus pulposus extrusion (AHNCNPE).  22 The clinical presentation of dogs with AHNCNPE is characterised by peracute onset of often lateralised 23 myelopathy that is non-progressive after the first 24 hours with some degree of physical activity at 24 the time of the onset (Figure 1). Lateralisation of neurological deficits has been reported in around 25 60% of dogs (similar to recent study of this week’s issue by Ros and others) however in one study the 26 lateralisation of the clinical sings was reported in up to 90% of the affected dogs.9 Discomfort or 27 hyperalgesia during palpation of the affected area have been described in up to 57% of dogs with 28 AHNCNPE at the time of the onset, however it is unlikely that this clinical sign sustained or become 29 severe after 24 hours. Any canine breed and rarely cats can be affected. Male dogs seem to be affected 30 more commonly than females. The age at diagnosis in dogs is usually around 6 years (range 2 to 12 31 years of age).2,5,9,10 The T3-L3 spinal cord segments and in particular the T12-T13, T13-L1, and L1-L2 32 intervertebral disc spaces are most commonly affected.  33 It is important to emphasised that based on the signalment, history and neurological examination a 34 high clinical index of suspicion for AHNCNPE can be reached. The clinical presentation can be very 35 similar to ischaemic myelopathy (for instance in cases of fibrocartilaginous embolic myelopathy 36 (FCEM)). A recent study from Fenn and others compared the clinical presentation in dogs with 37 presumptive ischaemic myelopathy and dogs with AHNCNPE.9 This study concluded that dogs with 38 AHNCNPE were signicantly older at disease onset and were more likely to have a history of vocalization 39 at onset of clinical signs and have hyperesthesia on palpation of the vertebral column during initial 40 examination compared with dogs with ischemic myelopathy. A definitive diagnosis of AHNCNPE is only 41 possible at post-mortem examination; however, the combination of clinical presentation and 42 magnetic resonance imaging (MRI) findings provides the mainstay of presumptive antemortem 43 diagnosis.2,11 44 The MRI features compatible with AHNCNPE (Figure 2) include evidence of reduced volume of the 45 nucleus pulposus, focal hyperintensity within the overlying spinal cord on T2-weighted images, 46 extraneous material or signal changes in the epidural space, and minimal to no spinal cord 47 compression.2,4,11 48 On the other hand, some owners might have financial restriction or MRI might not be available in 49 some institutions during out of hours. On these circumstances, other imaging modalities (such as 50 myelogram or computed tomography) could be considered to exclude compressive myelopathies with 51 an acute onset (for instance Hansen type I intervertebral disc extrusion) and therefore contribute to 52 the presumptive diagnosis of AHNCNPE. 53 To date, little data have been published on the myelographic appearance of AHNCNPE.5 McKee and 54 other reported radiographic and myelographic features in 48 dogs with presumptive AHNCNPE, 55 however none of the affected dogs had MRI and therefore some minimally compressive Hansen Type 56 I intervertebral disc extrusions could have been included. The recent study by Ros and others describes 57 the myelographic appearance of 21 dogs with suspected AHNCNPE (diagnosed on MRI findings): all 58 dogs had intramedullary patterns (attenuation of both contrast columns), 57% of the dogs showed 59 extradural pattern and the affected intervertebral disc was narrowed in all the dogs. The length of 60 spinal cord swelling measured on myelogram is a controversial indicator for prognosis and this was 61 supported by the study of Ros and others, where spinal cord swelling (measured by myelogram) did 62 not associate with neurological grade or outcome. 63 When evaluating MRI of affected dogs with AHNCNPE, it is obvious the reduced volume of the 64 extruded nucleus pulposus on transverse planes (Figure 3) and sagittal planes of T2W images, however 65 this finding has not been previously evaluated or associated to the clinical presentation. Ros and 66 others measured the volume of the affected nucleus pulposus, compared that volume with the mean 67 volume of the two-adjacent intervertebral discs and concluded that the extruded volume of the 68 nucleus pulposus was significantly associated with the neurological grade at presentation. 69 Outcome of AHNCNPE is successful in the majority of the dogs. A recent large study by Mari and 70 others10 reported successful outcome (ambulatory without assistance and complete urinary and faecal 71 continence) in 73% of the dogs. This study also found that dogs with AHNCNPE were five times more 72 likely to develop faecal incontinence (23% of the affected dogs) than dogs with suspected ischaemic 73 myelopathy, enhancing the benefits of diagnosing these conditions by MRI to further evaluate possible 74 outcomes. 2,9–11 75 Despite the reported myelographic findings by Ros and others, MRI should still be considered the gold 76 start imaging modality for the diagnosis of ANNPE. Myelography can provide useful information in 77 emergency situations to assess the degree of spinal cord compression and therefore the need to bring 78 that patient to surgery if indicated. 79  80 Clinical importance for practitioners 81  Dogs with acute hydrated non-compressive nucleus pulposus extrusion (AHNCNPE) present 82 with characteristic clinical signs 83  The signalment, history and neurological examination provide a high clinical index of suspicion 84 for AHNCNPE 85  The mainstay of presumptive antemortem diagnosis can be reached with the combination of 86 clinical presentation and MRI findings 87  Myelography could help to rule out surgical conditions when there are financial restrictions 88 or advanced imaging is not available 89  AHNCNPE has a good outcome in the majority of the dogs 90  Dogs with AHNCNPE are at risk of developing faecal incontinence  91  92  93 1.  GRIFFITHS I. A syndromeproduced by dorso-;atera; “explosions” of the interverterbal discs. 94 Vet Rec. 1970;87:737–41.  95 2.  DE RISIO L, ADAMS V, DENNIS R, et al. Association of clinical and magnetic resonance imaging 96 findings with outcome in dogs with presumptive acute noncompressive nucleus pulposus 97 extrusion: 42 cases (2000–2007). J Am Vet Med Assoc.2009;234(4):495–504. 98 3.  BELTRAN E, DENNIS R, DOYLE V, et al. Clinical and magnetic resonance imaging features of 99 canine compressive cervical myelopathy with suspected hydrated nucleus pulposus 100 extrusion. J Small Anim Pract. 2012;53 (February):101–7.  101 4.  CHANG Y, DENNIS R, PLATT SR, et al. Magnetic resonance imaging of traumatic intervertebral 102 disc extrusion in dogs. Vet Rec. 2007;160(23):795–9.  103 5.  MCKEE WM, DOWNES CJ, PINK JJ, et al. Presumptive exercise-associated peracute 104 thoracolumbar disc extrusion in 48 dogs. Vet Rec [Internet]. 2010;166(17):523–8.  105 6.  TAYLOR-BROWN FE, DE DECKER S. Presumptive acute non-compressive nucleus pulposus 106 extrusion in 11 cats: clinical features, diagnostic imaging findings, treatment and outcome. J 107 Feline Med Surg [Internet]. 2017;19(1):21–6.  108 7.  LU D, LAMB CR, WESSELINGH K, et al. Acute intervertebral disc extrusion in a cat: Clinical and 109 MRI findings. J Feline Med Surg. 2002;4(1):65–8.  110 8.  HANSEN HJ. A pathologic-anatomical study on disc degeneration in dog. Acta Orthop Scan. 111 1952;11:4–119.  112 9.  FENN J, DREES R, VOLK HA, et al. Comparison of clinical signs and outcomes between dogs 113 with presumptive ischemic myelopathy and dogs with acute noncompressive nucleus 114 pulposus extrusion. J Am Vet Med Assoc. 2016;249(7):767–75. 115 10.  MARI L, BEHR S, SHEA A, et al. Outcome comparison in dogs with a presumptive diagnosis of 116 thoracolumbar fibrocartilaginous embolic myelopathy and acute non-compressive nucleus 117 pulposus extrusion. Vet Rec. 2017;vetrec-2016-104090.  118 11.  FENN J, DREES R, VOLK HA, et al. Inter- and intraobserver agreement for diagnosing 119 presumptive ischemic myelopathy and acute noncompressive nucleus pulposus extrusion in 120 dogs using magnetic resonance imaging. Vet Radiol Ultrasound. 2016;57(1):33–40.  121  122 Figure Legends  123  124 Figure 1 - 6 years old Staffordshire Terrier Crossed, female spayed with peracute onset of 125 ambulatory paraparesis with spontaneous knuckling on the left pelvic limb after playing in 126 the park. She was diagnosed with an acute hydrated non-compressive nucleus pulposus 127 extrusion at the level of L1-L2 intervertebral disc. 128  129 Figure 2 - (A) Sagittal T2-weigthed image of the thoracolumbar spine of an 11yo dog with peracute 130 onset of left pelvic limb monoplegia. There is focal hyperintensity within the spinal cord 131 overlying the IVD L2-L3 with reduction in volume of the nucleus pulposus (black arrow head). 132 (B) Transverse T2-weighted image; (C) transverse T1-weighted FSE image. There is a focal 133 area of hyperintesitiy on T2W within the spinal cord parenchyma lateralised to the left 134 (asterisk) and signal change within the epidural fat (black arrow) on the same side (B, C) with 135 minimal spinal cord compression. 136  137 Figure 3- Transverse T2 weighted images at the level of L1-L2 intervertebral disc (A), at the level of 138 L2-L3 (B, same case as Figure 2, AHNCNPE at L2-L3) and at the level of L3-L4 (C). The volume 139 of the affected nucleus pulposus is reduced (B) compared with the cranial and caudal 140 adjacent disc (A,C). 141  142 

Acute hydrated non-compressive nucleus pulposus extrusion: what do we know so far?

Acute hydrated non-compressive nucleus pulposus extrusion: what do we know so far?

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