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\title{Congenital kyphoscoliosis associated with thoracic hemivertebrae in a
nine-month-old Racking filly}



\author[1]{Samaneh Ghasemi}%
\author[2]{Mohammad Ali Sadeghi Balajorshari}%
\author[2]{Ali Mirshahi}%
\affil[1]{Ferdowsi University of Mashhad}%
\affil[2]{Ferdowsi University of Mashhad Faculty of Veterinary Medicine}%


\vspace{-1em}



  
  \date{May 25, 2024}


\begingroup
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\selectlanguage{english}
\begin{abstract}
Thoracic hemivertebra is one of the rare congenital vertebral anomalies
in horses resulting in vertebral column deformity with or without
neurological signs. A nine-month-old Racking filly was presented with a
distinct bump over the back region. This bump was apparent at birth and
has been increasing in size. Clinical examination revealed a painless
kyphoscoliosis over the thoracic vertebrae with mild ataxia and abnormal
gait of hindlimbs. In plain lateral radiographs of thoracic vertebrae,
hemivertebrae were seen in the 13th-15th thoracic vertebrae. At
myelography performed under general anaesthesia, the ventral and dorsal
aspects of the contrast medium column were narrowing at the level of the
13th-14th thoracic vertebrae, and no sign of contrast medium after the
14th thoracic vertebra that represents spinal cord compression. Little
information about hemivertebra in horses exists and a better
understanding of hemivertebra etiology is required.%
\end{abstract}%



\sloppy


Congenital kyphoscoliosis associated with thoracic hemivertebrae in a
nine-month-old Racking filly

Thoracic Hemivertebrae In A Racking Filly

Samaneh Ghasemi1, Mohammad Ali Sadeghi Balajorshari1, Ali Mirshahi1

1. Department of Clinical Sciences, Faculty of Veterinary Medicine,
Ferdowsi University of Mashhad, Mashhad, Iran

Correspondence

Samaneh Ghasemi

Email: s.ghasemi@um.ac.ir

Summary

Thoracic hemivertebra is one of the rare congenital vertebral anomalies
in horses resulting in vertebral column deformity with or without
neurological signs. A nine-month-old Racking filly was presented with a
distinct bump over the back region. This bump was apparent at birth and
has been increasing in size. Clinical examination revealed a painless
kyphoscoliosis over the thoracic vertebrae with mild ataxia and abnormal
gait of hindlimbs. In plain lateral radiographs of thoracic vertebrae,
hemivertebrae were seen in the 13th-15th thoracic vertebrae. At
myelography performed under general anaesthesia, the ventral and dorsal
aspects of the contrast medium column were narrowing at the level of the
13th-14th thoracic vertebrae, and no sign of contrast medium after the
14th thoracic vertebra that represents spinal cord compression. Little
information about hemivertebra in horses exists and a better
understanding of hemivertebra etiology is required.

KEYWORDS

Horse, filly, hemivertebra, kyphoscoliosis, thoracic

Key points

Developmental abnormalities of the thoracic vertebrae are rare in
horses.

Hemivertebra is a rare congenital spinal anomaly resulting from failure
of formation on one side of the vertebral body.

Hemivertebrae can lead to deformation of spine due to unbalanced spinal
growth, resulting in kyphosis, lordosis, or scoliosis with or without
neurologic gait deficits.

INTRODUCTION

The vertebral column, as a central axis of the skeleton, is composed of
alternating series of vertebrae (Ward et al., 2018). Several
developmental vertebral defects are occurred in horses, that cervical
vertebral stenotic myelopathy (CVSM) and occipitoatlantoaxial
malformation (OAAM) are relatively common developmental abnormalities
(Auer \& Stick, 2018; Crochik et al., 2009; Unt \& Piercy, 2009).
However, other congenital anomalies of the vertebral column including
atlantoaxial instability, block vertebrae, butterfly vertebrae,
hemivertebrae, and spina bifida, occur rarely in horses (Auer \& Stick,
2018). These conditions occur as a result of a failure of normal
formation, segmentation, differentiation, or union of structures during
embryologic development stages (Auer \& Stick, 2018;
Castriota-Scanderbeg \& Dallapiccola, 2006). Hemivertebra is a condition
in which asymmetric vertebral body formation occurs so, a part of the
vertebral body is deficient (Bertram et al., 2019; White \& Goldberg,
2022). Depending on hemivertebra location and severity, it may be
associated with moderate to severe angulation of the normal spine
alignment with or without neurologic gait deficits (Auer \& Stick, 2018;
Haussler). In horses, hemivertebra is a rare congenital vertebral
malformation, limited to reports of individual cases (de Heer \& Nout,
2011; Kirkberger \& Gottschalk, 1989; Wong et al., 2005). This case
report describes the clinical and radiographic findings of congenital
thoracic hemivertebrae in a nine-month-old Racking filly.

CASE HISTORY AND CLINICAL FINDINGS

A nine-month-old 153 kg Racking filly with a distinct bump over the back
region was referred to the Surgery Section of the Veterinary Teaching
Hospital of the Ferdowsi University of Mashhad. According to the owner,
this bump was present since her birth and increased in size over time.
There was no history of trauma. On physical examination the filly was
alert and her body condition was normal. The respiratory rate, heart
rate, and temperature were within normal limits. Examination of the
filly back revealed abnormal curvature of the spine along the sagittal
plane (kyphosis) with mild scoliosis (kyphoscoliosis) over the thoracic
vertebrae (Figure 1). No pain was detected on palpation of this region.
Any forelimbs deficits or cranial never abnormalities were not observed.
The cervical range motion was normal. Very mild ataxia and abnormal gait
in hindlimbs were observed on examination (grade 1/5). No urinary or
fecal incontinence was reported by her owner.

The blood sample was obtained and hematology and serum biochemistry
profiles were evaluated. Hematology parameters were within the normal
range. Biochemistry analyses showed a raised in aspartate
aminotransferase (AST: 393; reference range 226--366 U/L) and Creatine
kinase (CK: 1083; reference range 108--430 U/L). Plain and contrast
radiography was carried out. A myelogram was performed under general
anesthesia. For this purpose, the filly was sedated with 1.1 mg/kg of
xylazine (20 mg/ml; Alfasan; Holland) intravenously, followed by 0.1
mg/kg of diazepam (5 mg/ml; Zepadic\selectlanguage{ngerman}®; Caspian tamin Pharmaceutical Co.;
Iran). Then anaesthesia was induced by 2.2 mg/kg ketamine (100 mg/ml;
Alfasan; Holland) intravenously and was intubated orotracheally.
Anaesthesia was maintained with isoflurane (AErrane®; Baxter Healthcare
Corporation; USA). Myelographic evaluation was performed with the
cisternamagna technique. The area was aseptically prepared. The head was
maintained in a flexed position and an 18G spinal needle was placed in
the atlantooccipital space. After 50 ml cerebrospinal fluid (CSF) was
withdrawn, intrathecally injection of a similar volume of iodixanol 270
mg/ml (270 mg/ml; Visipaque\textsuperscript{TM}; GE Healthcar Inc.; USA)
was done for 3 minutes. Before imaging, the head was maintained in an
elevated position. In plain lateral radiographs of thoracic vertebrae,
multiple hemivertebrae were seen in the 13th-15th thoracic vertebrae
with several abnormal ribs (Figures 2 and 3). At myelography, no sign of
significant abnormality in contrast medium column was seen in lateral
and flexed radiographs of cervical myelography. In the thoracic region,
the ventral and dorsal aspects of the contrast medium column were
narrowing at the T13- T14, and the contrast medium was not passed that
revealing extradural compression of the spinal cord in mentioned
thoracic regions (Figure 4). Collected CSF was evaluated. Various
aspects of this disorder including its progression, treatment options,
outcomes, prognosis, and animal welfare were fully explained to the
owner, but the owner refused its management.

DISCUSSION

In horses, developmental vertebral disorders, commonly cause
malformations of the cervical vertebrae (de Heer \& Nout, 2011; Dorner
et al., 2022; Rendle et al., 2008; Unt \& Piercy, 2009; Wong et al.,
2005) while thoracic and lumbar vertebral malformations are infrequent
(de Heer \& Nout, 2011; Wong et al., 2005). Vertebral malformations can
be congenital (present at birth) or acquired (later in life) (Wong et
al., 2005). Hemivertebra is one of the congenital vertebral
abnormalities. Failure of chondrification centers to develop during the
formation or the segmentation during somitogenesis stages and failure of
ossification of the vertebra due to improper formation of the
intersegmental arteries of the vertebral column and therefore
alternation in vascular supply at the developmental stage has been
proposed as the pathogenesis of hemivertebra (Besalti et al., 2005;
Goldstein et al., 2005; Johal et al., 2016; Varras \& Akrivis, 2010).
Hemivertebrae can result in deviations of the vertebral column in the
sagittal plane dorsally (kyphosis), ventrally (lordosis), or medially
(scoliosis) (Auer \& Stick, 2018; Denoix, 2005).

In humans, hemivertebra is a rare congenital anomaly and its incidence
is estimated at 0.05\%-0.1\% and is more common in females (Shah et al.,
2020; Varras \& Akrivis, 2010; Xu et al., 2020). In animals,
hemivertebra is the most common congenital malformation in dogs (De
Rycke \& Saunders, 2017; Ryan et al., 2017; Schlensker \& Distl, 2016;
Wyatt et al., 2018). The breed-related incidence of hemivertebra in dogs
has been investigated and reported that hemivertebra is very common in
screw-tailed brachycephalic breeds with a prevalence range from 78\% to
94\% (Davitkov et al., 2020; Wyatt et al., 2018).

In a study, vertebral lesions have been reported in 202/443 horses
(38.6\%), with the main causes being crowding and overriding of the
dorsal spinous processes in the caudal thoracic and cranial lumbar
regions. A total of 15 horses (2.9\%) vertebral malformations including
scoliosis, lordosis, and kyphosis were identified (Jeffcott, 1980).

To date, only a few cases of hemivertebra in horses were reported
previously. According to these and the presented case report, the horses
affected by hemivertebra are of various breeds, including the Quarter
(Wong et al., 2005), Friesian (de Heer \& Nout, 2011), and American
saddle horse (Kirkberger \& Gottschalk, 1989). To our knowledge, this is
the first reported case of thoracic hemivertebra in the Racking horse.
In the previous case reports of hemivertebra, this condition was
described in male horses including geldings and colts (de Heer \& Nout,
2011; Kirkberger \& Gottschalk, 1989; Wong et al., 2005), but in the
present case, hemivertebra reported in female foal (a filly). However,
due to a few published case reports, it is difficult to find the
association between sex, breed, and incidence of hemivertebra in the
horse.

In agreement with the case reported by Wong (Wong et al., 2005), rib
anomalies were observed in our case. Ribs irregularity and structural
change were observed at radiography in this case. This finding detects
as an incidental finding on radiography or post-mortem specimens and
does not contribute to neurological signs (Denoix, 2005; Wong et al.,
2005). It has been shown that hemivertebra may be associated with other
congenital musculoskeletal anomalies including spine, limbs, and ribs
malformations, neural tube defects, and extramusculoskeletal anomalies
including the cardiac, genitourinary, central nervous system, and
gastrointestinal tract anomalies, probably due to anatomically
unbalanced growth between hemivertebra and structural differentiation of
surrounding spine (Bohiltea et al., 2022; Chaturvedi et al., 2018;
Moser, 2005; Varras \& Akrivis, 2010; Yang et al., 2020). Because the
structure of the ribs is formed in close association with vertebrae
during gestation, the same developmental failures that lead to
hemivertebra are attributed to rib abnormalities (Fischer \& Degenhardt,
2008).

In the present case, kyphoscoliosis was observed. It has been
demonstrated that Hemivertebra is one of the important causes of
deviation from the normal curvature of the spine because the growth
potential of the affected vertebrae is like the normal vertebrae (Yang
et al., 2020). This condition can result in different structural
deformities of the spinal axis including scoliosis, lordosis, and/or
kyphosis (Xu et al., 2020). Structural abnormalities may affect the
spinal cord so, a neurological examination should be considered to
determine the neurological signs (Kaplan, Spivak, \& Bendo, 2005).

Based on the published data about hemivertebra and spine curvature
disorders in horses, this condition may be associated with neurological
deficits or not (Denoix, 2005; Wong et al., 2005). Even, though it has
been noted that the horses with deviations of thoracolumbar without any
neurological deficit can be undergoing normal use, these horses are
predisposed to intervertebral osteoarthrosis (Denoix, 2005). Unlike the
thoracolumbar region, the hemivertebra and deviations of the cervical
spine are usually accompanied by neurological deficits (Denoix, 2005).
Kirberger and Gottschalk reported a foal affected by Kyphoscoliosis of
the thoracolumbar spine (T7-L4) and hemivertebra at T15 but, no
neurological deficits were detected (Kirkberger \& Gottschalk, 1989).
Wong et al described a 9-month-old Quarter gelding with severe hindlimb
ataxia and paresis were associated with multiple thoracic malformations
of T4-T8 including hemivertebrae, kyphosis, and fused dorsal spinous
processes (Wong et al., 2005). In another report by de Heer and Nout, a
5-day-old Friesian colt was presented for kyphosis at the level of
T18--L4 that was affected by neurological deficits including pelvic limb
paraparesis and severe ataxia (de Heer \& Nout, 2011). In the case
report published by Kothstein et al, acquired kyphosis a due to
compression fractures of T14 to T18 in association with mild hindlimb
ataxia was described in a 20-month-old horse (Kothstein et al., 2000).
Rendle et al reported a kyphosis of the thoracolumbar spine with
thoracic neurenteric cyst and butterfly vertebrae at T6 and T7 in a
seven-month-old colt that suffered from very severe neurologic deficits
(Dorner et al., 2022). In the presented filly here, a mild neurological
deficit was observed in hindlimbs that may be due to compression and
narrowing of the spinal cord at the T13. It has been described that
several factors such as the severity of kyphosis, hemivertebra subtype,
breeds, and presence of other pathologic conditions may be associated
with the presence or absence of neurological signs in dogs with
hemivertebra (De Decker et al., 2019). However, the development of
clinical signs related to hemivertebra in horses is not completely
known.

Increased AST and CK were observed in our case and these changes may be
related to kyphoscoliosis. Spinal misalignment can alter body
biomechanics and muscles loading so, kyphosis may be attributed to
several muscle impairments (Briggs et al., 2007; Fasser et al., 2021).
Although an elevation in serum CK along with AST is an indication of
muscle damage, these enzymes may be affected by other different factors
(Harris et al., 1990; Satué et al., 2022).

The etiological factors causing vertebral malformations have not been
fully explained in horses, but genetic and heredity factors, dietary
imbalances, toxic factors, hormonal changes, environmental cusses,
trauma, and in-utero insult may be responsible (Auer \& Stick, 2018;
Dorner et al., 2022; Kirkberger \& Gottschalk, 1989; Kothstein et al.,
2000; Unt \& Piercy, 2009; Wong et al., 2005). It has been mentioned
that alteration in genes expression, especially members of Hox family,
may contribute to malformations of the axial skeleton and vertebrae (Unt
\& Piercy, 2009). However, the role of genetics, heredity and other
factors of hemivertebra in horses are generally considered unknown,
probably because of the rarity of the condition. The etiology of the
present case here remains undetermined as well as other previous
hemivertebra case reports (de Heer \& Nout, 2011; Wong et al., 2005).
Although there were no similar congenital anomalies in filly parents the
owner had no knowledge about previous generations. Also, there was no
known exposure to toxic substances or trauma. However, since this
condition was present at birth, genetics may probably be explaining the
anomaly in this case.

Although in humans, early diagnosis and appropriate surgical management
are recommended before the development of neurological signs or severe
deformity and disability (Han et al., 2011; Oksanen et al., 2021; Ruf et
al., 2006; Yang et al., 2020)but, there is no treatment for this
condition in horses (Auer \& Stick, 2018). In dogs, surgical management
of cases with clinical signs associated with hemivertebra with vertebral
column malangulation can be challenging, and there are only a few
reports of such cases in the veterinary literature (Charalambous et al.,
2014).

Congenital thoracic hemivertebra in horses is a rare anomaly that may be
with a deformity resulting in congenital scoliosis and kyphosis. This
condition may also cause spinal cord compression and neurological signs.
Rib anomalies may occur in association with hemivertebra. The actual
incidence and prevalence of thoracic hemivertebra in horses are little
known and future reports are required to better understand the different
aspects of such an anomaly.

AUTHOR CONTRIBUTIONS

All the authors contributed to the clinical examinations, interpretation
of the clinical data, and preparation of the manuscript. All authors
approved the final version of the manuscript.

CONFLICT OF INTEREST

No conflicts of interest have been declared.

FUNDING

No funding was received.

ETHICS STATEMENT

This case reports details the management of a clinical case that was a
part of the clinical caseload. High veterinary care has been performed
with the consent of the animal owner. All identifying information has
been removed.

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Figure legends

Figure 1. Clinical appearance of thoracic kyphoscoliosis in the
presented filly

Figure 2. Schematic representation of the abnormality in vertebrae
noted. Grey shadow areas show abnormal shape of the 12th-16th thoracic
vertebrae and wedge shape in body of the 13th-15th thoracic vertebrae.

Figure 3. Laterolateral radiograph of the thoracic vertebrae in the mid
to caudal thoracic region. Kyphosis shows in the caudal-thoracic region
of the spine caused by hemivertebrae in the 13th-15th thoracic
vertebrae.

Figure 4. Laterolateral radiograph of the caudal thoracic vertebrae
shows an abnormal myelogram. Note that narrowing of the ventral contrast
medium column at the level of the 12th thoracic vertebrae. The ventral
and dorsal contrast medium columns are narrower at the level of the
13th-14th thoracic vertebrae and no sign of contrast medium after 14th
thoracic vertebra that represent spinal cord compression.\selectlanguage{english}
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