Skeletal aspects of the atlanto-occipital fusion in a Japanese brown calf.

Atlanto-occipital fusion in a Japanese Brown calf was examined morphologically, paying special attention to skeletal changes. At the craniovertebral junction, the basal occipital bone fused to the cranial extremity of the ventral arch of the atlas with the rudiment of the atlantal centrum. The dens was not formed at the axis. These changes suggest that a hypocentrum and a centrum of the atlas derived from the first cervical sclerotome had failed to separate the occipital base from the proatlantal sclerotome including the apical element of the dens. Although a developmental disturbance at the cervical and thoracic vertebrae was also associated, critical neurological signs such as ataxia and paralysis were absent.     

Development and Variation of the Lateral Vertebral Foramen of the Atlas in Dogs

Postnatal development and variation of the bony cranial border of the lateral vertebral foramen (LVF) of the atlas was studied in 96 dogs. Developmental ossification was investigated in 8 known-aged Miniature Schnauzer pups, after each atlas was prepared either as an alizarin-red stained clearing or as a dried cleaned bone. Variation was investigated in 63 atlases from mature dogs and by study of radiographs from 25 mature dogs of various breeds. The soft tissue structures passing through the LVF and attaching to its cranial border were dissected in an additional 2 embalmed and 2 fresh cadavers. In 2-week-old pups, the LVF was represented by a notch in the cranial margin of the bony arch of the atlas, with a cartilage bar completing the foramen cranially. Between 6 and 16 weeks the bar forming the cranial bony border of the LVF ossified in its preexisting cartilage anlage. In mature dogs, the LVF was present in the craniolateral aspect of the arch of the atlas and was recognized on lateral radiographs. The vertebral artery and vein, and first cervical nerve passed through the LVF and the atlantooccipital joint capsule and dorsal membrane attached to the cranial border of the LVF. In one dog the cranial border of the LVF of the atlas was incompletely ossified bilaterally. This developmental variant was compared with variations in man and other mammals, and with proatlas neural arch derivatives.     

INCOMPLETE OSSIFICATION OF THE ATLAS IN DOGS WITH CERVICAL SIGNS

Osseous defects affecting the atlas were identified in computed tomography and magnetic resonance images of five dogs with cervical signs including pain, ataxia, tetraparesis, or tetraplegia. Osseous defects corresponded to normal positions of sutures between the halves of the neural arch and the intercentrum, and were compatible with incomplete ossification. Alignment between the portions of the atlas appeared relatively normal in four dogs. In these dogs the bone edges were smooth and rounded with a superficial layer of relatively compact cortical bone. Displacement compatible with unstable fracture was evident in one dog. Concurrent atlantoaxial subluxation, with dorsal displacement of the axis relative to the atlas, was evident in four dogs. Three dogs received surgical treatment and two dogs were treated conservatively. All dogs improved clinically. Incomplete ossification of the atlas, which may be associated with atlantoaxial subluxation, should be considered in the differential diagnosis of dogs with clinical signs localized to the cranial cervical region.     

Occipitoatlantoaxial malformation with duplication of the atlas and axis in a half Arabian foal

An unusual occipitoatlantoaxial malformation is described in a 2-week-old male part Arabian foal that was unable to stand at birth and showed signs of spastic tetraparesis due to a cervical spinal cord compression. There were 2 atlases present. One was fused to the occipital bones. The other articulated with the first atlas and an axis which had a long dens that projected into the vertebral canal. Examination of the ossification centers of the axis indicated partial duplication of that bone.     

COMPUTED TOMOGRAPHY VARIATIONS IN MORPHOLOGY OF THE CANINE ATLAS IN DOGS WITH AND WITHOUT ATLANTOAXIAL SUBLUXATION

Computed tomography images of 120 dogs were reviewed to characterize variations in atlas morphology, and to identify breed‐specific morphologic features. The neural arch of the atlas was thicker in large dogs and male dogs than in small dogs, having a layer of trabecular bone between the inner and outer layers of compact bone. The transverse processes of the atlas were relatively longer in large dogs than in small dogs. Twelve (10%) dogs had incomplete ossification of the atlas. Incomplete ossification of the atlas was associated with gun dogs. Eight dogs had atlantoaxial subluxation. All eight dogs with atlantoaxial subluxation had cervical signs, whereas none of the seven dogs with incomplete ossification of the atlas unaccompanied by atlantoaxial subluxation had clinical signs referable to that area. Of five dogs with both atlantoaxial subluxation and incomplete ossification of the atlas, four had osseous defects affecting both the intercentrum and neural arch, and one had only an osseous defect affecting the neural arch. There was a strong association between incomplete ossification of the atlas and atlantoaxial subluxation (odds ratio 35.0, 95% CI 7.0–175, P=0.00002), which supports the hypothesis that incomplete ossification of the atlas predisposes dogs to atlantoaxial subluxation.     

X-ray and CT morphology of atlas variants in the dog

To investigate variations in atlas shape in dogs the image archives of the Department for Small Animals and Horses, University of Vienna, and The Royal Veterinary College, University of London were searched for radiographs and CT images of the canine atlas. 32 radiographic and 78 CT studies, including 51 toy and 54 large breed dogs, were retrieved and analysed. Five dogs had both radiographs and CT scans. Patients with pathologic alterations, such as fractures and incomplete ossification of the atlas, as well as oblique projections were excluded. Compared to large breed dogs (body weight more than 30 kg) the atlas of toy breed dogs (body weight less than 10 kg) had a reduced craniocaudal and an increased dorsoventral diameter. The vertebral longitudinal axis appeared to be dorsorotated, resulting in a steeper rise of the atlas wings and a more dorsally located lateral vertebral foramen. When comparing the atlas of toy and large breed dogs, the distribution of three morphologic parameters was statistically different: Ratio length to height (toy breeds > 1, large breeds < or = 1), shape of the vertebral chanal (toy breeds: vertically oval, large breeds: round resp. cross-oval, or vertically oval) and trabecular bone of the dorsal arch (toy breeds: absent, large breeds: present). There was no significant difference in the morphology of the ventral arch. Differences in atlas morphology could contribute to the predisposition of toy breed dogs to atlanto-axial instability; however, further studies are necessary to test this hypothesis.     

Atlantoaxial malformation in a half-Arabian colt

A 1-year-old half-Arabian colt was referred for evaluation of a cranial cervical abnormality. Physical examination revealed the left wing of the atlas to be more ventral than the right wing. A head tilt, with the pole deviated to the left, was present because of the malpositioned atlas. Neurologic examination identified symmetrical weakness, ataxia, and proprioceptive deficits in all four limbs. Radiographs of the cranial cervical region revealed fusion of the atlas and axis, and deviation of the atlantoaxial joint to the left of the median plane. Euthanasia was elected. Necropsy confirmed the radiographic findings. The atlas was rotated 20 degrees counterclockwise when viewed from the caudal aspect. Multifocal myelomalacia was present in the first and second cervical spinal cord segments. The malformation was believed to be due to a degenerative process or abnormal embryological development.     

The Foramina of the Cervical Vertebrae of the Ox

All the macroscopically visible foramina of the atlas and axis in 20 oxen are examined and their size, incidence and connections described. The atlas possesses a canal connecting the atlantal fossa with the vertebral foramen. It is suggested that it be named “Canalis vertebroalaris”. The axis contains a prominent transverse canal rather than a foramen, with “cranial” and “caudal transverse foramina”. The canal occurs in an atypical location in 25 % of cases.     

A system of grading ossification in limbs of foals to assist in radiologic interpretation.

Tetracycline-labeled bones of 23 foals from 52 to 104 days old were sectioned and macroscopically examined to assess the extent of ossification or fusion of ossification centers. A grading system was devised with which to record information about the ossification centers and growth plates. The objective was to define anatomic standards which could contribute toward obtaining an accurate radiologic interpretation. Labeled limb bones of 3 neonatal foals were similarly treated, but grading of these was limited to the consideration of whether each site was still cartilaginous or had commenced to ossify.     

Laminectomy for relief of atlantoaxial subluxation in four horses

Malalignment of the atlas and axis was seen in 4 horses with an idiopathic form of atlantoaxial subluxation characterized by spinal cord compression on extension. The bone structure and density of the atlas and axis were radiographically normal in 3 of the 4 horses. Clinical signs appeared when the horses were 6 to 30 months old, and 3 of the 4 horses had a history of trauma. Although a congenital anomaly could not be ruled out, the cause was thought to be trauma. The horses were moderately to severely ataxic at the time of examination. Myelography revealed compression of the spinal cord at the atlantoaxial junction on extension. Flexion completely relieved the compression. In each horse, subtotal laminectomy of the caudal two thirds of the dorsal arch of the atlas was used to relieve the spinal cord compression. Two horses recovered fully, one had residual grade-1 neurologic deficits, and a fourth was euthanatized after it fractured a limb 6 weeks after surgery.     

Fascial compartments of the equine crus

The deep fascia of the equine crus was dissected grossly and separated into 2 layers, the superficial and deep laminae of the deep fascia. Attachments of these fascial laminae to the tibia and fibula formed 5 separate osteofascial compartments: cranial, lateral, caudal deep, caudal intermediate, and caudal superficial. Cranial tibial vessels and the deep peroneal nerve entered the cranial compartment through separate fascial hiatuses; this may predispose the equine crus to the occurrence of compartmental syndromes with clinically recognizable neural deficits.     

Congenital occipitoatlantoaxial malformations in the horse

From a clinical, radiological and morphological study of 9 horses with congenital malformations of the occiput, atlas and axis, and from a study of 2 reported cases, 3 diseases were defined: A. Familial occipitalisation of the atlas with atlantalisation of the axis in Arabian horses (7 cases in this report and the case reported by Leipold, et al., 1974). These horses had congenital atlantooccipital fusion, hypoplasia of the atlas and dens, malformation of the axis and modification of the atlantoaxial joint. B. Congenital asymmetrical occipitoatlantoaxial malformation (2 cases in this report). A Standardbred and a Morgan horse had atlantooccipital fusion, a wedge shaped vertebral piece attached to the caudal end of the axis and sigmoid scoliosis of the cervical vertebrae. C. Asymmetrical atlantooccipital fusion (the case reported by Schmaltz, 1915). This horse of an unknown breed had asymmetrical fusion between the atlas and occiput and cervical scoliosis. The clinical syndromes shown by horses with these malformations were variable but were broadly classified as: 1. Foal dead at birth, seen in one foal with A. 2. Tetraparesis at birth, seen in 5 foals with A. These foals were born with signs varying from tetraparesis to tetraplegia. 3. Progressive ataxia, seen in 2 foals with A. Clinical signs were due to a progressive focal cervical compressive myelopathy. 4. Congenital cervical scoliosis/deviated head, seen in the 2 horses with B and the horse with C. These horses had no signs of spinal cord or brain disease. The diagnoses were made clinically by palpation of the occipitoatlantoaxial region and were confirmed radiographically and/or by post mortem examination in all except one case. Pedigree analysis showed the familial nature of the particular occipitoatlantoaxial malformation seen in horses of only the Arabian breed.     

Ossification of the Atlas-Axis Complex in the Dog*

Skeleton preparations of 200 Beagles of known age, ranging from embryos at 28 days of age to 10 year old adults were studied. Preparations of gross specimens were examined with the aid of Alizarin red staining, binocular dissection and histological sections. Ossification centers for the components of the atlas and axis were identified and followed to their fusion. The developmental ossification sequence for these bones is described and compared with that of other similar studies in other species.     

Craniocervical junction in dogs revisited--new ligaments and confirmed presence of enthesis fibrocartilage

The study was performed to investigate and to describe features of gross and microscopic morphology of craniocervical junction (CCJ) in dogs. Seventy mature dogs (38 females, 32 males) of different body weight, representing small, medium and large breeds of dolicho-, mesati-, and brachycephalic morphotype were dissected. Morphological details were localised using an operating microscope with integrated video channel. Occurrence and distribution of fibrocartilage in the ligaments from 10 dogs was analysed histologically. Three new pairs of ligaments were described and named: dorsal ligaments of atlas, cranial internal collateral ligaments of atlas, and caudal internal collateral ligaments of atlas. Several new findings in the course of the known ligaments were found relating to breed and body weight. For the first time enthesis fibrocartilage was identified in ligaments of CCJ in dogs. Sesamoidal fibrocartilage was identified in the transversal ligament of atlas in large dogs. The findings are discussed for clinical importance.     

The topography of the thoraco-abdominal viscera in the ostrich (Struthio camelus)

The topography of the thoraco-abdominal viscera in the ostrich was studied in 20 birds varying in age from 2 weeks to 12 months. The lungs occupied the dorsal third of the thorax, and the heart lay in the cranioventral thorax perpendicular to the long axis of the body. There was no pleural cavity. The liver was situated in the caudoventral part of the thorax, and the proventriculus occupied the left cranial part of the abdomen between the 7th vertebral rib and the acetabulum. The gizzard lay in the cranioventral part of the abdomen, resting on the sternum and abdominal floor. The duodenum formed a loop from right to left, with the pancreas lying between the 2 limbs of the loop. The coiled jejunum and ileum occupied the ventral part of the abdomen between the gizzard and pelvis. The two caeca lay on either side of the terminal ileum with their apices in the pelvis. The rectum was the longest part of the intestine and could be divided into a thick proximal segment situated in the right dorsal part of the abdomen, and a thin distal part that occupied the left caudodorsal part of the abdomen. The trilobed kidneys lay along the ventral surface of the synsacrum, with the adrenal glands at their cranioventral poles. The testes lay ventrally to the cranial divisions of the kidneys, whereas the left ovary was situated ventrally to the cranial division of the left kidney. The spleen lay wedged in between the right kidney, caudal vena cava and proventriculus. The thyroid glands were situated at the cranial borders of the subclavian arteries, and the thymus lay at the base of the neck.     

Macro anatomical investigations of the cranial cervical ganglion in domestic pig (Sus scrofa domesticus)

In this study, the left and right cranial cervical ganglia (ganglion cervicale craniale) of eight young (four male, four female) domestic pigs weighing around 70-80 kg were inspected macro anatomically. The cranial cervical ganglion (CCG) was found cranio-ventrally of the distal ganglion of the vagus nerve, medial of the jugular process extremity, ventral of the atlas, dorsal of the epiglottis base and medial of the common root (CR) established by the internal carotid and occipital arteries. The internal carotid nerve and jugular nerve ramified from the cranial part of CCG. The jugular nerve gave branches that merged with the vagus and glossopharyngeal nerves. Other nerve branches originating from the cranial part of the ganglion reached to the external carotid artery and CR. The internal carotid nerve varied among cadavers in number of branches (two to four). These branches did not travel along the side of the internal carotid artery. The central part of CCG gave thin nerve branches that reached to various anatomical structures including the first and second cervical nerves, wall of the pharynx, accessory nerve, hypoglossal nerve, vagus nerve, external carotid artery and CR. The caudal part of CCG gave nerve branches that merged with the vagus, cranial laryngeal nerves, and common carotid artery. The external carotid nerves, which were two or three in number, also originated from the caudal part of CCG. In conclusion, the nerves ramifying from CCG of the pig varied in number among cadavers. Compared with literature raised in other species, there are also differences in number of nerve branches and course pattern of these nerves.     

Surgical decompression for traumatic atlantoaxial subluxation in a weanling filly.

A filly with ataxia and splinting and crepitation in the neck was found to have atlantoaxial subluxation. Radiographic diagnosis was based on the same criteria as those used in other species, ie, increased distance between the atlas and spine of the axis and increased distance between the dens and floor of the atlas. Extensive hemilaminectomy was performed to decompress the spinal cord. Stabilization was not attempted. Immediate postoperative response was encouraging, but the untimely death of the filly prevented further evaluation of the procedure.     

Atlanto‐Axial Malformation and Instability in Dogs with Pituitary Dwarfism due to an LHX3 Mutation

Background

Canine pituitary dwarfism or combined pituitary hormone deficiency (CPHD) in shepherd dogs is associated with an LHX3 mutation and can lead to a wide range of clinical manifestations. Some dogs with CPHD have neurological signs that are localized to the cervical spine. In human CPHD, caused by an LHX3 mutation, anatomical abnormalities in the atlanto‐axial (C1‐C2) joint have been described.

Objectives

To evaluate the presence of atlanto‐axial malformations in dogs with pituitary dwarfism associated with an LHX3 mutation and to investigate the degree of similarity between the atlanto‐axial anomalies found in canine and human CPHD patients with an LHX3 mutation.

Animals

Three client‐owned Czechoslovakian wolfdogs and 1 client‐owned German shepherd dog, previously diagnosed with pituitary dwarfism caused by an LHX3 mutation, with neurological signs indicating a cervical spinal disorder.

Methods

Radiography, computed tomography, and magnetic resonance imaging of the cranial neck and skull, necropsy, and histology.

Results

Diagnostic imaging identified abnormal positioning of the dens axis and incomplete ossification of the suture lines between the ossification centers of the atlas with concurrent atlanto‐axial instability and dynamic compression of the spinal cord by the dens axis. The malformations and aberrant motion at C1–C2 were confirmed at necropsy and histology.

Conclusions and Clinical Importance

The atlanto‐axial abnormalities of the dwarf dogs resemble those encountered in human CPHD patients with an LHX3 mutation. These findings suggest an association between the LHX3 mutation in dogs with CPHD and atlanto‐axial malformations. Consequently, pituitary dwarfs should be monitored closely for neurological signs.     

The spinal nerves that constitute the lumbosacral plexus and their distribution in the chinchilla

In this study, the spinal nerves that constitute the lumbosacral plexus (plexus lumbosacrales) (LSP) and its distribution in Chinchilla lanigera were investigated. Ten chinchillas (6 males and 4 females) were used in this research. The spinal nerves that constitute the LSP were dissected and the distribution of pelvic limb nerves originating from the plexus was examined. The iliohypogastric nerve arose from L1 and L2, giving rise to the cranial and caudal nerves, and the ilioinguinal nerve arose from L3. The other branch of L3 gave rise to the genitofemoral nerve and 1 branch from L4 gave rise to the lateral cutaneous femoral nerve. The trunk formed by the union of L4-5 divided into medial (femoral nerve) and lateral branches (obturator nerve). It was found that the LSP was formed by all the ventral branches of L4 at L6 and S1 at S3. At the caudal part of the plexus, a thick branch, the ischiadic plexus, was formed by contributions from L5-6 and S1. This root gave rise to the nerve branches which were disseminated to the posterior limb (cranial and caudal gluteal nerves, caudal cutaneous femoral nerve and ischiadic nerve). The ischiadic nerve divided into the caudal cutaneous surae, lateral cutaneous surae, common fibular and tibial nerve. The pudendal nerve arose from S1-2 and the other branch of S2 and S3 formed the rectal caudal nerve. The results showed that the origins and distribution of spinal nerves that constitute the LSP of chinchillas were similar to those of a few rodents and other mammals.     

Ultrastructure features of the surface of the gills and the lower pharyngeal jaw of the Tilapia Zilli,redbelly tilapia (Coptodon Zillii,Gervais, 1848)

The present investigation was designed to describe the surface ultrastructure of the gill system of tilapia Zilli. The gill system is formed from four gill arches and each gill arch carries a row of gill filaments on its convex border and two rows of the gill rakers on its concave border. The quadrilateral interbranchial septum has elevated part at the level of the third gill arch. By SEM observations, the gill arch was divided into three regions: rostral, middle and caudal region. The caudal region contained two characteristic structures: oval leaf‐like structure and rounded‐shaped structure. Each oval leaf‐like structure carried two lateral rows of the triangular pointed spines separated by a median groove. All surfaces of gill arches, rakers and filaments were covered with a mosaic of the polygonal pavement cells, in addition to the opening of chloride cells and mucous cells. The gill arch and gill raker had only one appearance of taste buds named type I. Meanwhile, the filaments contained two types of different appearance of the taste buds named: type I and type II. Type I was the main common and similar to that present in gill arch and raker and characterized by its blunt end, while type II had hair‐like structures that projected from the volcano‐shaped depression. The gill rakers were formed from central axis surrounded by two lateral lobulated regions which carry pointed spines, taste buds and the opening of chloride cells. The surface of triangular lower pharyngeal jaw carries numerous teeth‐like papillae which originated from the socket‐like depression.