**5.2.4 More frequently affected systems and selected examples of abnormalities**

*Cardiovascular system*: communication between the pulmonary trunk and the aorta artery (*patent ductus arteriosus,* Fig. 6-A); communication between the atria (*atrial septal defect*) or between the ventricles (*ventricular septal defect*); combination of pulmonary stenosis with a ventricular septal defect, hypertrophy of the right ventricle and an overriding aorta, i.e., the aorta is positioned directly over a ventricular septal defect (*tetratology of Fallot*); imperfect mitral valve and support structures (*mitral dysplasia*); imperfect tricuspid valve and support structures (*tricuspid dysplasia);* right or left atrium divided by a membrane, leaving it with two chambers (*cor triatriatum*); absence of communication between the right atrium and ventricle (*tricuspid atresia*); lack of differentiation of the origins of the pulmonary trunk, aorta and coronary arteries, forming a common arterial trunk (*truncus arteriosus*).

Fig. 6. Examples of abnormalities of the cardiovascular system: A) Patent ductus arteriosus (arrow); B) Abnormality of the caudal vena cava in a dachshund dog with Caroli disease. Note that this vein (raised by forceps) does not have normal morphology. Photograph **B** courtesy of Dr. Marconi R. de Farias, Companion Animal Veterinary Hospital, Faculty of Veterinary Medicine, Pontifícia Universidade Católica do Paraná.

*Musculoskeletal system*: missing jaw (*agnathia*); shorter-than-normal jaw (*brachygnathia*); abnormally small jaw (*micrognathia*); incompletely formed vertebra (*hemivertebra,* Fig. 7-A and B); missing vertebrae in the lumbar and sacral region (*lumbosacral agenesis*); absence of

*Nervous system*: absence of the upper parts of the brain and skull (*anencephaly,* Fig.1-A); retroflection of the head and partial or total absence of the cervical vertebrae associated with serious defects of the central nervous system (*iniencephaly*); stenosis of the aqueduct of Sylvius or another part of the brain's drainage system, leading to accumulated cerebrospinal fluid in the cerebral ventricles (*hydrocephaly*, Fig. 8-A); meningeal herniation, i.e., a protrusion of the meninges at some point of the spine (*meningocele*, Fig. 8-B); meningeal herniation containing a segment of the spinal cord (*meningomyelocele*); meningeal herniation containing part of the brain (*meningoencephalocele*); absence of the major connection between the two cerebral hemispheres (*agenesis of the corpus callosum*); failed development of the prosencephalon (forebrain), compromising the separation of the cerebral hemispheres and causing defects in the midline of the face (*holoprosencephaly*); absence of brain gyri (*lissencephaly*); presence of small and multiple brain gyri (*polymicrogiria*); enlargement of the brain gyri (*pachygiria*); lower than normal development of the cerebellum (*cerebellar* 

Fig. 8. Examples of abnormalities of the central nervous system: A) Hydrocephaly in a dachshund puppy ; B) Meningocele in a newborn Persian kitty; C) Spina bifida occulta with

*Genitourinary System*: missing kidney (*renal agenesis*) that can be unilateral or bilateral; disorganized renal tissue (*renal dysplasia*); cysts in the kidneys (*polycystic renal disease*); fusion of the kidneys by one of the poles, generally the lower, with a silhouette forming in the shape of a horseshoe (*horseshoe kidney*); proximal bifurcation of the renal pelvis (*bifid renal pelvis*); ureter flowing into an organ other than the bladder, commonly in the urethra or the vagina and even the uterus (*ureteral ectopia*); failure to close the urachus (*patent urachus*); urethral opening located on a point of the ventral side of the penis, scrotum or perineum (*hypospadias*, Fig. 9-A); urethra with a connection to the rectum (*urethrorectal fistula*); cystic tumors formed of tissue from different embryonic germ layers that are strangers to the affected organ (*teratoma*). They are more frequent in ovaries and testicles, but can occur in the prostate or in organs from other systems; absence of vagina (vaginal agenesis); larger-than-normal clitoris (*clitoromegaly*, Fig. 9- B); much smaller-than-normal penis (*micropenis*); testicle retained in the abdomen or inguinal canal (*cryptorchidism*), which can be unilateral or bilateral; presence of a membrane that totally or partially closes the vaginal opening (*persistent hymen*); presence of a fibrous ligament between the gland and the foreskin (*persistent penile frenulum*). In domestic mammals, unlike human beings where the hymen and the penile frenulum are characteristics found in adults,

neural involvement in a newborn Rottweiler puppy.

there is a regression of these structures during development.

*hypoplasia*).

the radius (*radial agenesis*, *radial hemimelia*) which may be unilateral or bilateral; absence of one or more limbs (*amelia*); fused digits (*syndactyly*); missing digits and respective metacarpal bones (*ectrodactyly,* Fig. 7-C); existence of extra digits (*polydactyly*); presence of one or more supernumerary limbs (*polymelia*); shorter-than-normal bones due to deficient endochondral ossification (*chondrodysplasia*); incongruence of the elbow joint (*elbow dysplasia*); incongruence of the coxofemoral joint (*hip dysplasia*); congenital joint immobility (*arthrogryposis*); paraumbilical defect in the abdomen with evisceration (*gastroschisis*, Fig. 7- D); congenital umbilical hernia containing viscera (*omphalocele*); congenital cleft of the thoracic wall (*thoracoschisis*), with exteriorization of the heart (*ectopia cordis*).

Fig. 7. Examples of abnormalities of the musculoskeletal system: A) Newborn foal with serious scoliosis as a result of spinal defects (hemivertebrae); B) Radiograph of the foal shown in A, revealing the hemivertebrae (arrow); C) Ectrodactyly in a poodle dog (left thoracic limb); D) Gastroschisis in a newborn Siberian husky; E) Pituitary dwarfism in a German shepherd at the age of 4 years; F) Duplication of the left hind paw of a newborn Rottweiler (polypodia). Photographs **A** and **B** courtesy of Dr. Pedro V. Michelloto Junior, Equine Veterinary Hospital, Faculty of Veterinary Medicine, Pontifícia Universidade Católica do Paraná.

the radius (*radial agenesis*, *radial hemimelia*) which may be unilateral or bilateral; absence of one or more limbs (*amelia*); fused digits (*syndactyly*); missing digits and respective metacarpal bones (*ectrodactyly,* Fig. 7-C); existence of extra digits (*polydactyly*); presence of one or more supernumerary limbs (*polymelia*); shorter-than-normal bones due to deficient endochondral ossification (*chondrodysplasia*); incongruence of the elbow joint (*elbow dysplasia*); incongruence of the coxofemoral joint (*hip dysplasia*); congenital joint immobility (*arthrogryposis*); paraumbilical defect in the abdomen with evisceration (*gastroschisis*, Fig. 7- D); congenital umbilical hernia containing viscera (*omphalocele*); congenital cleft of the

thoracic wall (*thoracoschisis*), with exteriorization of the heart (*ectopia cordis*).

Fig. 7. Examples of abnormalities of the musculoskeletal system: A) Newborn foal with serious scoliosis as a result of spinal defects (hemivertebrae); B) Radiograph of the foal shown in A, revealing the hemivertebrae (arrow); C) Ectrodactyly in a poodle dog (left thoracic limb); D) Gastroschisis in a newborn Siberian husky; E) Pituitary dwarfism in a German shepherd at the age of 4 years; F) Duplication of the left hind paw of a newborn Rottweiler (polypodia). Photographs **A** and **B** courtesy of Dr. Pedro V. Michelloto Junior, Equine Veterinary Hospital, Faculty of Veterinary Medicine, Pontifícia Universidade

Católica do Paraná.

*Nervous system*: absence of the upper parts of the brain and skull (*anencephaly,* Fig.1-A); retroflection of the head and partial or total absence of the cervical vertebrae associated with serious defects of the central nervous system (*iniencephaly*); stenosis of the aqueduct of Sylvius or another part of the brain's drainage system, leading to accumulated cerebrospinal fluid in the cerebral ventricles (*hydrocephaly*, Fig. 8-A); meningeal herniation, i.e., a protrusion of the meninges at some point of the spine (*meningocele*, Fig. 8-B); meningeal herniation containing a segment of the spinal cord (*meningomyelocele*); meningeal herniation containing part of the brain (*meningoencephalocele*); absence of the major connection between the two cerebral hemispheres (*agenesis of the corpus callosum*); failed development of the prosencephalon (forebrain), compromising the separation of the cerebral hemispheres and causing defects in the midline of the face (*holoprosencephaly*); absence of brain gyri (*lissencephaly*); presence of small and multiple brain gyri (*polymicrogiria*); enlargement of the brain gyri (*pachygiria*); lower than normal development of the cerebellum (*cerebellar hypoplasia*).

Fig. 8. Examples of abnormalities of the central nervous system: A) Hydrocephaly in a dachshund puppy ; B) Meningocele in a newborn Persian kitty; C) Spina bifida occulta with neural involvement in a newborn Rottweiler puppy.

*Genitourinary System*: missing kidney (*renal agenesis*) that can be unilateral or bilateral; disorganized renal tissue (*renal dysplasia*); cysts in the kidneys (*polycystic renal disease*); fusion of the kidneys by one of the poles, generally the lower, with a silhouette forming in the shape of a horseshoe (*horseshoe kidney*); proximal bifurcation of the renal pelvis (*bifid renal pelvis*); ureter flowing into an organ other than the bladder, commonly in the urethra or the vagina and even the uterus (*ureteral ectopia*); failure to close the urachus (*patent urachus*); urethral opening located on a point of the ventral side of the penis, scrotum or perineum (*hypospadias*, Fig. 9-A); urethra with a connection to the rectum (*urethrorectal fistula*); cystic tumors formed of tissue from different embryonic germ layers that are strangers to the affected organ (*teratoma*). They are more frequent in ovaries and testicles, but can occur in the prostate or in organs from other systems; absence of vagina (vaginal agenesis); larger-than-normal clitoris (*clitoromegaly*, Fig. 9- B); much smaller-than-normal penis (*micropenis*); testicle retained in the abdomen or inguinal canal (*cryptorchidism*), which can be unilateral or bilateral; presence of a membrane that totally or partially closes the vaginal opening (*persistent hymen*); presence of a fibrous ligament between the gland and the foreskin (*persistent penile frenulum*). In domestic mammals, unlike human beings where the hymen and the penile frenulum are characteristics found in adults, there is a regression of these structures during development.

speaking, however, the cause is not always known, but it is presumed. Generally, syndromes are considered as having resulted from a disorder in more than one developmental field (Spranger, 1982). Examples: 1) Hurler Syndrome (mucopolysaccharidosis I), a recessive autosomal syndrome in which there is a deficiency of alpha-L-iduronidase. Affected dogs have corneal opacity, facial dysmorphism, joint abnormalities, aortic dilation and thickened heart valves (Traas et al., 2007); 2) Hunter Syndrome (mucopolysaccharidosis II), an X-linked recessive syndrome in which there is iduronate-sulfatase deficiency. Affected dogs have a course facial appearance,

macrodactyly, corneal dystrophy and neurological alterations (Wilkerson, 1998).

Fig. 10. Examples of single defect: A) Dog with cleft palate; B) Eyelid coloboma (arrow) in a cat; C) Example of a multiple congenital anomaly in a dog (meningocele and peromelia).

Developmental field defects are resulting from a *dysmorphogenetic response* of a developmental field (Hersch et al., 2002) and are causally heterogeneous. This means that the *same field reacts in a similar way to different factors*. They may be multiple anomalies that affect an area of anatomically related structures, being monotopic field defects; or they may be anomalies in different areas of the body, being polytopic field defects. Holoprosencephaly in its different degrees is a monotopic field, such as semilobar holoprosencephaly in Morgan horses (Kock et al., 2005), and may be associated with otocephaly, as reported by Martínez et al., (2006) in a Rottweiler dog. Lumbosacral agenesis in its different degrees is a polytopic field defect and has been described in a number of domestic species, such as sheep (Denis, 1975), cattle (Jones, 1999; Son et al., 2008), pigs

Association is a *combination of two or more defects* in the same individual and occurs in the population more frequently than could be expected merely at random, but it does *not have a specific cause*. Like syndromes, associations must be defects involving more than one developmental field (or only one polytopic field), but are etiologically heterogeneous.

**6.2.2 Developmental field defects** 

**6.2.3 Association** 

(Avedillo & Camón, 2007) and dogs (Araújo et al., 2008).

Fig. 9. Examples of abnormalities of the genitourinary system: A) Perineal hypospadias in a dog. Observe the urethral opening (arrow) located in the perineum, near the anus; B) Ambiguous genitalia in a dog with XX true hermaphroditism.
