Developmental Anomalies in Animals

Developmental Anomalies

• Malformations during tissue/organ growth
• Also called congenital diseases
• Present at birth
• Some are genetic (e.g., BOAS, vWD)
• Others not based on genetics (e.g., cerebellar hypoplasia in kittens)
• Examples include polydactyly, palatoschisis, progressive renal atrophy, renal hypoplasia, or cardiac defects

Developmental Anomaly Definitions

Agenesis

• Complete failure of a tissue or organ to grow
• Long-term effects on animal, potentially neonatal death
• Picture shown of MRI of human with cerebellar agenesis, and a normal cerebellum

Aplasia

• Failure of organ formation
• Presence of progenitor cells, but no organization
• Consequences depend on involved organ/tissue
• Bilateral kidney aplasia is lethal
• Refers to failure of tissue to renew itself

Hypoplasia

• Failure of an organ to reach normal size
• Can cause clinical disease in animals
• Severity and life expectancy depend on affected organ and degree of function reduction
• Shown in a picture of hypoplasia of the left lung in a human animal

Adaptive Lesions

• Acquired by an organism in response to homeostasis changes
• Characterized by adaptive cellular responses to physiologic demands
• Lesion is a circumscribed area of pathologic tissue

Hyperplasia

• Increase in organ/tissue size or mass, due to increased cell number
• Only occurs in cells capable of mitotic division
• Often seen concurrently with hypertrophy

Physiologic Hyperplasia

• Tissue/organ size increase in response to normal stimulus (hormonal, etc.)
• Compensatory response
• Example: mammary gland hyperplasia during pregnancy
• Kidney enlargement to compensate for loss of another kidney

Metaplasia

• Adaptive response where one cell type replaces another
• Typically as a response to chronic irritation or hormonal stimulation
• Can progress to dysplasia

Dysplasia

• Abnormal growth, a type of disorderly and atypical hyperplasia
• Loss of normal regular progression from immature to mature cells
• Some types of dysplasia could develop into neoplasia

Hypertrophy

• Increased organ/structure size due to increased cell size, not number
• Picture shows a heart with dilated cardiomyopathy (DCM), a normal heart, and a heart with hypertrophic cardiomyopathy (HCM)

Neoplasia

• New growth of tissue, exceeding normal growth rate/pattern
• Disorganized and persists even after growth stimulus stops
• If unchecked, neoplasia can be lethal

Tumor

• Broadly, any swelling. Now more often used to refer to tumors (masses)
• "Cancer" immediately evokes concerns of death, better to use "mass" or "tumor" when explaining to clients.

Benign Tumor

• Well-differentiated neoplasms
• Do not metastasize (spread)
• Generally do not cause death
• Most pose a quality of life concern (e.g. interference with mobility, eating & drinking, or ulceration)

Malignant Tumor

• Neoplastic growths with variable metastasis (spread) potential
• If left untreated, typically cause death in the effected organism
• Rapid growth, invasive nature
• Variation in cell size, uncontrolled cellular reproduction, loss of cell normal structure/function

Cancer

• Colloquial term for malignant tumor

Classification of Tumors (based on behavior)

Benign

• Localized
• Do not spread
• Amenable to surgical excision

Malignant

• Invade/destroy tissues
• Spread to distant sites
• Not amenable to complete surgical excision
• May cause death

Metastasis

• Greatest threat with malignant neoplasia
• Complex process
• Tumor cells detach, enter bloodstream/lymphatics, penetrate vessel walls, invade tissues
• Carried to lymph nodes, via surgical instruments, etc. (to spread)

Classification of Tumors (based on origin/behavior)

• Tumors are either epithelial (covering tissues) or mesenchymal (connective tissues, muscles) in origin
• Some (more than one tissue) are mixed
• Benign vs. Malignant distinguished by presence of prefix/suffix (e.g., fibroma, sarcoma)

Etiology of Neoplasia

• Causes of tumors are often unknown, but some factors identified include Carcinogens

Zoonotic Disease

• Diseases transmitted between animals and humans
• Some cause minor problems, others severe fatality
• Includes infectious diseases, those caused by prions (e.g. Scrapie, Mad Cow, Chronic wasting disease), etc.

Necropsy

• Thorough post-mortem examination to determine/confirm cause of death
• Performed in two stages—gross necropsy and microscopic necropsy
• Standard steps should be followed

Systemic Evaluations in Necropsy

• Musculoskeletal (muscle mass/skeleton integrity)
• Cardiovascular (blood vessels, heart, valves), including size/position
• Respiratory (trachea/lungs, contents, masses)
• Neurologic (eyes, cranial vault, brain)
• Reproductive (ovaries, uterus, vagina, vulva, mammary glands/prostate, testicles)

This quiz covers various developmental anomalies, including malformations and congenital diseases present at birth. Understand conditions like agenesis, aplasia, and hypoplasia, and their long-term effects on animals. Examples illustrate the critical importance of these anomalies in veterinary medicine.