Module 1: Pituitary Pathology and Pathophysiology

Question 1

The anterior pituitary (adenohypophysis) is composed of two histologically and functionally distinct regions:

Answer 1

the pars distalis and the pars intermedia

Question 2

there are three morphologically distinct cells within the pars distalis:

Answer 2

acidophils, basophils, and chromophobes

Question 3

it lacks the secretory polygonal cells characteristic of the anterior pituitary

Answer 3

posterior pituitary, or pars nervosa

Question 4

Are transported along the axons into the pars nervosa where they are secreted and enter the bloodstream

Answer 4

anti-diuretic hormone (ADH; also referred to as vasopressin) and oxytocin

Question 5

specialized supporting cells (glial cells) of the pars nervosa that surround the axons and facilitate secretion of ADH and oxytocin

Answer 5

Pituicytes

Question 6

is composed predominantly of anuclear (without nuclei) axons and small capillaries, scattered nuclei are apparent within the neuropil; these are pituicytes

Answer 6

pars nervosa

Question 7

What are the clinical disease of functional neoplasms?

Answer 7

effects of overproduction
of trophic hormones +/- expansile or infiltrative effects

Question 8

What are the clinical disease of Non-functional neoplasms?

Answer 8

expansile or
infiltrative effects (tissue loss/destruction)

Question 9

What are the Clinical Signs of Equine pituitary pars intermedia dysfunction (PPID)?

Answer 9

Clinical signs primarily due to compression of normal
pituitary/hypothalamus (although some increased ACTH, POMC, MSH,
β-END)
Not really a functional tumor

Question 10

• Develop in older horses (females>males)
• Clinical signs
• PU/PD
• Polyphagia
• Hirsutism (hairy coat)
• Laminitis
• Muscle weakness/atrophy
• Hyperhidrosis
• May develop insulin-resistant hyperglycemia
• Diabetes insipidus

Answer 10

PPID (Equine pituitary pars intermedia dysfunction)

Question 11

Most of Pituitary tumors in domestic animals are ________

Answer 11

Benign

Question 12

• Clinical signs primarily due to effects of cortisol excess
• Common in dogs (less common in cats)
• Size does not correlate with functional activity
• Bilateral adrenal cortical hyperplasia

Answer 12

ACTH-secreting adenomas (pars distalis&raquo_space;> pars intermedia)
Functional tumor

Question 13

• Clinical signs primarily due to cortisol excess (adrenal cortisol
hypersecretion)

• Polyuric/polydipsic
• Symmetric alopecia (truncal)
• Pot-bellied appearance – loss of abdominal musculature
• Calcinosis cutis – mineralization of dermal collagen
• Hypercoagulability (pulmonary thromboemboli)

Answer 13

Canine Cushing’s disease
(Pituitary adenoma of the pars distalis (80%))

Question 14

• Most commonly prolactin-secreting adenomas
• Prolactin may induce mammary neoplasia in rats
• Associated with mammary fibroadenomas – benign mammary tumors

Answer 14

Pituitary adenoma of the pars distalis in Rats

Question 15

Pituitary adenomas and mammary tumors in rats are associated with
increased _______________

Answer 15

caloric intake

Question 16

• Pituitary tumors are common in this species
• Neurological signs (ataxia, difficulty
flying, head tilt, abnormal molting)
• Growth hormone secreting
• Many are malignant and may metastasize

Answer 16

Pituitary adenomas in Budgerigars (parakeets)

Question 17

• Uncommon
• Primarily prolactin-secreting
• Frequently clinically asymptomatic

Answer 17

Pituitary adenomas in Cynomolgus macaques

Question 18

when you have a short supply (deficiency) of one or more of the pituitary hormones

Answer 18

Hypopituitarism

Question 19

Hypopituitarism
• Two basic pathogeneses:

Answer 19

• Congenital absence (primary hypopituitarism)
• Acquired destruction of pituitary (secondary hypopituitarism)

Question 20

• Rare diseases (mostly canine)
• Juvenile animals affected

Answer 20

primary hypopituitarism

Question 21

• Neoplasia (primary vs. metastatic)
• Pituitary abscesses

Answer 21

secondary hypopituitarism

Question 22

• Autosomal recessive inheritance in German shepherd dog, Karelian
bear dog, Spitz, et al
• DNA repeat of intron 5 of LHX3 gene
• Failure of Rathke’s pouch to differentiate into the pars distalis
• Abnormal development leads to cyst formation →expansile mass and
compression/destruction of remaining functional pituitary tissue

Answer 22

Primary hypopituitarism (Juvenile-onset panhypopituitarism,
piutuitary dwarfism)

Question 23

• Clinical appearance
• Major clinical signs associated with reduced/absence of:
• Growth hormone (GH)
• Thyroid stimulating hormone (TSH)
• Adrenocorticotrophic hormone (ACTH)
• Gonadotrophic hormones (LH, FSH)
• Key point: Without upstream stimulation by the pituitary gland’s trophic hormones, there is reduced production of the downstream hormones (i.e. thyroxine, somatomedin, cortisol, sex hormones)
• Affected dogs have small stature, lack guard hairs (puppy coat), significantly delayed physeal closure, alopecia, atrophic skin, etc.
• Diagnostic test for insulin-like growth factor (somatomedin) is available (MSU VDL)

Answer 23

Juvenile-onset hypopituitarism

Question 24

• Acquired loss of pituitary function
• Infectious
• Pituitary abscess
• Cattle, small ruminants
• Clinical signs dependent on degree of pituitary destruction +/-
compression/destruction of regional brain (may be acute or chronic)
• Hematogenous spread&raquo_space; regional extension
• Uncommonly, may be associated with skull fracture/penetrating wound, otitis media,
or tooth root abscess

Answer 24

Secondary hypopituitarism

Question 25

• Primary non-functional pituitary neoplasms
• Suprasellar germ cell tumors and craniopharyngiomas
• Rare
• Frequently affect younger dogs than other pituitary/brain neoplasms
• Disease is due to expansile effects (neurological signs)
• Metastatic neoplasia (adult onset hypopituitarism)
• Lymphoma, melanoma, hemangiosarcoma, carcinoma
• In general, neurological signs due to tumor infiltration
predominate over pituitary-specific signs

Answer 25

Secondary hypopituitarism

Question 26

What is the most likely autopsy finding in a 7 month-old MN German shepherd dog with pituitary dwarfism?

Answer 26

Pituitary Cyst

Question 27

Dogs with pituitary adenomas may present with ___________________ signs

Answer 27

primary neurological