Lecture 83: Gastrointestinal pathology

Normal GI mucosa appearance

Smooth and shiny serosal and mucosal surfaces; exception: rumen papillae (rough, dull).

GALT - definition

Gut-associated lymphoid tissue; 25% of total lymphoid mass; includes lamina propria and organized lymphoid tissue.

GALT - function

Monitors for pathogens while avoiding false alarms; supports crypt cell differentiation.

Diarrhea - definition

Abnormally fluid feces with increased volume and frequency of defecation.

Diarrhea - pathogen categories

Induce secretion, induce inflammation, or are invasive (e.g., Salmonella).

Noninflammatory diarrhea

Disrupts absorption/secretion without cell destruction; no inflammation.

Inflammatory diarrhea

Caused by cytotoxins or invasive organisms; triggers cytokines and inflammation.

Villous enterocyte pathogens

Rotavirus, enteric coronavirus, TGEV, Brachyspira, coccidia, cryptosporidium.

Villous enterocyte loss

Leads to maldigestion and malabsorption; fermentation increases osmolality and fluid content.

Crypt cell loss - consequences

Impaired regeneration; delayed clinical signs; often fatal; e.g., parvovirus, BVDV, rinderpest.

Crypt cell pathogens

Parvoviruses, BVDV, rinderpest, vomitoxin; target mitotic cells in crypts.

Intestinal defense mechanisms

Microbiota, secretions, acidity, motility, epithelial turnover, bile salts, immune responses.

Achlorhydria - neonates

Young animals lack gastric acid; ↑ susceptibility to pathogens like E. coli.

Cleft palate - definition

Palatoschisis; failure of palate fusion; may be genetic or toxic in origin.

Cleft lip - definition

Cheiloschisis; failure of upper lip fusion; "hare lip"; normal in rabbits.

Cleft palate - consequences

Starvation (poor suckling), aspiration pneumonia (oral-nasal communication).

Thrush - cause

Candida spp. overgrowth due to antibiotics, hyperglycemia, or immunosuppression.

Vesicular stomatitides - cause

Viral cytolysis → vesicle formation → rupture → erosions/ulcers; not fatal but economically significant.

Vesicular stomatitides - lesions

Fluid-filled vesicles on lips, tongue, palate, planum nasale; hyperemic ulcers post-rupture.

Foreign body - oral cavity

Feed in mouth postmortem = abnormal (except ruminants); suggests dysphagia or CNS disease.

Foreign body stomatitis - dogs

Plant fibers, burrs, quills; gingivitis, ulcers, granulomas with embedded material.

Foreign body - ruminants

Grass seeds/awns exacerbate periodontitis; may lead to osteomyelitis.

Foreign body - horses

Dry triticale hay → oral ulceration; awns embedded in mucosa.

Foreign body - swine

Pharyngeal diverticulum traps awns → cellulitis; similar lesions in sheep/cattle from drenching/balling guns.

Feline calicivirus - oral lesions

Vesicles → ulcers on tongue, hard palate; worse with dry food; may co-infect with herpesvirus.

Feline stomatitis - definition

Chronic ulcerative inflammation of fauces, palate, gingiva, tongue; often older cats.

Feline stomatitis - etiology

Multifactorial; microbiota imbalance, calicivirus, herpesvirus, FeLV, FIV.

Lymphoplasmacytic stomatitis

Chronic idiopathic inflammation; red gums, fetid breath, inappetence; lymphocyte/plasma cell infiltrate.

Feline plasma cell gingivitis

Proliferative red lesions in glossopalatine arches; polyclonal gammopathy; immune-mediated.

Eosinophilic ulcer - cats

Chronic ulcer at lip margin; red-brown, well-demarcated; part of eosinophilic granuloma complex.

Eosinophilic ulcer - etiology

Unknown; suspected allergy or eosinophil dysfunction; responds to steroids but recurs.

Uremic stomatitis - dogs/cats

Gray-brown ulcers on tongue, gums, lips; ammonia from urea + urease bacteria damages mucosa.

Uremic stomatitis - pigs

Part of greasy pig disease; ulcers on tongue and palate in preweaning piglets.

Tonsillar tumors - dogs

Lymphosarcoma, SCC; bilateral soft pale tonsils in lymphoma; may precede lymphadenopathy.

Dysphagia - oral causes

Stomatitis, glossitis, gingivitis, cleft palate, hypoglossal nerve dysfunction.

Dysphagia - pharyngeal causes

Pharyngitis, tonsillar masses, guttural pouch disease, encephalitis, myasthenia gravis.

Oral fibrous hyperplasia

Dogs; focal or diffuse gingival overgrowth; may cover crown; linked to chronic inflammation.

Oral neoplasia - prevalence

6% of canine, 7% of feline tumors; SCC, fibrosarcoma, melanoma most common.

Oral neoplasia - signs

Drooling, halitosis, pain, dysphagia, weight loss, loose teeth, bleeding, voice change.

Oral neoplasia - prognosis

Poor unless resected early; rapid progression and local invasion common.

Canine oral tumors

70% of alimentary tumors in oral cavity; SCC, melanoma, fibrosarcoma dominate.

SCC - cats

Ventral tongue near frenulum most common; gingiva second; often mistaken for gingivitis.

SCC - cats - behavior

Locally invasive; bone invasion common; low metastasis; poor surgical prognosis.

SCC - dogs

Tonsils and gums most common; early metastasis to lymph nodes and lungs.

SCC - horses

Slow-growing, destructive; gums/palate; invade sinuses, orbit, cranial cavity.

Melanomas - dogs

90% malignant; black or amelanotic; invade bone; >70% metastasize to lymph nodes.

Melanomas - metastasis

Lymphatic and hematogenous spread; lungs common; poor prognosis even with surgery.

Fibrosarcoma - dogs

15-25% of oral tumors; young large breeds; maxilla, palate, mandible; bone invasion common.

Fibrosarcoma - cats

Second most common oral malignancy; gingiva and palate; resembles canine tumor.

Oral SCC - cats

Most common oral malignancy; ventral tongue near frenulum; gingiva second most common site.

Oral SCC - cats - presentation

Advanced at diagnosis; locally invasive into bone; low metastasis; poor prognosis.

Oral SCC - cats - gross appearance

Irregular, nodular, red-gray, friable, ulcerated, bleeds easily.

Oral SCC - dogs

Second most common oral malignancy; tonsils and gums most affected; lips/tongue less common.

Tonsillar SCC - dogs

Unilateral; early lesion = granular plaque; advanced = enlarged, nodular, ulcerated tonsil.

Tonsillar SCC - metastasis

Early spread to retropharyngeal nodes, thyroid, lungs, bone; differentiate from lymphoma.

Gingival SCC - dogs

May be linked to chronic periodontitis; unclear if cause or consequence.

Oral SCC - horses

Rare; gums/palate; slow-growing but destructive; invade sinuses, orbit, cranial cavity.

Oral SCC - cattle

Very rare; not a common oral malignancy.

Oral melanoma - dogs

90% malignant; black or amelanotic; neural crest origin; aggressive and invasive.

Oral melanoma - metastasis

Lymphatic and hematogenous spread; lungs common; poor prognosis even with treatment.

Oral melanoma - survival

Median survival untreated = 2 months; post-treatment ~3 months; no metastasis = ~8 months.

Oral fibrosarcoma - dogs

15-25% of oral tumors; most common oral sarcoma; young large breeds predisposed.

Oral fibrosarcoma - dogs - sites

Maxilla, palate, rostral mandible; less often buccal mucosa, lips, tongue.

Oral fibrosarcoma - dogs - behavior

Locally invasive; bone destruction; recurrence common; metastasis to nodes/lungs possible.

Oral fibrosarcoma - cats

Second most common oral malignancy; resembles canine tumor; bone invasion common.

Canine oral papillomatosis

Papovavirus-induced; <1 year old; white, friable, papilliform lesions; regress spontaneously.

Oral papillomas - features

Multiple, white-gray, pedunculated, keratinized surface; long-lasting immunity post-infection.

Oral extramedullary plasmacytoma

Slow-growing; non-invasive; no metastasis; occurs in oral mucosa, esophagus, intestine.

Oral fibrosarcoma - histology

May appear benign histologically but behave aggressively; especially in large-breed dogs.

Oral SCC - paraneoplastic signs

Hypercalcemia reported; may complicate prognosis and management.

Oral neoplasia - clinical signs

Drooling, halitosis, pain, dysphagia, anorexia, weight loss, bleeding, loose teeth, voice change.