Cat Anatomy: A Visual Guide to Organs and Body Systems
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Feline-specific anatomical differences from the dog that matter clinically: drug metabolism pathways (glucuronidation deficiency), surgical landmarks, unique features (clavicle, supracondylar foramen, retractable claws), and the organ systems where cats are not small dogs.
- Cats are obligate carnivores — their hepatic glucuronidation capacity is genetically limited (pseudogenised UGT1A6), making them exquisitely sensitive to drugs metabolised by glucuronidation: paracetamol (acetaminophen), aspirin, propofol (with repeated dosing), and phenolic compounds.
- The feline scapula has three processes (acromion, hamate, suprahamate) — a unique feature among domestic mammals. The clavicle is a tiny, free-floating ossicle in the clavicular tendon — not a fracture.
- The feline humerus has a supracondylar foramen (medial) transmitting the median nerve and brachial vessels. This is absent in the dog. A distal humeral fracture that compromises this foramen can cause median nerve entrapment.
- Cats have retractable claws on all digits (digit I–V on the forelimb; I–IV on the hindlimb; digit I of the hindlimb is usually absent). The deep digital flexor tendon maintains claw retraction at rest; active extension of the digital extensors protracts the claw.
- The feline kidney is more caudal than the canine kidney, and the feline urethra is much more resistant to catheterisation. Never force a urinary catheter in a cat — the urethra is easily torn, especially at the pre-prostatic narrowing in males.
- A cat that has received paracetamol (acetaminophen) — even a single tablet — is a toxicological emergency. Cats cannot glucuronidate paracetamol; the toxic metabolite NAPQI accumulates, causing methaemoglobinaemia and hepatic necrosis. Treat with N-acetylcysteine and S-adenosylmethionine (SAMe) within hours of ingestion.
- A cat with acute pelvic limb paresis and a cold, pulseless pelvic limb has an aortic thromboembolism (ATE, 'saddle thrombus') until proven otherwise. This is the most common presentation of feline hypertrophic cardiomyopathy (HCM). Time to reperfusion is measured in hours — beyond 6 hours, the prognosis for limb salvage is guarded.
- A male cat with repeated, unproductive straining in the litter box has a urethral obstruction until proven otherwise. Palpate the bladder — if it is large, firm, and painful, the cat is obstructed. Urethral obstruction causes hyperkalaemia and metabolic acidosis; death can occur within 24–48 hours from cardiac arrhythmia. Relieve the obstruction immediately.
- A cat that has not eaten for >48–72 hours is at risk for hepatic lipidosis — especially if the cat was previously obese. Cats have a limited capacity to mobilise peripheral fat stores without hepatic lipid accumulation, and prolonged anorexia triggers a cascade that can lead to fatal hepatic failure. Early enteral nutrition (via naso-oesophageal or oesophagostomy tube) is life-saving.
Cats Are Not Small Dogs: The Clinical Significance of Feline Anatomical Differences
The domestic cat (Felis catus) shares the same body plan as the dog — it is a digitigrade, cursorial carnivore with the same organ systems and the same vertebral formula (C7, T13, L7, S3, Cd18–20). But the differences — in drug metabolism, surgical anatomy, and breed-specific pathology — are profound enough that treating a cat as a 'small dog' leads to iatrogenic harm with alarming regularity. This article focuses exclusively on those differences.
| System | Canine Feature | Feline Difference | Clinical Consequence |
|---|---|---|---|
| Hepatic metabolism | Full glucuronidation capacity (UGT1A6 functional) | UGT1A6 pseudogenised — severely impaired glucuronidation of phenolic compounds | Paracetamol, aspirin, propofol (repeated doses), carprofen, and some opioids (morphine undergoes glucuronidation — use buprenorphine or methadone instead in cats) |
| Clavicle | Absent (reduced to a fibrous intersection in the brachiocephalicus) | Present as a tiny (2–3 mm) ossicle in the clavicular tendon — the clavicular remnant | The clavicle is normal — it is not a fracture fragment on thoracic radiographs. The cat's shoulder girdle has slightly more stability than the dog's because of this remnant |
| Scapula | Acromion process only | Acromion, hamate, and suprahamate processes — three distinct processes | These are palpable landmarks for shoulder examination. The suprahamate process is the origin of the teres major muscle |
| Humerus | No supracondylar foramen | Supracondylar foramen (medial distal humerus) transmits the median nerve + brachial vessels | A distal humeral fracture at this site can entrap the median nerve. The foramen is visible on a craniocaudal radiograph as a radiolucent circle in the medial supracondylar region — do not mistake it for a lytic lesion |
| Claws | Non-retractable; the DDFT and digital extensors balance claw position | Retractable on all digits (forelimb I–V, hindlimb I–IV); the DDFT passively maintains retraction; active extension protracts the claw | Declawing (onychectomy) is an amputation of the distal phalanx (P3) — it is not a 'nail removal.' It is banned in many jurisdictions. A cat that is declawed has chronic pain and altered gait because P3 is the weight-bearing digit bone |
Drug Metabolism: The Feline Glucuronidation Deficiency
The single most clinically significant anatomical difference between cats and dogs is not visible on dissection — it is a molecular defect in hepatic glucuronidation. Glucuronidation is one of the two major phase II conjugation pathways (alongside sulfation) that render lipid-soluble drugs and toxins water-soluble for renal excretion. In cats, the gene encoding UDP-glucuronosyltransferase 1A6 (UGT1A6) — the isoform responsible for conjugating phenolic compounds — is pseudogenised: it contains multiple mutations that render it non-functional.
This means that cats cannot efficiently glucuronidate phenolic drugs and toxins, including:
- Paracetamol (acetaminophen): The toxic metabolite NAPQI (N-acetyl-p-benzoquinone imine) cannot be conjugated and detoxified. NAPQI causes oxidative injury to erythrocytes (Heinz body anaemia, methaemoglobinaemia) and hepatocytes (centrilobular necrosis). A single 325 mg tablet can be fatal to a cat.
- Aspirin (acetylsalicylic acid): Cats glucuronidate aspirin slowly, resulting in a prolonged half-life (38 hours in cats vs 7–8 hours in dogs). Chronic dosing leads to salicylate toxicity (acidosis, gastric ulceration, bone marrow suppression).
- Propofol: The phenolic metabolite of propofol requires glucuronidation for excretion. Single-dose induction is safe; however, prolonged infusion (TIVA) for >30–60 minutes or repeated daily dosing causes Heinz body anaemia in cats. Alfaxalone is a safer alternative for maintenance.
- Carprofen: An NSAID that undergoes extensive glucuronidation. Carprofen has been associated with idiosyncratic hepatotoxicity in some dogs, but in cats, the impaired glucuronidation makes chronic dosing particularly risky. Meloxicam (primarily oxidised, not glucuronidated) is safer for chronic feline use.
- Morphine: Morphine-6-glucuronide is an active metabolite responsible for much of morphine's analgesic effect. Cats produce less M6G than dogs, making morphine less effective as an analgesic. Buprenorphine, methadone, or fentanyl are preferred opioids in the cat.
| Drug | Feline Half-Life | Canine Half-Life | Safe in Cats? | Alternative if Contraindicated |
|---|---|---|---|---|
| Paracetamol | Undefined (toxic at any dose) | 1–3 hours | NEVER — fatal at 10–50 mg/kg | No safe alternative — use opioids (buprenorphine) for analgesia; no antipyretic is safe in cats except dipyrone (metamizole) in some countries |
| Aspirin | 38 hours | 7–8 hours | Only at 10 mg/kg q48–72h (not q12h like dogs) | Meloxicam (low dose, 0.05 mg/kg q24h, maximum 4 days in some countries); robenacoxib (feline-licensed COX-2 selective NSAID) |
| Propofol | ~30 min (single dose); accumulates with repeated doses | ~25 min (no accumulation) | Safe for single-dose induction; avoid TIVA and repeated daily dosing | Alfaxalone (no phenolic metabolite; safe for TIVA); etomidate (if cardiovascular compromise) |
| Carprofen | Prolonged (not well studied) | 8–12 hours | Not recommended for chronic use; single perioperative dose may be acceptable | Meloxicam; robenacoxib |
| Morphine | ~1 hour (reduced M6G production) | ~1 hour (with active M6G metabolite) | Safe but less effective; use with caution (histamine release → vomiting) | Buprenorphine (high-affinity partial μ-agonist; excellent feline analgesic); methadone (full μ-agonist, NMDA antagonist) |
The Feline Musculoskeletal System: Unique Features
The feline musculoskeletal system shares the digitigrade stance and cursorial adaptations of the dog but with several unique features that reflect the cat's hunting style — ambush predation with explosive acceleration, vertical leaping, and climbing.
| Structure | Feline Feature | Canine Comparison | Clinical Significance |
|---|---|---|---|
| Scapula | Three processes: acromion, hamate, suprahamate | Acromion only (smaller) | The suprahamate process is palpable as a dorsal prominence cranial to the shoulder joint. It can be avulsed in trauma (rare) and is a landmark for scapular fractures |
| Clavicle | Tiny (2–3 mm) ossicle in the clavicular tendon | Absent (fibrous intersection only) | Visible on thoracic radiographs — do not mistake for a foreign body or fracture fragment. It provides minimal but real added stability to the shoulder girdle, contributing to the cat's ability to squeeze through narrow spaces |
| Humerus | Supracondylar foramen (medial) | Absent | Transmits the median nerve + brachial vessels. A distal humeral fracture at this site can cause median nerve entrapment with loss of flexion of the carpus and digits — this is a surgical emergency requiring nerve decompression |
| Radius/Ulna | Separate; more mobile than in the dog | Separate; limited pronation/supination | Cats have slightly more pronation/supination than dogs, which assists in climbing and grasping prey. A fracture of one bone (especially the radius) in a cat may heal without fixation of the second bone if the interosseous membrane is intact, because the bones can still align properly |
| Pelvis | Narrower than the dog; ilial wings are smaller; the pelvic canal is narrower in males | Broader; larger ilial wings; the pelvic canal is wider in both sexes | The narrow pelvic canal in male cats predisposes to urethral obstruction (the pelvic urethra is compressed by the narrow canal) and makes pelvic fracture repair more technically demanding. In female cats, the pelvic canal is wider, and obstetrical problems are less common than in dogs |
| Patella | Small, ovoid | Larger, triangular | Patellar luxation is less common in cats than in dogs. When it occurs, it is typically medial and may be associated with hip dysplasia (which is underdiagnosed in cats because they mask lameness well) |
The Feline Gastrointestinal System: An Obligate Carnivore's Tract
The cat is an obligate carnivore — unlike the dog, which is a facultative carnivore-omnivore. This means that cats have specific metabolic requirements (taurine, arginine, arachidonic acid, preformed vitamin A) that must be supplied in the diet, and their GI tract is shorter and more simplified than the dog's.
| Segment | Feline-Feature | Canine Comparison | Clinical Significance |
|---|---|---|---|
| Tongue | Filiform papillae are heavily keratinised, forming posteriorly-directed spines ('papillae conicae') | Filiform papillae are softer and less keratinised | The feline tongue is a grooming tool and a rasp for stripping meat from bones. The keratinised papillae can trap linear foreign bodies (thread, string) — the cat cannot spit them out. A linear foreign body anchored under the tongue is pathognomonic for a GI linear foreign body. Always check under the tongue of a vomiting cat. |
| Oesophagus | Distal third is smooth muscle (like humans); proximal two-thirds is striated muscle | Entire oesophagus is striated muscle (unique to dogs and ruminants) | Diseases affecting striated muscle (myasthenia gravis, polymyositis) cause megaesophagus in the dog but only affect the proximal two-thirds in the cat. The distal smooth-muscle segment may remain functional, resulting in segmental megaesophagus |
| Pancreatic duct | Only one duct — the pancreatic duct — which joins the common bile duct at the major duodenal papilla. The accessory pancreatic duct is ABSENT | Two ducts: accessory pancreatic duct (minor papilla — the larger one in dogs) and pancreatic duct (major papilla) | Biliary obstruction in a cat also obstructs the pancreas (because the common bile duct and pancreatic duct merge). Pancreatitis and cholangitis often occur together (feline triaditis: pancreatitis + cholangiohepatitis + inflammatory bowel disease) |
| Pancreas | Right and left lobes, connected by a body; the right lobe is within the mesoduodenum (same as dog) | Same gross anatomy | Feline pancreatitis is often more severe than canine pancreatitis and has a higher mortality rate. The disease is often idiopathic and may be associated with concurrent hepatic lipidosis and cholangitis (triaditis) |
| Cecum | Small, comma-shaped; ~2–4 cm long | Similar size; more coiled shape | The feline cecum is a common site for a 'cecal inversion' (intussusception) — a rare cause of chronic diarrhoea. Palpation or ultrasound reveals a sausage-shaped mass in the right hemiabdomen |
| Colon | Shorter than the dog (proportionally); the descending colon is more dorsal | Similar anatomy; ~40–60 cm (medium dog) | Megacolon is far more common in cats than dogs — especially in middle-aged, indoor, overweight cats with chronic obstipation. The colon loses contractility and becomes a dilated, flaccid sac. Subtotal colectomy (removal of 90–95 % of the colon with ileocolic or colocolonic anastomosis) is often curative |
The Feline Urogenital System: Kidneys, Ureters, and the Unique Male Urethra
The feline urinary system is anatomically similar to the dog's — two retroperitoneal kidneys (the right is slightly more cranial), two ureters, a urinary bladder, and a urethra. However, the feline kidney is positioned more caudally (L1–L4, compared to T13–L3 in the dog), and — most importantly — the male feline urethra is exquisitely narrow and easily obstructed.
| Structure | Feline Feature | Canine Comparison | Clinical Significance |
|---|---|---|---|
| Kidneys | More caudal (L1–L4); the right kidney is not in a distinct renal fossa (unlike the dog) | T13–L3; right kidney in the renal fossa of the caudate liver lobe | The feline kidneys are more palpable (more caudal = more accessible). Feline chronic kidney disease (CKD) is the most common geriatric feline disease — the kidneys become small, irregular, and firm on palpation. Renal size is a key prognostic indicator |
| Ureters | Similar anatomy; cross the external iliac arteries ventrally at the pelvic brim | Same | Feline ureterolithiasis is increasing in prevalence (possibly due to dietary factors). Ureteral obstruction (partial or complete) causes hydronephrosis. Subcutaneous ureteral bypass (SUB) devices are increasingly used in cats because ureteral surgery is technically very difficult in this species |
| Male urethra | Long, narrow, with two 90° bends: (1) at the ischial arch, where the urethra turns from the pelvic to the penile portion, and (2) at the glans penis. The penile urethra is extremely narrow (<0.5 mm diameter at the tip in a 5 kg cat) | Wider and straighter; the os penis is the narrowest point, but it is still wider than the feline penile urethra | Feline urethral obstruction (FUO) is one of the most common feline emergencies — typically caused by a urethral plug (proteinaceous matrix + struvite crystals) in male, indoor, overweight, dry-food-fed cats. The obstruction occurs at the penile urethra. Catheterisation requires extreme gentleness — a 3.5–5 Fr open-ended catheter is advanced through the obstruction. NEVER force a catheter: urethral rupture causes uroabdomen and is often fatal |
| Female urethra | Short, wide, opens on the ventral floor of the vestibule | Similar; wider than the male urethra | Female cats rarely obstruct. Urethral sphincter mechanism incompetence (USMI) — common in spayed female dogs — is extremely rare in spayed female cats |
| Prostate | The cat has a prostate (like the dog) — it is located at the bladder neck but is small and rarely diseased | Same location; commonly diseased (BPH, prostatitis, abscess, neoplasia) | Prostatic disease is rare in cats. If the prostate is enlarged, consider prostatic neoplasia (prostatic adenocarcinoma is aggressive in cats and has usually metastasised by the time of diagnosis) |
Feline lower urinary tract disease (FLUTD) is a syndrome, not a disease. The three most common causes are: (1) feline idiopathic cystitis (FIC — stress-induced neurogenic inflammation, 60–65 % of FLUTD cases), (2) urolithiasis (struvite or calcium oxalate, 15–20 %), and (3) urethral plugs (proteinaceous matrix ± crystals, 10–20 %). FIC is a diagnosis of exclusion made in a young to middle-aged, indoor, overweight, dry-food-fed, multi-cat-household cat with haematuria, pollakiuria, and periuria — and a negative urinalysis for bacteria, a negative urine culture, and no uroliths on imaging.
The Feline Respiratory System and Thoracic Cavity
The feline respiratory tract is similar to the dog's in basic structure, but several features deserve specific attention because of breed-related pathology and the cat's tendency to hide respiratory disease until it is advanced.
| Structure | Feline Feature | Clinical Significance |
|---|---|---|
| Nasal cavity / sinuses | The frontal sinus is small; the sphenoid sinus is absent in the cat. The nasal turbinates are delicate and easily damaged | Feline chronic rhinosinusitis (FCRS) is a common cause of chronic nasal discharge and sneezing. CT is the imaging modality of choice. Nasal neoplasia (lymphoma, adenocarcinoma) is also common and must be differentiated from FCRS by biopsy |
| Larynx | The feline larynx is more cranial than the dog's, which can make endotracheal intubation more challenging. The arytenoid cartilages are small and easily traumatised | Laryngeal paralysis is less common in cats than dogs. When it occurs, it is usually part of a more generalised neuropathy or myopathy. Laryngospasm during intubation is more common in cats than dogs — use topical lidocaine spray on the arytenoids before intubation (0.1–0.2 mL of 2 % lidocaine) |
| Trachea | The feline trachea is proportionally narrower than the dog's and is more susceptible to iatrogenic trauma during intubation | Tracheal rupture from overinflation of the endotracheal tube cuff is a recognised complication in cats. Use a low-pressure, high-volume cuff, and inflate to the minimum occlusive volume. If the cuff requires >2 mL of air in a 5 kg cat, the tube is too large — downsize |
| Lungs | The feline lung lobes are the same as the dog (six lobes), but the accessory lobe is proportionally larger | Feline asthma (eosinophilic bronchitis) is a common respiratory disease — it causes a bronchial pattern on radiographs ('donuts and tramlines') and can progress to bronchiectasis. It is managed with corticosteroids (inhaled fluticasone is ideal) and bronchodilators (inhaled albuterol for acute episodes). Feline asthma is a differential for any cat with a chronic cough — do NOT assume hairballs |
| Diaphragm | Same anatomy as the dog; the caval foramen, oesophageal hiatus, and aortic hiatus are at the same vertebral levels | Congenital peritoneopericardial diaphragmatic hernia (PPDH) is more common in cats than dogs — it is a defect in the ventral diaphragm and pericardium that allows abdominal contents to herniate into the pericardial sac. It is often an incidental finding (the cat is asymptomatic), but large hernias can cause cardiac tamponade and respiratory distress |
The Feline Endocrine System: Thyroid, Adrenal, and Pancreatic
The feline endocrine system has several unique features that affect disease presentation and treatment:
- Thyroid gland: The feline thyroid has no isthmus — the two lobes are completely separate and lie dorsolateral to the trachea. Hyperthyroidism (functional thyroid adenoma or adenomatous hyperplasia — usually benign) is the most common endocrine disease of geriatric cats (>8 years). The enlarged lobe(s) descend ventrally along the trachea and may be palpable at the thoracic inlet. Treatment options: methimazole (medical), radioactive iodine (I-131 — curative), surgical thyroidectomy (curative but risk of hypoparathyroidism if the parathyroid glands are removed or devascularised).
- Parathyroid glands: The feline parathyroid glands (two pairs: external and internal) are located at the cranial pole of each thyroid lobe. They are small (1–2 mm) and easily damaged during thyroidectomy. Hypoparathyroidism → hypocalcaemia → tetany, seizures, death. Post-thyroidectomy, monitor ionised calcium every 12 hours for the first 72 hours.
- Adrenal glands: The feline adrenal glands are proportionally larger than the dog's. Hyperadrenocorticism (Cushing's disease) is rare in cats and is usually caused by a functional pituitary adenoma. More commonly, the adrenal glands are affected by hyperaldosteronism (Conn's syndrome) — a functional adrenocortical tumour causing hypertension, hypokalaemia, and polymyopathy (cervical ventriflexion is pathognomonic).
- Pancreatic islets: The feline endocrine pancreas is similar to the dog's but has a higher density of islets in the left lobe. Diabetes mellitus in cats is most commonly type 2 (insulin resistance + relative insulin deficiency), associated with obesity and a high-carbohydrate dry-food diet. Diabetic remission (restoration of euglycaemia without exogenous insulin) is possible in up to 50 % of newly diagnosed cats with aggressive dietary management (low-carbohydrate, high-protein wet food) and tight glycaemic control.
Clinical Decision Table: The Vomiting Cat vs the Vomiting Dog
Vomiting is a common presenting sign in both species, but the differential list — and the diagnostic approach — differs because of feline-specific anatomy and pathology.
| Cause | Cat-Specific Features | Dog-Specific Features | Diagnostic Test | Key Treatment Difference |
|---|---|---|---|---|
| Linear foreign body | COMMON — thread, string, tinsel anchored under the tongue. Always check under the tongue of a vomiting cat. The foreign body 'saws' through the mesenteric border of the intestine, causing multiple perforations | Less common; linear foreign bodies do occur but are more often associated with cloth or rope | Oral examination (anchor under tongue); abdominal palpation ('pleated' intestines); ultrasound (pleating, hyperechoic linear structure) | Surgical removal via multiple enterotomies (the foreign body cannot be pulled from one site — it must be removed in segments). NEVER pull a linear foreign body from the oral cavity — you will saw through the intestinal wall |
| Hairballs (trichobezoars) | COMMON — cats ingest hair during grooming. Hairballs are usually vomited without complication, but large trichobezoars can cause obstruction | Rare — dogs do not groom themselves in the same way and rarely develop hairball obstruction | Abdominal palpation (firm, mobile mid-abdominal mass); ultrasound (hyperechoic mass with acoustic shadowing) | Most hairballs pass or are vomited without intervention. An obstructive trichobezoar requires surgical removal (gastrotomy or enterotomy). Prevention: regular grooming, hairball-formula diets, laxatone |
| Pancreatitis | Often idiopathic; associated with triaditis (pancreatitis + cholangiohepatitis + IBD). Clinical signs are vague (anorexia, lethargy, hiding) — vomiting is less consistent than in dogs | Often dietary indiscretion; clinical signs are more overt (vomiting, 'praying' position, abdominal pain) | fPLI (feline pancreatic lipase immunoreactivity — SPEC cPL for cats) is the test of choice; abdominal ultrasound (enlarged, hypoechoic pancreas with surrounding hyperechoic mesentery) | Feline pancreatitis: aggressive fluid therapy (crystalloids), antiemetics (maropitant), pain management (buprenorphine), early enteral nutrition (naso-oesophageal tube). Corticosteroids are controversial but may be indicated if an inflammatory component is suspected (triaditis) |
| Hepatic lipidosis | UNIQUE TO CATS — after 48–72 hours of anorexia, lipid accumulates in hepatocytes causing cholestasis and hepatic failure. The liver becomes enlarged, pale, and friable | Rare; dogs rarely develop hepatic lipidosis in the same way. Hepatic lipidosis in dogs is usually secondary to another disease (diabetes, pancreatitis) | Liver enzymes (ALP >> ALT — ALP is markedly elevated in feline lipidosis); bilirubin (elevated); abdominal ultrasound (diffusely hyperechoic, enlarged liver); cytology (lipid vacuoles in hepatocytes) | EARLY, AGGRESSIVE ENTERAL NUTRITION is the only effective treatment — place an oesophagostomy or naso-oesophageal tube and feed a high-protein, high-calorie diet. Appetite stimulants (mirtazapine) alone are insufficient once lipidosis has developed. Mortality is >50 % without nutritional support |
| Intestinal lymphoma | The most common GI neoplasia in older cats (>10 years). Can cause vomiting, diarrhoea, weight loss, and a palpable mid-abdominal mass. Often infiltrative rather than a discrete mass | Less common; GI lymphoma does occur but intestinal adenocarcinoma is relatively more common in dogs | Abdominal ultrasound (thickened intestinal wall with loss of layering); full-thickness intestinal biopsy (not endoscopic — endoscopic biopsies sample only the mucosa and miss the submucosal and muscular infiltrates of lymphoma) | Chemotherapy (CHOP or COP protocol) — feline intestinal lymphoma is often responsive to chemotherapy, with remission rates of 50–70 % for small-cell lymphoma. Surgical resection is reserved for discrete, obstructive masses |
- Propofol can be used safely for single-dose induction in cats but should not be used for prolonged maintenance (TIVA) — cats have impaired glucuronidation of propofol's phenolic metabolites, leading to oxidative injury of erythrocytes (Heinz body anaemia) with repeated or prolonged dosing.
- The feline pancreas has only one duct (the pancreatic duct, which joins the common bile duct at the major duodenal papilla). The accessory pancreatic duct is absent in the cat — unlike the dog, where it is the larger of the two. This means that biliary obstruction in a cat also obstructs the pancreas.
- The feline thyroid gland has no isthmus — the two lobes are completely separate, lying dorsolateral to the trachea, and they are NOT palpable in the normal cat. If you can palpate a thyroid lobe, it is enlarged — hyperthyroidism is the most common cause.
- Cats have a unique pelvic limb saphenous nerve distribution: the saphenous nerve (femoral n. branch) supplies the medial aspect of the crus and pes. A femoral nerve block provides anaesthesia to the medial crus — useful for medial stifle surgery. A sciatic nerve block provides anaesthesia to the lateral and caudal crus.
- The feline tympanic bulla is divided by a bony septum into a small dorsolateral compartment and a large ventromedial compartment. The septum must be perforated during a ventral bulla osteotomy to access both compartments — incomplete removal is the most common cause of recurrent otitis media after bulla surgery.
Frequently asked questions
Cats lack functional UGT1A6 — the UDP-glucuronosyltransferase enzyme responsible for conjugating and detoxifying the toxic metabolite of paracetamol, NAPQI (N-acetyl-p-benzoquinone imine). Without glucuronidation, NAPQI accumulates, causing: (1) oxidative injury to erythrocytes → Heinz body formation → haemolytic anaemia, (2) oxidation of haemoglobin → methaemoglobinaemia (chocolate-brown mucous membranes, respiratory distress), and (3) centrilobular hepatic necrosis. A single 325 mg tablet (10–50 mg/kg) can be fatal. Treatment (within 2–4 hours of ingestion): N-acetylcysteine (140 mg/kg IV/PO loading, then 70 mg/kg q6h for 7 treatments), S-adenosylmethionine (SAMe, 180 mg PO q24h), ascorbic acid (30 mg/kg IV q6h — reduces methaemoglobin to haemoglobin), and supportive care. Without treatment, mortality is >90 %.
Feline intubation requires more care than canine intubation because the feline larynx is more cranial, more sensitive (laryngospasm is common), and the trachea is narrower and more easily traumatised. Technique: (1) pre-oxygenate the cat for 3–5 minutes. (2) Apply 0.1–0.2 mL of 2 % lidocaine to the arytenoid cartilages with a 1 mL syringe and 25G needle — wait 30–60 seconds for the local anaesthetic to take effect. This reduces laryngospasm. (3) Use a laryngoscope with a small blade (Miller 0 or 1) to visualise the arytenoids. (4) Pass a styleted endotracheal tube (3.0–4.5 mm ID for an average 5 kg cat) through the rima glottidis. (5) Inflate the cuff to the MINIMUM occlusive volume — if it takes >2 mL of air, the tube is too large. (6) Confirm placement by capnography, bilateral thoracic auscultation, and palpation of the cuff at the thoracic inlet. (7) NEVER force the tube — if the arytenoids are in spasm, wait 30 seconds, re-apply lidocaine, and try again. Forcing the tube causes laryngeal trauma, oedema, and post-extubation stridor.
Feline triaditis is the concurrent occurrence of three inflammatory diseases: (1) pancreatitis, (2) cholangiohepatitis (inflammation of the bile ducts and hepatic parenchyma), and (3) inflammatory bowel disease (IBD). The anatomical basis is the common drainage of the pancreatic duct and common bile duct into the major duodenal papilla. Inflammation or infection ascending from the duodenum can simultaneously involve the pancreas, bile ducts, and intestine. Additionally, the portal circulation carries inflammatory mediators from the intestine to the liver, and from the pancreas to the liver. Triaditis is a clinical diagnosis suspected when a cat has vomiting, anorexia, icterus, and weight loss, with elevated liver enzymes, elevated fPLI, and ultrasonographic changes in all three organs. Definitive diagnosis requires biopsy of all three organs — which is rarely performed in clinical practice. Treatment is supportive: fluid therapy, antiemetics, pain management, ursodeoxycholic acid (for cholangitis), and immunosuppressive doses of prednisolone (2 mg/kg q12h initially) if a significant inflammatory component is suspected.
The male feline urethra is long, narrow, and has two acute bends (at the ischial arch and at the glans penis). The penile urethra — the narrowest point — is <0.5 mm in diameter at the tip in a 5 kg cat. Urethral plugs (proteinaceous matrix ± struvite crystals) — the most common cause of obstruction — become lodged at this narrow point. The female feline urethra is short, straight, and wide — the same plug that obstructs a male cat would pass easily through a female urethra. Additionally, male cats have a higher incidence of FLUTD (possibly related to stress, territorial behaviour, and concentrated urine from lower water intake). Obstructed male cats present with stranguria, vocalisation, and a large, firm, painful bladder on palpation. Untreated, post-renal azotaemia, hyperkalaemia, and metabolic acidosis develop within 24–48 hours. Hyperkalaemia causes bradycardia and cardiac arrest — this is the cause of death in untreated feline urethral obstruction.
The dog has TWO pancreatic ducts: the accessory pancreatic duct (which drains into the minor duodenal papilla — this is the larger of the two ducts in the dog) and the pancreatic duct (which joins the common bile duct and drains into the major duodenal papilla). The cat has only ONE duct: the pancreatic duct, which joins the common bile duct and drains into the major duodenal papilla. The accessory pancreatic duct is absent in the cat. This means that: (1) biliary obstruction in a cat also obstructs the pancreas → pancreatitis can develop secondary to extrahepatic biliary obstruction, and (2) surgical manipulation of the duodenum or common bile duct in a cat carries a higher risk of iatrogenic pancreatitis than in a dog because the common drainage pathway means that any oedema or inflammation at the papilla can obstruct pancreatic outflow.
Heinz bodies are foci of oxidatively denatured haemoglobin that precipitate on the inner surface of the erythrocyte membrane. They are visible on a blood smear as small, pale, refractile projections from the erythrocyte surface (with Romanowsky stains) or as dark blue-black inclusions (with new methylene blue supravital stain). Cats are uniquely susceptible to Heinz body formation because: (1) feline haemoglobin has 8–10 reactive sulfhydryl groups (compared to 2–4 in dogs and humans) — more sites for oxidative damage, and (2) the feline spleen is less efficient at removing Heinz bodies (the splenic sinusoids are structured differently). Normal cats can have up to 1–5 % Heinz bodies in their erythrocytes without anaemia. Pathological Heinz body anaemia occurs with: paracetamol toxicity, propofol (repeated dosing), onion/garlic ingestion (thiosulphates cause oxidative injury), diabetes mellitus, hyperthyroidism, and lymphoma. Treatment: remove the inciting cause, administer N-acetylcysteine or SAMe (antioxidants), and provide supportive care. The anaemia resolves as the damaged erythrocytes are removed by the spleen and replaced by new erythrocytes from the bone marrow (3–5 days).
Self-check quiz
Test yourself. Answers are below each question — cover them first if you are studying.
- A) Ibuprofen
- B) Paracetamol (acetaminophen)
- C) Meloxicam
- D) Aspirin
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Answer: B) Paracetamol (acetaminophen)
Chocolate-brown mucous membranes (methaemoglobinaemia) + haemolytic anaemia (pale) in a cat after a human painkiller is classic for paracetamol toxicity. Cats cannot glucuronidate paracetamol. Ibuprofen causes GI ulceration and renal failure, not methaemoglobinaemia. Meloxicam at feline doses is relatively safe. Aspirin causes acidosis and gastric ulceration, not methaemoglobinaemia.
- A) The clavicular remnant
- B) The supracondylar foramen
- C) The acromion process
- D) The os penis
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Answer: A) The clavicular remnant
The feline clavicle is a tiny (2–3 mm) ovoid mineralised ossicle in the clavicular tendon, visible cranial to the shoulder joint on thoracic radiographs. It is NORMAL and should not be mistaken for a fracture fragment or foreign body. The supracondylar foramen is in the distal humerus. The acromion is part of the scapula. The os penis is only in male dogs — cats do not have an os penis.
- A) Start IV fluids and antibiotics
- B) Relieve the urethral obstruction by catheterisation
- C) Perform an emergency cystotomy
- D) Obtain a urine sample for culture
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Answer: B) Relieve the urethral obstruction by catheterisation
Feline urethral obstruction is a life-threatening emergency. Hyperkalaemia causes bradycardia and cardiac arrest — death can occur within 24–48 hours. The immediate priority is to relieve the obstruction (catheterisation). IV fluids are started concurrently, but catheterisation takes precedence. Cystotomy is reserved for cases where catheterisation fails or for cystotomy to remove uroliths. Urine culture can wait — the cat is obstructed, not infected, in the majority of cases (FIC is sterile inflammation).
- A) The liver, pancreas, and intestine share the same arterial supply
- B) The pancreatic duct and common bile duct merge before draining into the duodenum, and the portal circulation connects the three organs
- C) Cats have a shorter GI tract, making all three organs more susceptible to bacterial translocation
- D) The three organs are all derived from the same embryonic germ layer (endoderm)
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Answer: B) The pancreatic duct and common bile duct merge before draining into the duodenum, and the portal circulation connects the three organs
In cats, the pancreatic duct merges with the common bile duct into a single channel before draining into the major duodenal papilla. This means that inflammation or infection can ascend from the duodenum to involve all three organs. Additionally, the portal vein carries blood from the pancreas and intestine to the liver, providing a second anatomical connection. This shared drainage anatomy is unique to cats (dogs have a separate accessory pancreatic duct).
- A) Propofol
- B) Alfaxalone
- C) Thiopental
- D) Ketamine alone
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Answer: B) Alfaxalone
Propofol should not be used for TIVA in cats because its phenolic metabolites require glucuronidation for excretion — cats have impaired glucuronidation, and repeated or prolonged propofol dosing causes Heinz body anaemia. Alfaxalone is a neuroactive steroid with no phenolic metabolites, making it safe for TIVA in cats. Thiopental is a barbiturate with a long recovery. Ketamine alone causes rough recoveries and increases intraocular and intracranial pressure.
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