Overview
The equine spleen (lien) is large and falciform: wide at the dorsal end and narrow at the ventral end. Its capsule and trabeculae contain abundant smooth muscle, so it can contract strongly. It filters blood, removes aged red cells, takes part in the immune response and stores a large reserve of red cells that is released during exercise or excitement.
Topography
- Position: in the left cranial abdomen, with its parietal surface against the diaphragm and the left costal wall.
- Dorsal end (base): under the last left ribs, next to the left kidney and the blind sac of the stomach.
- Ventral end (apex): narrow, it runs cranially and towards the median plane along the ventral abdominal wall; its size varies greatly with the degree of contraction.
- Ligaments: the gastrosplenic ligament joins it to the greater curvature of the stomach and the nephrosplenic ligament to the left kidney. The caudal border of the spleen can be palpated per rectum on the left side.
Clinical relevance
- Nephrosplenic entrapment: the left large colon hangs over the nephrosplenic ligament, between the spleen and the kidney; on ultrasound, the gas-filled colon hides the left kidney.
- Splenic contraction and PCV: adrenaline releases stored red cells and raises the packed cell volume; in an excited horse or after exercise the value does not reflect the resting state.
- Splenomegaly: some sedatives and anaesthetics (acepromazine, barbiturates) relax and enlarge the spleen; it is also enlarged in equine infectious anaemia, lymphoma and other diseases.
- Rupture and haematoma: from trauma (kicks) or tumour infiltration; they cause abdominal haemorrhage.
- Examination: ultrasound on the left side, through the last intercostal spaces and the flank, shows it clearly next to the left kidney.