Intraperitoneal lymphatic organ located posterior to stomach and intimately associated with retroperitoneum (pancreatic tail and left kidney)

Surrounded by peritoneum (except at hilum) and suspended by several ligaments

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  Gastrosplenic ligament

  
  
  
  
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    Left anterior margin of lesser sac

    
    
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    Connects spleen to greater curvature of stomach

    
    
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    Carries short gastrics and left gastroepiploic arteries and venous branches to spleen

  
  
  
  
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  Splenorenal ligament

  
  
  
  
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    Left posterior margin of lesser sac

    
    
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    Connects spleen to left kidney and pancreatic tail

    
    
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    Carries splenic artery and vein to splenic hilum

  
  
  
  
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  Splenocolic ligament: Between spleen and splenic flexure of colon

  
  
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  Splenophrenic ligament: Between spleen and inferior surface of diaphragm

Normal size is variable ; no universal consensus

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  Generally, normal adult spleen considered 12-cm length x 7-cm width x 4cm thickness

  
  
  
  
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    Length = longest diameter in longitudinal plane; width = longest transverse (anterior-posterior) diameter; thickness = maximal thickness in transverse plane at hilum

  
  
  
  
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  Splenic index (product of length, thickness, and width): Normally 120-480 cm³

  
  
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  Size correlates with height and can exceed these limits in tall, healthy people

Functions

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  Manufactures lymphocytes, filters blood (removes damaged red blood cells and platelets)

  
  
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  Acts as blood reservoir: Can expand or contract in response to changes in blood volume

Histology

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  Soft organ with fibroelastic capsule and comprised of pulp

  
  
  
  
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    White pulp: Lymphoid nodules/tissue primarily surrounding vasculature

    
    
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    Red pulp: Sinusoidal spaces containing blood

  
  
  
  
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  Trabeculae: Extensions of capsule into parenchyma; carry arterial and venous branches

  
  
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  Splenic cords (plates of cells) lie between sinusoids; red pulp veins drain sinusoids

Vasculature

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  Splenic artery arises from celiac axis in > 90%; 8% directly from aorta

  
  
  
  
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    Often very tortuous

  
  
  
  
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  Splenic vein runs in groove along dorsal surface of pancreatic body and tail

  
  
  
  
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    Receives inferior mesenteric vein (IMV)

    
    
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    Combined splenic vein and IMV join superior mesenteric vein to form portal vein

  
  

Homogeneous echogenicity

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  Echogenicity: Pancreas > spleen > liver > kidney

  
  
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  Radiating pattern of segmental arteries and veins

Splenic artery

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  Low-resistance waveform; tortuosity of vessel results in turbulence and spectral broadening

  
  
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  Normal diameter: 4-8 mm; peak systolic velocity (PSV): 25-45 cm/s

  
  
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  Retrograde flow can be seen in setting off celiac trunk occlusion

Splenic vein

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  Normal diameter: 5-10 mm; PSV: 9-18 cm/s

  
  
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  Splenic vein at midline is useful landmark for locating pancreas

  
  
  
  
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    Pancreas lies anterior to splenic vein

  
  
  
  
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  Diameter increases between 50-100% from quiet respiration to deep inspiration; increase of < 20% suggests portal hypertension

  
  
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  Spectral Doppler waveform typically shows band-like flow profile with minimal respiratory fluctuations

Patient positioned supine or right decubitus position (left side up) with left arm raised

Place transducer parallel to ribs in 10th or 11th intercostal space at left midaxillary line, searching for best window

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  Due to rib angle, this results in oblique view, which by convention is called longitudinal or transverse (depending on transducer orientation)

  
  
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  Transverse US view of spleen does not correlate directly to axial CT view

End expiration may be helpful; lung base may obscure spleen in full inspiration

Spleen poorly accessed from posterior (obscured by left lung base), anterior, or subcostal approach (obscured by stomach and colon)

Assess splenic vein at hilum and midline for patency and flow direction

Can use spleen as acoustic window to visualize tail of pancreas

Left lobe of liver may extend superior to the spleen and should not be mistaken for splenic lesion

Spleen has highly variable size and shape

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  Easily indented and displaced by masses and even loculated fluid collections

  
  
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  Imaging reliably detects splenomegaly and may suggest its cause (whether diffuse or due to space occupying lesion; extrasplenic clues, e.g., with cirrhosis = portal hypertension; with lymphadenopathy = lymphoma, mononucleosis, etc.)

Spleen is commonly injured in blunt trauma, especially with fracture of left lower ribs

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  Parenchymal laceration and capsular tear often result in substantial intraperitoneal bleeding

Accessory spleen (splenunculus, splenule)

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  Found in 10-30% of population and may be multiple

  
  
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  Usually small, near splenic hilum

  
  
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  Can enlarge and simulate mass, especially after splenectomy

  
  
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  Ectopic intrapancreatic splenule can mimic pancreatic tail mass; should not be > 3 cm from tail tip

Wandering spleen : Spleen may be on long mesentery

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  Found in any abdominopelvic location; risk of torsion

Asplenia and polysplenia (heterotaxy syndromes)

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  Rare congenital conditions of altered left/right orientation of organs

  
  
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  Associated with cardiovascular anomalies, intestinal malrotation, etc.

Splenosis : Peritoneal implantation of splenic tissue after traumatic splenic injury, can mimic polysplenia