Normal imaging
Radiological assessment of the normal spleen is based on comparing it with surrounding organs, primarily the liver and muscles.
- Ultrasound (US): The organ is visualized above the left kidney. The parenchyma has a homogeneous structure; echogenicity varies from medium to low. The upper limit of normal for the craniocaudal size is 12 cm.
- Computed tomography (CT): In the unenhanced phase, the structure is homogeneous, and X-ray density is 5–10 Hounsfield units (HU) lower than that of the liver. With intravenous contrast enhancement in the arterial (early parenchymal) phase, a typical "striped" pattern (striped) appears. It is caused by varying blood flow rates through the cords of the red pulp. In the venous and late phases, contrast enhancement becomes completely uniform.
- Magnetic resonance imaging (MRI): On T1-weighted images, the signal from the spleen is lower than from the liver, but slightly higher than from muscle tissue. On T2-weighted images, the signal intensity is consistently higher than that of the liver.
Congenital developmental anomalies
The most common finding is accessory spleen (splenunculus). It is usually a spherical lesion ranging from several millimeters to centimeters in size, located near the splenic hilum. The main diagnostic criterion is that its tissue behaves absolutely identically to the main spleen in all phases on CT and MRI (including fat-suppressed T2, 3D T1 arterial, portal-venous, and delayed phases). When atypically located, splenunculus may mimic a tumor. After removal of the main spleen, accessory lobules tend to undergo compensatory enlargement.
Rare malformations include polysplenia (multiple small spleens, more common in women, associated with situs ambiguous) and asplenia (complete absence of the organ, more common in men, combined with situs inversus). These conditions are frequently accompanied by other rotational anomalies affecting the heart, liver, and inferior vena cava.
Traumatic injuries
Acute and delayed splenic ruptures are life-threatening due to massive hemorrhage. However, modern management implies maximally conservative care to preserve the organ and avoid severe post-splenectomy pneumococcal infections.
The method of choice is multiphasic CT with intravenous contrast enhancement (sensitivity and specificity exceed 95%).
- Hematomas: On unenhanced scans, they can be isodense or hyperdense relative to the parenchyma. They do not enhance with contrast. If a focal area of contrast enhancement is identified within a hematoma, this is a direct sign of active bleeding.
- Subcapsular hematoma: Appears as a well-defined crescentic fluid collection along the organ contour. This is a marker of trauma even without a visible defect in the parenchyma itself.
- Ruptures: Linear hypodense tissue defects that are almost always combined with hemoperitoneum. A rupture extending completely across two surfaces of the capsule is classified as a fracture (fracture).
Ultrasound is insufficiently sensitive to exclude acute trauma, but is used to monitor the resorption of previously known hematomas.
Infectious lesions
Infections more commonly affect immunocompromised patients. Predisposing factors for abscesses include previous trauma or splenic infarction.
- Bacterial abscesses: On CT, these are spherical or lobular hypodense zones. Unlike liver abscesses, they are not characterized by a contrast-enhancing capsular rim. Very rarely, gas may be detected inside.
- Fungal infections: Large lesions form the "target appearance" (target appearance). The central necrotic core is hypodense on CT (hypoechoic on ultrasound), surrounded by a hyperdense ring of viable mycelium, which is encircled by a hypodense zone of peripheral inflammation. On MRI, such lesions are hypointense on T1 and hyperintense on T2.
- Tuberculosis: In the miliary form, multiple small hypodense lesions are visible on CT, and hyperechoic inclusions («bright spleen» or «salt-and-pepper» sign) on ultrasound. In the focal form, tuberculomas (1–3 cm) are formed, which tend to calcify upon chronicity.
Briefly: answers to topical questions
What are the normal dimensions of the spleen determined by ultrasound?
During ultrasound, the normal craniocaudal size of the spleen is less than 12 cm. The normal spleen is located above the left kidney.
Which blood vessels pass through the splenic hilum and form its vascular pedicle?
Blood vessels and nerves passing through the splenic hilum (hilum lienale) form its vascular pedicle. The following structures pass through the longitudinal sulcus on the visceral surface of the organ:
- Splenic artery (splenic artery) — enters the organ hilum, providing arterial inflow.
- Splenic vein (v. lienalis) — exits the hilum, providing venous outflow. Its diameter is 1.5–2 times larger than the corresponding artery.
Nerves also enter the organ through the hilum. The hilum itself is located in the central part of the inner surface along the longitudinal axis of the spleen.
To avoid confusing an accessory spleen with a lymph node or tumor, use the "mirror rule": in all CT and MRI phases without exception, the accessory nodule accumulates and washes out contrast strictly synchronously with the main parenchyma.
Class and exam questions
Why does the spleen look "striped" in the arterial phase of CT, and is this pathological?
This is a completely normal transitional pattern. It occurs due to the varying passage rate of contrasted blood through the red pulp structures. In the subsequent venous phase, the parenchyma equalizes and becomes homogeneous.
Which diagnostic imaging method is preferred for suspected splenic trauma?
The gold standard is multiphasic contrast-enhanced computed tomography (CT). It allows the detection of ruptures, hematomas, and signs of ongoing active bleeding with an accuracy of over 95%.
How to differentiate a bacterial splenic abscess from a liver abscess on CT?
Unlike typical liver abscesses, splenic abscesses usually do not have a clearly visualized enhancing capsular rim after contrast administration.
What else to study on this topic
- Pathogenesis and CT findings of splenic infarction in splenic artery branch occlusion
- Differential diagnosis of an accessory spleen with atypical localization
- Association of polysplenia and asplenia with situs ambiguous and situs inversus syndromes
- Ultrasound "salt-and-pepper" pattern in granulomatous infections
- Role of ultrasound in the follow-up of posttraumatic subcapsular hematomas
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