Ultrasound appearance and normal dimensions
During an ultrasound examination (US), a healthy spleen demonstrates a homogeneous (uniform) structure. Its echogenicity ranges from medium to low values. The organ is visualized in the left hypochondrium, lying directly above the left kidney.
The main parameter to consider when evaluating dimensions is the maximum craniocaudal size. Normally, it is less than 12 cm. If this indicator exceeds the threshold value of 12 cm, splenomegaly (enlargement of the organ) is diagnosed. However, it is important to understand that an isolated size assessment does not always correlate with the presence of pathology. For example, in non-Hodgkin lymphoma, the organ may be of normal size in up to one-third of patients.
Topographic anatomy and structural features
The shape of the organ is closely related to the surrounding anatomical structures. The external contours have the following characteristics:
- Lateral surface: convex and completely smooth. It precisely replicates the shape of the adjacent abdominal wall and the left dome of the diaphragm.
- Medial surface: has a concave shape.
In diagnostic radiology practice, normal structural variants in the form of pronounced lateral and inferior clefts (clefts) due to lobular structure are frequently encountered. It is important to remember that on ultrasound and CT, these natural sulci can be mistaken for post-traumatic parenchymal lacerations.
Blood supply to the organ is provided by the splenic artery (a. splenica), which branches off the celiac trunk (truncus coeliacus). Venous outflow occurs via the splenic vein (v. splenica), which empties into the portal vein system (v. portae). Since the splenic artery is an end artery, occlusion of any of its branches almost always leads to an infarction of the corresponding parenchymal area.
Congenital developmental anomalies
The normal radiological appearance may be altered due to frequent congenital variants:
- Accessory spleen (splenunculus): an extremely common finding representing tissue separated from the main organ mass, ranging from a few millimeters to centimeters in size. It is most often localized in the region of the organ hilum. Tissue contrast and enhancement patterns are identical to the normal spleen. Following removal of the main organ (splenectomy), accessory lobes may enlarge while maintaining a spherical shape. When located atypically, they are frequently mistaken for tumors.
- Polysplenia: the presence of multiple small lobules instead of a single large organ. This condition is more frequently detected in women and is closely associated with situs ambiguous syndrome (heterotaxy).
- Asplenia: congenital absence of the spleen. This anomaly is more common in males and is associated with the inversion of internal organs (situs inversus).
Both polysplenia and asplenia are rare anomalies that are frequently combined with other symmetry and rotation disorders affecting the heart, liver, inferior vena cava, and mesentery.
Comparison of normal appearance on CT and MRI
To clarify the diagnosis and when pathology is suspected, ultrasound is supplemented with tomographic methods:
- Computed tomography (CT): On unenhanced scans, the parenchyma is homogeneous, and its X-ray attenuation is 5–10 HU lower than the density of a healthy liver. With intravenous contrast enhancement in the arterial (or early parenchymal) phase, a characteristic striped appearance is observed. This is a completely normal phenomenon caused by varying blood flow velocities in the red pulp cords. In the subsequent venous and delayed phases, the enhancement equalizes.
- Magnetic resonance imaging (MRI): On T1-weighted images (T1WI), the signal from the spleen is lower than that from the liver, but slightly higher than the signal from skeletal muscle. On T2-weighted images, the signal intensity from splenic tissue is consistently higher than that from the hepatic parenchyma.
The threshold size is easy to remember using a dozen—normality ends right at 12 cm. Blood supply: "The celiac trunk provides nutrition (a. splenica), and the portal vein collects the tribute (v. splenica)."
Class and exam questions
What splenic size on ultrasound is considered the upper limit of normal?
The maximum craniocaudal size should not exceed 12 cm. Exceeding this threshold is the criterion for splenomegaly.
Why does the spleen appear striped on contrast-enhanced CT?
In the arterial phase, a striped pattern occurs due to differing blood flow velocities in the red pulp cords. In the venous phase, this effect disappears.
Can lymphoma be ruled out if splenic dimensions are normal?
No, isolated size assessment is unreliable. Up to one-third of patients with histologically confirmed splenic lymphoma do not have splenomegaly.
What is a splenunculus?
This is an accessory spleen—a frequently occurring congenital variant. In terms of echogenicity and contrast enhancement, it is completely identical to the main organ.
What else to study on this topic
- Radiological diagnostics and management tactics in splenic trauma (evaluation of hematomas and lacerations on CT)
- Infectious lesions: abscesses, fungal foci ("target" sign), and tuberculosis
- Differential diagnosis of cystic lesions (true cysts, parasitic cysts, and pseudocysts)
- Malignant neoplasms of the spleen: patterns of angiosarcoma and lymphoma
- Application of contrast-enhanced ultrasound (CEUS) in focal pathology
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