The spleenModalities
Plain radiography
The size of the spleen may be roughly estimated on the plain film, especially if the organ is enlarged. Calcified lesions such as granulomas or cyst walls, are well seen.
Ultrasonography
US gives good information on the shape and size of the spleen and on any pathological changes that may be present. Splenomegaly can be identified and measured. Cysts are seen as well-demarcated echo-free structures. Tumours and metastases have an echogenicity differing from that of normal splenic parenchyma, being either hypo- or hyper-echogenic. Lesions as small as 1 cm may be identified, with the exception of diffuse infiltrates such as lymphoma, which may be difficult to discern on US. Traumatic changes, such as rupture of the spleen and haemorrhage, are clearly seen on US, as are infarctions and abscesses.
Computed tomography
The best images of the spleen are obtained by CT, which also gives information on any calcification present, e.g. in granulomas or cyst walls and allows precise measurement of splenic size. Pathological changes are seen, as on US, but often with greater clarity, especially after i.v. contrast infusion.
Magnetic resonance imaging
On MRI diffuse infiltrates such as occur, for instance, in lymphoma, may be seen more clearly than on US and CT, but essentially MRI and CT are of equal value. The free choice of imaging plane may be one advantage offered by MRI.
Localized changes, such as cysts, metastatic deposits, tumours and infarcts can be shown by radionuclide imaging, though the specificity and spatial resolution of the technique are inferiorto US and CT. Intrasplenic abscess is difficult to image with radiolabelled leucocytes because the spleen is a normal site of granulocyte pooling and is therefore very prominent in a white cell scan. An abscess may be identified by sequential imaging, during which an abscess is seen to increase in activity in comparison with normal splenic tissue which shows a slight fall, or by subtraction imaging using Tc-99m labelled sulphur colloid.
Images of splenic function may be obtained with autologous radio labelled blood cells, including heat denatured erythrocytes, platelets, and leucocytes. Such imaging may be useful for the localization of functioning splenunculi and the assessment of the role of the spleen in thrombocytopenia, particularly ITP.
Angiography is not often used for diagnostic purposes (except in acute bleeding) but may be used as a step in embolizing the spleen or splenic artery in the treatment of hypersplenism, trauma or aneurysm. Direct splenoportography, i.e. direct puncture of the spleen and the injection of contrast medium into the splenic parenchyma through a plastic cannula, may be performed to map the venous drainage of the spleen in portal hypertension. With modem digital subtraction equipment, however, the requisite information can now almost always be obtained by indirect splenoportography using the venous phase of a splenic arteriogram and the direct method is virtually obsolete in advanced centres.
David J. Allison and Carl-Gustaf Standertskjold-Nordenstam