Splenic hamartomas are very rare lesions commonly found incidentally on imaging. They are most often solitary but may be present as multiple nodules in patients with tuberous sclerosis or Wiskott-Aldrich syndrome.
The recently-described sclerosing angiomatoid nodular transformation (SANT) of the spleen, a non-neoplastic vascular entity named in 2004 5 may be a fibrosing variant of splenic hamartoma 6.
Splenic hamartomas are very rare, with only 3 described in a series of 200,000 splenectomies.
Hamartomas are normally an incidental finding at imaging, surgery or autopsy. They can occur in any age group. Symptoms occur from mass effect if they grow large.
Hamartomas are solitary or multiple, round, well-circumscribed, unencapsulated bulging nodules compressing the adjacent normal splenic parenchyma and compounded by a mixture of normal splenic structures such as white and red pulp. Focal fibrosis and cystic areas can be seen.
The pathological differential diagnosis includes haemangioma, Littoral cell angioma, lymphangioma, haemangioendothelioma, sclerosing angiomatoid nodular transformation (see terminology), angiosarcoma. A definite diagnosis can be difficult due to the overlap of features, however, positivity of CD8 is a key feature that differentiates hamartoma from other vascular lesions of the spleen.
As hamartomas represent a focal disorganised overgrowth of splenic parenchyma, they tend to have similar echogenicity, attenuation, and signal intensity to the background normal parenchyma 7.
Most splenic hamartomas are hypoechoic solid masses, but can be heterogeneous due to haemorrhage or cystic changes 7. They are hypervascular on colour Doppler ultrasound and post contrast administration.
On computed tomography, hamartomas appear as isodense or hypodense solid masses and demonstrate heterogeneous contrast enhancement relative to the adjacent normal parenchyma.
MRI is the preferred imaging technique for the differentiation of hamartomas from haemangiomas, showing:
- T1: most lesions are isointense
- T2: most lesions are heterogeneously hyperintense
T1 C+ (Gd):
- it is typical to show vivid enhancement on immediate post contrast-enhanced images (key features in the differentiation between hamartomas and haemangiomas)
- on delayed postcontrast images, hamartoma enhances in a relatively uniform and intense fashion +/- with central hypovascular areas
Possible differential considerations include
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- normal appearance of the spleen
- pseudolesion of the spleen: inhomogeneous splenic enhancement
splenic lesions and anomalies
- congenital anomalies
- mass lesions
- infiltrative processes
- incidental splenic lesion (approach)