Splenic hamartoma (splenoma) is a rare benign neoplasm of the spleen consisting of a disorganized but benign proliferation of red pulp elements (sinusoids, fibroblasts, vascular structures). Incidence is 0.024-0.13% in autopsy series. Usually discovered incidentally, asymptomatic, and mostly a solitary lesion. Rarely may be multiple and associated with tuberous sclerosis complex (TSC) — especially Wunderlich syndrome. Histologically composed of disorganized accumulation of mature red pulp structures; white pulp elements (lymphoid follicles) are absent or scarce. CD8 positivity and CD34 negativity are diagnostic. On imaging, it appears as a well-defined, solid, homogeneous or mildly heterogeneous mass showing enhancement pattern similar to splenic parenchyma. Treatment is generally not needed but splenectomy may be considered for large symptomatic lesions.
Age Range
30-70
Peak Age
50
Gender
Equal
Prevalence
Rare
Splenic hamartoma is a congenital or developmental disorganized proliferation of red pulp elements — not a true neoplasm but displaying a disorganized (hamartomatous) growth pattern. Histopathologically composed of anomalous sinusoidal vascular channels, fibroblasts, and reticular fibers; white pulp follicles (lymphoid tissue) are markedly absent. Sinusoids are lined by CD8+ endothelium (same as normal splenic sinusoids) but CD34-negative — this immunohistochemical profile differentiates from hemangioma (CD34+) and littoral cell angioma (CD68+). The red pulp-like vascular structure explains the enhancement pattern similar to splenic parenchyma: heterogeneous enhancement simultaneous with spleen in arterial phase, isodense to mildly hyperdense in portal venous phase → 'splenic tissue sign'. It shows isointense or mildly hyperintense signal to splenic parenchyma on T2-weighted MRI because tissue composition resembles normal splenic parenchyma. No marked diffusion restriction on DWI because the sinusoidal structure allows water diffusion (different from lymphoma's dense cell packing). TSC-associated hamartomas are linked to mTOR pathway activation through TSC1/TSC2 gene mutations.
A well-defined solid mass enhancing isodense to splenic parenchyma is called the 'splenic tissue sign'. This finding reflects hamartoma's red pulp-like vascular structure and differentiates from other solid splenic tumors (lymphoma — hypodense, metastasis — heterogeneous). Tc-99m sulfur colloid uptake confirms this diagnosis.
In the portal venous phase, a well-defined, homogeneous solid mass isodense or slightly hyperdense to splenic parenchyma is seen. This 'splenic tissue sign' reflects the red pulp-derived vascularity of hamartoma. Enhancement pattern parallels normal splenic parenchyma — enhances together in arterial phase, homogenizes together in portal venous phase. Mass margins are smooth and sharp. Mild heterogeneity and focal calcifications may be seen in large lesions (>5 cm).
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A well-defined, homogeneous solid mass isodense to splenic parenchyma in the portal venous phase is seen in the spleen, consistent with 'splenic tissue sign' of splenic hamartoma.
On T2-weighted MRI, hamartoma shows isointense or mildly hyperintense signal to splenic parenchyma. Signal is homogeneous. No marked 'light bulb sign' hyperintensity — differentiating from hemangioma. Mild hyperintensity results from slightly higher water content in sinusoidal channels compared to normal splenic parenchyma. Focal T2 hypointense areas in large lesions may reflect fibrotic bands or hemosiderin deposition.
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The splenic mass shows isointense to mildly hyperintense homogeneous signal to splenic parenchyma on T2-weighted MRI; without the marked hyperintensity of hemangioma.
On B-mode US, a well-defined, homogeneous solid mass isoechoic or mildly hyperechoic to splenic parenchyma is seen. Isoechoic lesions may be detected by focal lobulation or deformity of splenic contour. Doppler US shows vascularity similar to splenic parenchyma within the mass. Calcification foci may appear as echogenic foci.
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A well-defined solid mass isoechoic to splenic parenchyma is seen in the spleen on US, creating focal lobulation of the splenic contour.
In the arterial phase, hamartoma shows heterogeneous enhancement together with splenic parenchyma — the normal zebra pattern of the spleen may also be seen within the hamartoma. This 'simultaneous enhancement' reflects similar vascularity kinetics to splenic parenchyma and supports hamartoma diagnosis. In the portal venous phase, the lesion homogenizes and becomes isodense to splenic parenchyma.
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The splenic mass shows heterogeneous enhancement simultaneous with splenic parenchyma in the arterial phase, becoming isodense in portal venous phase; consistent with hamartoma.
On T1-weighted MRI, hamartoma shows isointense or mildly hypointense signal to splenic parenchyma. On post-contrast T1 series, homogeneous enhancement simultaneous with splenic parenchyma is seen — the hamartoma may 'disappear' into the splenic parenchyma as both take up similar amounts of gadolinium.
Report Sentence
The splenic mass shows isointense signal to splenic parenchyma on T1-weighted MRI and becomes masked by enhancing simultaneously with the splenic parenchyma on post-contrast series.
On Tc-99m sulfur colloid scintigraphy, hamartoma shows normal or mildly increased uptake because red pulp structures maintain reticuloendothelial system (RES) function. This feature is valuable in differentiating hamartoma from hemangioma (no uptake) and lymphoma (no or decreased uptake). It also shows uptake on Tc-99m heat-damaged RBC study.
Report Sentence
Normal to increased uptake is seen in the splenic mass on Tc-99m sulfur colloid scintigraphy; this finding is consistent with RES-preserving splenic hamartoma.
Criteria
Single lesion. Incidentally discovered. No syndrome association.
Distinct Features
Most common form. Usually <5 cm. Asymptomatic. No treatment needed.
Criteria
TSC1/TSC2 mutation. Multiple lesions may occur. Hamartomas in other organs (renal AML, brain tubers).
Distinct Features
mTOR pathway activation. Everolimus therapy may be considered. Genetic counseling and multi-organ screening required.
Criteria
Size >10 cm. May be symptomatic (pain, early satiety). Thrombocytopenia may accompany.
Distinct Features
Heterogeneous structure — fibrosis, calcification, cystic areas may be present. Splenectomy may be needed.
Distinguishing Feature
Hemangioma shows marked T2 hyperintensity ('light bulb sign') with peripheral nodular enhancement; hamartoma shows isointense to mildly hyperintense T2 with simultaneous parenchymal enhancement. Hemangioma shows no Tc-99m sulfur colloid uptake.
Distinguishing Feature
Both show Tc-99m sulfur colloid uptake but littoral cell angioma usually presents with multiple lesions and splenomegaly; hamartoma is usually solitary. LCA is CD68+/CD34-, hamartoma is CD8+/CD34-.
Distinguishing Feature
Lymphoma shows hypodense, minimally enhancing lesions with diffusion restriction on DWI; hamartoma shows isodense enhancement with splenic parenchyma without diffusion restriction.
Distinguishing Feature
Extramedullary hematopoiesis presents with multiple lesions and massive splenomegaly in the setting of myelofibrosis/hemolytic anemia; hamartoma is usually solitary without hematologic disease association.
Urgency
routineManagement
surveillanceBiopsy
Not NeededFollow-up
12-monthSplenic hamartoma is a benign lesion with no risk of malignant transformation. No treatment is needed for small, asymptomatic lesions — annual imaging follow-up is sufficient. Splenectomy or partial splenectomy may be considered for large or symptomatic lesions. Biopsy is generally not needed — imaging and Tc-99m sulfur colloid study are diagnostic. Tuberous sclerosis screening should be performed in the presence of multiple hamartomas. Partial splenectomy is preferred over total splenectomy to preserve splenic function.
Splenic hamartoma is usually incidentally discovered and has no malignant potential. Definitive diagnosis may be difficult on imaging, and splenectomy can be both diagnostic and therapeutic.