Splenic metastasis is a rare condition because the splenic microenvironment is resistant to metastatic colonization; this resistance is related to macrophage activity in splenic sinusoids, the spleen's immune surveillance function, and rhythmic contractions. However, it can occur in advanced-stage cancer patients and is detected with 7-30% prevalence in autopsy series. The most common primaries are melanoma (highest tropism), breast, lung, ovary, and colorectal cancer. It usually presents as part of widespread metastatic disease; isolated splenic metastasis is quite rare and relatively more common in ovarian carcinoma. Imaging shows multiple solid lesions, heterogeneous enhancement, necrosis, and cystic degeneration. Splenomegaly may accompany but is not as prominent as in lymphoma. Prognosis is generally poor as it indicates widespread disease.
Age Range
40-80
Peak Age
60
Gender
Equal
Prevalence
Uncommon
Metastasis to the spleen occurs through three pathways: (1) hematogenous spread (most common — tumor cells reach the spleen via arterial blood flow), (2) direct invasion (from adjacent organs — pancreatic tail, left kidney, left colon), (3) peritoneal spread (in ovarian, gastric, colon cancers). The spleen's resistance to metastasis is explained by multiple mechanisms: reticuloendothelial system (RES) macrophages in splenic sinusoids phagocytose circulating tumor cells; rhythmic contractions of the spleen prevent tumor cell adhesion; and lymphoid tissue-derived immune surveillance exerts antitumor effects. Therefore, splenic metastasis is usually seen with widespread disease that has overwhelmed the immune system. Melanoma shows the highest tropism to the spleen — integrins and chemokine receptors on melanoma cell surfaces provide strong adhesion to splenic sinusoidal endothelium. Heterogeneous enhancement on imaging reflects the irregular vascular architecture of neoangiogenesis; necrosis results from insufficient nutrition of rapidly growing tumor. Cystic degeneration is seen particularly in mucinous primaries (ovary, colon) or melanoma.
In a patient with known malignancy history, heterogeneously enhancing, irregularly marginated solid lesions with necrotic/cystic areas in the spleen are highly suggestive of metastasis. In melanoma, T1 hyperintense lesions are near-pathognomonic.
In the portal venous phase, solid lesions are seen that are hypodense relative to splenic parenchyma with heterogeneous enhancement. Margins are generally irregular or lobulated. Internal necrosis or cystic degeneration is common — a pattern of central hypodense necrotic area with peripheral enhancing viable tumor tissue ('rim enhancement') may be observed. In large lesions, exophytic component and capsular disruption may be seen. Unlike lymphoma, heterogeneity is prominent and lesions show more aggressive morphology.
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Multiple heterogeneously enhancing, irregularly marginated solid lesions are seen in the spleen with internal necrotic/cystic areas; in the context of known malignancy, consistent with metastatic involvement.
Metastases from hypervascular primary tumors (melanoma, RCC, thyroid carcinoma, neuroendocrine tumor) show prominent enhancement in the arterial phase. Melanoma metastasis is most commonly seen in a hypervascular pattern and may be difficult to recognize against the background of the spleen's normal heterogeneous zebra pattern enhancement. Metastases from hypovascular primaries (breast, lung, colon) show minimal enhancement in the arterial phase and are more conspicuous in the portal venous phase. Lesion-parenchyma contrast difference in the arterial phase varies according to the primary tumor vascularity.
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Prominently enhancing hypervascular lesions are seen in the spleen in the arterial phase, consistent with hypervascular metastases in the context of known melanoma/RCC.
In melanoma metastases, lesions show hyperintense signal on T1-weighted MRI relative to splenic parenchyma — this results from the paramagnetic properties of melanin pigment and is highly characteristic of melanoma metastasis. Amelanotic melanoma metastases do not show this feature. Metastases from other primaries generally show hypointense or isointense signal on T1. Hemorrhagic metastases may also be T1 hyperintense (methemoglobin) — clinical context is important for differentiation from melanoma.
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The splenic lesions show hyperintense signal on T1-weighted MRI, in the context of known melanoma history suggesting melanoma metastasis with paramagnetic T1 shortening due to melanin content.
On DWI, metastatic lesions show variable degrees of diffusion restriction — ADC values vary depending on primary tumor type and cellularity level. Solid viable tumor areas show diffusion restriction while necrotic/cystic areas show increased diffusion (high ADC). This heterogeneous DWI pattern distinguishes from the homogeneous diffusion restriction of lymphoma. Melanoma and high-grade tumor metastases show marked restriction.
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The splenic lesions demonstrate heterogeneous diffusion restriction on DWI with marked restriction in solid components and increased diffusion in necrotic areas.
On T2-weighted MRI, metastatic lesions show heterogeneous signal — solid components are mildly to moderately hyperintense, necrotic/cystic areas markedly hyperintense, hemorrhagic areas hypointense. This heterogeneous T2 pattern distinguishes from hemangioma's homogeneous marked hyperintensity and lymphoma's homogeneous mild hyperintensity. In melanoma metastases, the paramagnetic effect of melanin pigment causes T2 shortening → hypointense or mixed signal on T2 (T1 hyperintense + T2 hypointense = melanin effect).
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The splenic lesions show heterogeneous signal on T2-weighted MRI with solid, necrotic, and hemorrhagic components creating a mixed signal pattern.
On B-mode US, metastatic lesions show variable echogenicity — most are hypoechoic while some may show target pattern ('target sign' — hypoechoic halo surrounding hyperechoic center or vice versa), cystic components, or mixed echogenicity. Melanoma metastases may be hypoechoic or anechoic (cystic appearance). Margins are generally irregular. Splenomegaly accompanies variably. US sensitivity is limited for small (<1 cm) lesions.
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Multiple irregularly marginated, mixed echogenicity solid lesions are seen in the spleen on US; consistent with metastatic involvement in the context of known malignancy.
On FDG PET-CT, metastatic lesions generally show increased FDG uptake but SUVmax values vary according to primary tumor type. Melanoma and lung adenocarcinoma show high SUVmax while mucinous and well-differentiated tumors may show low uptake. PET-CT is superior to CT in detecting small lesions and concomitant metastatic involvement in other organs. SUVmax change is important in treatment response evaluation.
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Lesions showing increased metabolic activity are seen in the spleen on FDG PET-CT, consistent with splenic metastasis in the context of widespread metastatic disease.
Criteria
Highest splenic tropism. Hypervascular. T1 hyperintense (melanin). Cystic degeneration may occur.
Distinct Features
Hyperintense signal on T1-weighted MRI due to paramagnetic melanin — diagnostic. Amelanotic form lacks this feature. Multi-organ involvement common.
Criteria
Hypovascular pattern. Solid or mixed. Seen in advanced-stage disease.
Distinct Features
More conspicuous hypodense lesions in portal venous phase. Lobular carcinoma may show diffuse infiltration (splenomegaly without focal lesions).
Criteria
Peritoneal spread with implantation on splenic capsule. Ascites accompanies. CA-125 elevated.
Distinct Features
Capsular surface 'scalloping' and omental cake pattern may accompany. Isolated splenic metastasis is relatively more common in ovarian cancer.
Distinguishing Feature
Lymphoma is homogeneous, well-marginated with minimal enhancement, necrosis generally absent; metastasis is heterogeneous, irregularly marginated with necrotic areas.
Distinguishing Feature
Abscess shows rim enhancement, internal fluid/gas level, and homogeneous diffusion restriction on DWI; metastasis shows solid component and heterogeneous enhancement. Fever and leukocytosis expected in abscess.
Distinguishing Feature
Angiosarcoma is a primary splenic tumor presenting with hemorrhage and spontaneous rupture; metastasis is evaluated in the context of known primary tumor. In angiosarcoma, widespread liver metastases develop early.
Distinguishing Feature
Hemangioma shows peripheral nodular enhancement with centripetal fill-in (complete filling in delayed phase); metastasis shows heterogeneous enhancement with necrosis, no centripetal fill-in pattern.
Urgency
urgentManagement
medicalBiopsy
Not NeededFollow-up
specialist-referralSplenic metastasis is usually part of widespread metastatic disease with poor prognosis. Treatment is determined by primary tumor and disease extent — systemic chemotherapy, immunotherapy, or targeted therapy. Splenectomy may be curative in isolated splenic metastasis (especially ovarian cancer). Biopsy is generally not needed as imaging findings are diagnostic with known primary tumor; however, percutaneous biopsy may be considered in atypical presentations. PET-CT is critical for staging and treatment response evaluation.
Splenic metastasis is usually part of widespread metastatic disease and indicates poor prognosis. Isolated splenic metastasis is very rare, and splenectomy may be considered.