CLINICAL DISCUSSION:
Isolated splenic metastasis from colorectal cancer is rare, and most commonly occurs as a component of disseminated disease. Studies have shown that isolated splenic metastasis accounts for less than 1% of all splenic metastases (9). The incidence of splenic metastasis was reported as 7.1 % among 7165 autopsy by Breger with 4.4 % for colorectal carcinoma (10). Other causes of splenic metastasis are melanoma (34%), breast (12%), ovarian (12%), and lung (9%) cancers (2).
The rarity of solitary splenic metastasis from colorectal cancer has been attributed to several anatomical and immunological factors. Firstly, the acute angulation at the entry of the splenic artery at its origin in the celiac trunk may act as an anatomical obstruction for tumor emboli to reach the spleen (11). Additionally, the rhythmic contractions of the spleen could prevent tumor cell fixation by forcing blood flow from the sinusoids to the splenic veins(12). The absence of afferent lymphatics to the spleen and anticancer cytokines released by the spleen are also considered to be factors for the low incidence of metastasis(13). Furthermore, the reticuloendothelial system inhibits the aggregation of the nest of cancer cells in splenic sinusoids (14). Vascular and lymphatic route of transmission of splenic metastasis has been proposed for colorectal cancer .It is believed that vascular transmission is the primary route for the development of splenic metastasis, because the metastasis is reported to be located within the splenic parenchyma, with the lymph nodes at the hilus negative for metastasis in majority of case (10,15,16) .It is hypothesized that probably because of reflux of blood from the inferior mesenteric vein in the splenic vein and then to the spleen is responsible for cancer cells to reach the splenic parenchyma. This is in relation to the localization of the primary tumor to the left hemicolon in the majority of the patients with splenic metastasis (17) .In our case, the primary tumor was in the sigmoid colon which is similar to literatures which suggest left hemicolon as a frequent site.
Since most cases of splenic metastasis are asymptomatic, they are often discovered incidentally during imaging studies such as abdominal ultrasound or CT scans that are performed during routine follow-up visits for cancer patients (4).In our case , a follow-up CT scan performed two years found metastasis in the spleen. However, in some cases, patients may present with symptoms such as pain or discomfort in the upper abdomen, weight loss, or enlarged spleen. In rare cases, splenic metastasis can lead to spontaneous splenic rupture, which is a life-threatening emergency.
The preferred treatment for isolated splenic metastasis is considered to be splenectomy followed by chemotherapy(18). Long-term survival rate following splenectomy in patients with solitary splenic metastasis from colorectal cancer is still unknown. However, the limited data extracted from the case reports in the literature indicate that interval survival following splenectomy ranged from 3 to 84 months, with a mean of 22.5 months(6). The present case is disease-free during the one-month follow up.