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.