Brain metastases from CRC are uncommon, occurring in 0.4–5.4% of cases [2, 4]. The increasing incidence of brain metastases in patients with metastatic CRC has been attributed to the longer survival seen with newer systemic therapies [1, 5]. Thus, brain metastases are generally found as a part of systemic diseases. In addition, brain metastasis is generally considered to have a poor prognosis, with survival expectancy < 6 months. For example, Farnell et al. reported that the 1-year survival rate of patients with brain metastases is 16% after diagnosis, and the median survival time is 42 weeks after surgical resection plus postoperative radiotherapy [6,7,8].
As in our case, solitary brain metastasis detected prior to primary CRC diagnosis is very rare. Several cases have reported discovery of brain metastases before diagnosis of primary colonic cancer [9, 10]; however, only one case of isolated brain metastases has been reported [11].
Previous studies have suggested that there is a relationship between brain anatomy and brain metastasis [12, 13]. Brain metastasis preferentially arises at the cerebellum, gray–white matter junction, and watershed areas. In our case, the tumor was located near the surface of the left frontal lobe, which was one of the reasons why resection was chosen.
The primary approaches to the treatment of brain metastases include surgery, stereotactic radiosurgery, and whole-brain radiotherapy (WBRT). Important factors to consider in patients presenting with a single brain mass suspected of being a metastatic tumor include: tumor size and location; degree of mass effect and edema; presence or absence of symptoms; functional status and extent of systemic disease; and patient preferences with regard to invasive therapy. In the present case, neurosurgical resection was performed first, as a response to rapidly progressing neurological symptoms. The subsequent pathological diagnosis indicated CRC. Surgery is generally indicated for treatment of brain metastases if survival is expected to be at least a few months, if the tumor is resectable, and if other metastatic sites are under control. Furthermore, therapy after resection of brain metastases reduces intracerebral recurrence [14]. Here we performed postoperative WBRT, which controlled recurrence at the time this manuscript was accepted.
In our case, the patient received WBRT after brain metastasis resection, which is considered controversial [15]. Three randomized clinical trials have compared surgery plus WBRT with WBRT alone in patients with single brain metastases. Two of these demonstrated a survival benefit and indicated which patients can benefit from this combined approach, such as young patients and those with solitary brain metastasis, without extracranial metastasis, as in our case.
Recently, stereotactic irradiation of the brain tumor has been developed with local control rates of 80–90% [16]. Japanese guidelines recommend stereotactic irradiation when the number of brain metastases is no more than three or four and the maximum diameter of each metastasis does not exceed 3 cm [17]. In general, patients with brain metastases have a poor prognosis. Although the primary tumor is immediately resected after brain metastasis, new metastases may appear early in the course of the disease. If there are no symptoms related to the primary tumor, then systemic chemotherapy and follow-up may be considered. In our case, there were no symptoms related to the primary tumor, but since no evident metastasis was found in the systemic examination after brain tumor resection, we decided to perform surgery. In addition, the fact that the patient was taking anticoagulants was another reason for performing primary tumor resection immediately.
