A 65-year-old man presented to the Emergency Department with sudden left side weakness and a mild headache. There were no other symptoms, such as flank or abdominal pain, nausea, and vomiting. The patient had a medical history of chronic obstructive pulmonary disease and asthma. He had no history of coronary artery disease or cerebrovascular accident, and there was no family history of brain disease. Complete blood count, blood urea nitrogen, creatinine, electrolytes, and liver function test findings were within normal ranges. On physical examination, vital signs were stable. The patient had decreased motor and sensory responses in the left upper and lower limbs, compared with the right side. Dysphagia was observed but orientation was not impaired. The patient had previously undergone a robot-assisted laparoscopic radical nephrectomy for RCC, approximately 15 months prior (Fig. 1). The tumor size was 9.5 cm×7.0 cm×6.5 cm. The tumor extended up to renal sinus fat but not beyond Gerota's fascia. The pathological stage was T3a according to the 8th edition of the cancer staging system established by the American Joint Committee on Cancer. The final histopathological diagnosis was clear-cell type RCC with Fuhrman nuclear grade 4. Resection margins were negative. Immunohistochemical analysis revealed that the tumor tissue was positive for CD10 and negative for cytokeratin 7 (Fig. 2). The patient was discharged on the fifth postoperative day without any complications. Follow-up abdominal and chest computed tomography (CT) scans were performed at 6-month intervals. Preoperatively, the patient had a 3-mm intrapulmonary lymph node or inflammatory nodule in the left upper lung on chest CT, which could not be excluded as a metastatic nodule. However, the nodule disappeared spontaneously during the follow-up period (Fig. 3). There was no evidence of metastasis until the patient presented to the Emergency Department with neurological symptoms. Brain CT and magnetic resonance imaging (MRI) revealed a 2.5-cm high-attenuated mass in the right temporal lobe with perilesional edema (Fig. 4). Navi gation-guided surgery was performed by the neurosurgery department to remove the mass that was causing the symptoms. Histological analysis of the specimen revealed findings identical to the original RCC. Resection margins were negative. Immunohistochemical analysis revealed that the tumor tissue was positive for CD10 and PAX-8 (Fig. 5). After surgery, whole-body positron emission tomography/CT (PET- CT) was performed for RCC restaging workup; no evidence of metastasis was found elsewhere. One month after the surgery, the patient underwent adjuvant chemotherapy with pazopanib, a tyrosine kinase inhibitor. Follow-up brain CT and MRI scans were performed 3 months after surgery. Postoperative hemorrhagic fluid collection and perilesional edema were almost completely resolved (Fig. 6). After 6 months, the patient had no neurological symptoms and there was no further evidence of metastasis on imaging.

Informed written consent was obtained from the patient for publication of this report and any accompanying images.

Brain metastases from RCC occur in approxi- mately 3.9%-24% of affected patients; the mean interval between nephrectomy and brain metastasis is 1-3 years.^4,7 The prognoses for patients with single or multiple RCC brain metastases are poor and mortality rates are high. The mean survival time after diagnosis is less than 1 year, and the median survival time is 3-4 months without treatment.⁸

Some current systems may help to estimate the survival rates in RCC patients. The University of California, Los Angeles Integrated Scoring System stratifies patients into 3 risk categories based on pathological stage, nuclear grade, and Eastern Cooperative Oncology Group performance status.⁹ The stage, size, grade, and necrosis risk score uses tumor stage, size (>5 cm), nuclear grade, and tumor necrosis to determine a risk score associated with recurrence in clear-cell RCC patients.¹⁰ In our patient, the mass was larger than 7 cm, extended to the renal sinus (T3a), and had a Fuhrman nuclear grade of 4. The Eastern Cooperative Oncology Group performance score was 0. The patient was classified as intermediate risk using the University of California, Los Angeles Integrated Scoring System.

Isolated RCC brain metastases are rare. In most patients, RCC involves adjacent organs first (e.g., lungs, regional lymph nodes, bone, and liver). RCC is also more likely to cause multiple metastases. The 2021 National Comprehensive Cancer Network guidelines recommend performing abdominal- pelvic CT or MRI, as well as chest radiography. However, bone scans, chest CT scans, and brain MRI scans are recommended if clinically indicated. The cost-effectiveness of these investigations has not been established thus far. Therefore, screening tests are not routinely performed.

The main treatment options for RCC brain metastases include local aggressive treatments, such as complete surgical resection, stereotactic radiosurgery, or a combination. Complete surgical resection is the treatment of choice in patients with surgically accessible tumors. Surgery provides the best outcomes because it can confirm pathological findings and provide immediate symptomatic relief. It is important to differentiate between these conditions to achieve better survival outcomes. In our patient, the brain mass was completely resected, and the diagnosis was histopathologically confirmed, providing further guidance for treat- ment decisions.

We hypothesized that the patient already had a brain metastasis at the time of initial diagnosis, but it remained undetected because brain-re- lated screening tests were not performed. Alter- natively, the patient might have developed late hematogenous recurrence after surgery. In either situation, it would be meaningful to perform additional tests (e.g., CT scans, MRI scans, bone scans, and PET-CT scans) in patients with a high pathologic T-stage or a high nuclear grade, regardless of symptoms.

In conclusion, during RCC follow-up, careful review of the patient's history and physical exa- mination are important. As demonstrated in this report, patients with large renal masses or intermediate to high recurrence risk scores may benefit from additional investigations, regardless of symptoms. Further well-designed studies are needed to establish cost-effectiveness of routine brain investigations.