We present the case of a 71-year-old man who was diagnosed with amoebic encephalitis caused by Balamuthia mandrillaris. He had rheumatic arthritis for 30 years and had undergone continuous treatment with immunosuppressants. First, he complained of partial spasm from the left thigh to the left upper limb. Magnetic resonance imaging revealed multifocal enhancing nodules in the cortical and subcortical area of both cerebral hemispheres, which were suggestive of brain metastases. However, the patient developed fever with stuporous mentality and an open biopsy was performed immediately. Microscopically, numerous amoebic trophozoites, measuring 20 to 25 µm in size, with nuclei containing one to four nucleoli and some scattered cysts having a double-layered wall were noted in the background of hemorrhagic necrosis. Based on the microscopic findings, amoebic encephalitis caused by Balamuthia mandrillaris was diagnosed. The patient died on the 10th day after being admitted at the hospital. The diagnosis of amoebic encephalitis in the early stage is difficult for clinicians. Moreover, most cases undergo rapid deterioration, resulting in fatal consequences. In this report, we present the first case of B. mandrillaris amoebic encephalitis with fatal progression in a Korean patient.

Pituitary adenoma is a common neuroendocrine tumor that accounts for approximately 17% of all primary intracranial neoplasms [1]. While most of these tumors are benign, some show aggressive patterns such as invasion into surrounding structures. In contrast to the functioning pituitary adenomas, which are usually quickly detected due to symptoms of excess hormone secretion, the detection of a non-functioning pituitary adenoma (NFPA) is relatively delayed. As a result, NFPAs are usually found as macroadenomas (1-4 cm) or giant adenomas (> 4 cm) with suprasellar extension (SSE), which tend to invade into the cavernous sinus. The effectiveness of hormone control therapy for NFPA is limited, and surgical removal is the only effective treatment [2,3]. Based on these aspects, it is clinically important to identify prognostic markers of NFPAs.In the 2004 World Health Organization (WHO) classification, three subcategories were proposed for the classification of primary pituitary tumors: typical, atypical, and carcinoma [4]. Atypical pituitary adenoma was diagnosed based on histopathological features, including a high Ki-67 proliferation index (> 3%), p53 expression, and a high mitotic count. However, as the WHO classification was revised in 2017, the term "atypical pituitary adenoma" is no longer recommended based on studies reporting that this subtype does not reflect prognosis [5][6][7]. Instead, histological or radiological invasiveness status has emerged as an important factor for predicting prognosis, which was also introduced in the 2017 WHO classification [5,8]. In general, two factors are predominantly used to evaluate the invasiveness status of pituitary adenoma: SSE and cavernous sinus invasion (CSI). CSI is directly associated with prognosis [9]. On the other hand, there are many studies indicating that SSE alone lacks prognostic