Diagnostic Challenges in an Elderly Patient With Cognitive Decline and an Incidental Brain Mass.

Cognitive impairment in the elderly is often attributed to neurodegenerative processes such as dementia or delirium. However, in some cases, structural brain lesions, including malignancies like glioblastoma and lymphomas, can present similarly. This case report is of a 79-year-old male with progressive cognitive decline who was initially suspected to have dementia but was later found to have a brain mass. The absence of focal neurological deficits and a normal initial CT scan delayed the recognition of an underlying malignancy. An MRI ultimately revealed a lesion concerning glioblastoma or primary central nervous system lymphoma (PCNSL). Given the patient's frailty, the neuro-oncology multidisciplinary team (MDT) recommended best supportive care rather than an invasive biopsy. This case underscores the importance of thorough assessment and neuroimaging in cases of unexplained cognitive decline and highlights the diagnostic pitfalls that can lead to misdiagnosis.