**Core Concept**
Electroconvulsive therapy (ECT) is a psychiatric treatment that involves the use of electrical impulses to induce seizures in patients with severe mental illnesses, such as major depressive disorder or schizophrenia. However, its application is restricted due to certain absolute contraindications that pose significant risks to the patient.

**Why the Correct Answer is Right**
A brain tumor is an absolute contraindication to ECT because it may exacerbate the condition, leading to increased intracranial pressure, brain herniation, or even rupture of the tumor. This is particularly concerning in patients with space-occupying lesions, such as glioblastomas or metastatic brain tumors, where the risk of complications is significantly higher. ECT can cause a sudden increase in intracranial pressure, which may be catastrophic in the presence of a brain tumor.

**Why Each Wrong Option is Incorrect**
**Option A:** Glaucoma is not an absolute contraindication to ECT, although patients with glaucoma may require careful monitoring of their intraocular pressure during treatment. **Option D:** Myocardial infarction (MI) is a relative contraindication to ECT, and patients should be stabilized before undergoing treatment. **Option C:** Aortic aneurysm is not typically considered a contraindication to ECT, unless the aneurysm is ruptured or unstable.

**Clinical Pearl / High-Yield Fact**
It is essential to obtain a thorough medical history and perform a comprehensive physical examination before administering ECT, as this can help identify potential contraindications and ensure patient safety.

**✓ Correct Answer: B. Brain tumor**