**Core Concept**
Psychosurgery, also known as neurosurgical psychosocial intervention, involves the surgical alteration of brain tissue to treat severe psychiatric disorders. This invasive procedure is typically considered for patients with severe, treatment-resistant mental illnesses, such as intractable depression, obsessive-compulsive disorder, and certain cases of schizophrenia.

**Why the Correct Answer is Right**
The correct answer involves the use of psychosurgery in the treatment of severe, treatment-resistant mental illnesses. This is because psychosurgery targets specific neural circuits involved in these disorders, such as the anterior cingulate cortex and the orbitofrontal cortex. The procedure aims to alleviate symptoms by disrupting abnormal neural activity patterns.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect, as psychosurgery is not typically indicated for patients with substance use disorders. While some patients with substance use disorders may also have co-occurring mental illnesses, psychosurgery is not a standard treatment for substance use disorders themselves.

**Option B:** Incorrect, as psychosurgery is not usually indicated for patients with anxiety disorders. While some patients with anxiety disorders may benefit from other forms of neurosurgical intervention, psychosurgery is not a standard treatment for these conditions.

**Option C:** Incorrect, as psychosurgery is not typically indicated for patients with personality disorders. While some patients with personality disorders may benefit from other forms of psychotherapy or psychopharmacological treatment, psychosurgery is not a standard treatment for these conditions.

**Clinical Pearl / High-Yield Fact**
Psychosurgery should be considered a last resort for patients with severe, treatment-resistant mental illnesses, and the decision to proceed should be made after thorough evaluation and discussion with the patient and their family.

**Correct Answer: D. Treatment-resistant schizophrenia.**