A 35-year-old woman undergoes MRI brain for progressive headaches and visual disturbances. Imaging reveals a well-defined, intrasellar mass with suprasellar extension, homogeneous signal intensity, and marked enhancement on contrast administration. What is the most common histological type of sellar tumor in this presentation?

Explanation

## Most Common Sellar Tumor: Prolactin-Secreting Adenoma ### Epidemiology and Frequency **Key Point:** Prolactin-secreting adenomas (prolactinomas) account for approximately 40–50% of all pituitary adenomas, making them the most common functional pituitary tumor and the most common sellar mass overall [cite:Harrison 21e Ch 375]. ### Clinical and Imaging Features - **Presentation:** Amenorrhea, galactorrhea, infertility, and decreased libido in women; erectile dysfunction and gynecomastia in men. - **MRI characteristics:** Homogeneous, well-defined intrasellar mass with iso- to hypointense signal on T1 and hyperintense on T2; marked homogeneous enhancement post-contrast. - **Suprasellar extension:** Common when tumors exceed 10 mm, causing visual field defects (bitemporal hemianopsia) and headaches. ### Biochemical Confirmation **High-Yield:** Serum prolactin levels >200 ng/mL are virtually diagnostic of prolactinoma; levels 25–200 ng/mL require clinical correlation and exclusion of other causes (pregnancy, hypothyroidism, antipsychotics). ### Differential Diagnosis of Sellar Masses | Entity | Frequency | Key Features | Age Group | |--------|-----------|--------------|----------| | **Prolactinoma** | 40–50% | Homogeneous enhancement, suprasellar extension common | 20–40 years (F > M) | | **Non-functioning adenoma** | 25–30% | Often larger at presentation, incidental | 40–60 years | | **Craniopharyngioma** | 5–10% | Cystic/solid, calcification, suprasellar origin | Bimodal: 5–14 & 50–74 years | | **Meningioma** | 2–5% | Dural tail sign, hyperostotic bone, broad dural base | 40–70 years (F > M) | ### Clinical Pearl **Tip:** Dopamine agonists (bromocriptine, cabergoline) are first-line medical therapy for prolactinomas; surgery is reserved for dopamine-resistant tumors or apoplexy. This is why imaging confirmation is critical — the diagnosis guides management strategy. ### Why Prolactinoma Is Most Common 1. **Biological predisposition:** Lactotroph cells comprise ~15–20% of anterior pituitary; lactotroph adenomas arise most frequently. 2. **Symptomatic detection:** Hormonal effects (amenorrhea, galactorrhea) drive early clinical presentation and imaging workup. 3. **Incidental finding:** Prolactinomas are also the most common incidental pituitary adenoma on brain MRI.