A 72-year-old woman from Mumbai with a history of hypertension and diabetes presents with progressive bilateral visual field loss over 3 weeks. She reports difficulty reading and bumping into objects on both sides. On perimetry, there is a bitemporal hemianopia with superior temporal quadrantanopia on the left and inferior temporal quadrantanopia on the right. MRI brain with contrast shows a 2 cm sellar mass compressing the optic chiasm from below. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Pituitary Adenoma ### Key Clinical Features **Key Point:** A sellar mass compressing the optic chiasm **from below** causing **bitemporal hemianopia** in a 72-year-old woman with hypertension and diabetes is most consistent with a **pituitary adenoma** — the single most common sellar mass in adults. ### Why Pituitary Adenoma, Not Craniopharyngioma? | Feature | Pituitary Adenoma | Craniopharyngioma | |---------|-------------------|-------------------| | **Prevalence** | Most common sellar tumor in adults (~80% of sellar masses) | 2nd most common non-pituitary sellar tumor | | **Age** | 40–70 yrs (any adult age) | Bimodal: 5–14 yrs & 50–75 yrs | | **Location** | Intrasellar, expands upward | Suprasellar (Rathke's pouch remnant) | | **Compression direction** | From below (upward on chiasm) | Typically suprasellar — from above or below depending on growth | | **Imaging** | Sellar mass, homogeneous/heterogeneous enhancement, no calcification | Cystic ± solid, **calcification in 90%** (key differentiator) | | **Endocrine dysfunction** | Very common (prolactin ↑, GH ↑, ACTH ↑, or hypopituitarism) | Less common initially | | **VF pattern** | Bitemporal hemianopia (inferior temporal quadrantanopia first with inferior compression) | Similar, but calcification on imaging is the distinguishing feature | ### Chiasmal Compression Mechanics **High-Yield:** The optic chiasm receives compression from a sellar mass **from below**, pushing it upward: - **Inferior nasal fibers** (representing superior temporal visual field) cross in the **inferior chiasm** → compressed first → **inferior temporal quadrantanopia** bilaterally - As the mass enlarges → full **bitemporal hemianopia** The asymmetric quadrantanopia pattern in this vignette (superior temporal left, inferior temporal right) reflects the variable and asymmetric nature of chiasmal compression seen in **pituitary adenoma** as it expands eccentrically — a well-recognized clinical phenomenon (Kanski's Clinical Ophthalmology, 9e). ### Why the Other Options Are Less Likely - **B) Craniopharyngioma**: Although it can present similarly, the MRI description lacks the hallmark **calcification (90%)** and cystic component. Craniopharyngioma is far less common than pituitary adenoma in adults. Without calcification on imaging, pituitary adenoma is the default diagnosis for a sellar mass compressing the chiasm from below. - **C) Optic chiasm glioma**: Intrinsic to the chiasm; causes enlargement of the chiasm on MRI, not a discrete sellar mass. Typically presents in children with NF-1. - **D) Meningioma of tuberculum sellae**: Compresses the chiasm **from above** (downward), causing **superior temporal quadrantanopia** first. Dural attachment and hyperostosis are imaging hallmarks. ### Clinical Pearl **Clinical Pearl:** Pituitary adenoma is the **most common cause of bitemporal hemianopia** in adults. Even in the absence of overt endocrine symptoms (non-functioning adenomas account for ~30% of pituitary adenomas), a sellar mass on MRI compressing the chiasm from below should be considered a pituitary adenoma until proven otherwise. Non-functioning macroadenomas often present with visual field defects as the first symptom precisely because they lack hormonal clues. ### Management **Key Point:** Management of pituitary macroadenoma with chiasmal compression: 1. **Transsphenoidal surgery**: First-line for non-functioning adenomas with visual compromise 2. **Dopamine agonists** (cabergoline/bromocriptine): First-line for prolactinomas 3. **Endocrine workup**: Prolactin, GH/IGF-1, ACTH/cortisol, TSH, LH/FSH 4. **Post-operative MRI**: Surveillance for residual/recurrent tumor 5. **Visual field monitoring**: Perimetry pre- and post-operatively [cite: Kanski's Clinical Ophthalmology 9e Ch 12; Harrison's Principles of Internal Medicine 21e Ch 375; Neuro-Ophthalmology by Burde, Savino & Trobe]