Pituitary Macroadenoma MCQ — NEET PG Practice Question | NEETPGAI
Pituitary Macroadenoma
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microscope Pathology
A 42-year-old woman presents with 8 months of progressive bilateral peripheral vision loss, secondary amenorrhea, galactorrhea, and headaches. Visual field testing confirms bitemporal hemianopia. Serum prolactin is 850 ng/mL. MRI shows a 1.8 cm sellar mass with suprasellar extension. The structure marked **A** in the diagram represents the sellar tumor with suprasellar extension. Which of the following best describes the mechanism by which this lesion produces the patient's visual field defect?
A. Compression of the optic nerves at the orbital apex causing monocular vision loss
B. Compression of the optic chiasm causing bitemporal hemianopia from pressure on decussating nasal retinal fibers
C. Compression of the lateral geniculate nucleus leading to homonymous hemianopia
D. Compression of the optic radiations in the temporal lobe causing superior quadrantanopia
Explanation
Why "Compression of the optic chiasm causing bitemporal hemianopia from pressure on decussating nasal retinal fibers" is right
Pituitary macroadenomas with suprasellar extension (marked A) grow upward through the diaphragma sellae and directly compress the optic chiasm from below. The decussating nasal retinal fibers—which cross at the chiasm to represent the contralateral temporal visual fields—are compressed first, producing the classic bitemporal hemianopia. This is the pathognomonic mass effect sign of sellar pathology. The patient's visual field testing confirms this mechanism. Per WHO Pituitary Tumor Classification 2022 and Endocrine Society guidelines, bitemporal hemianopia is the hallmark visual complication of suprasellar extension in pituitary macroadenomas.
Why each distractor is wrong
Compression of the lateral geniculate nucleus leading to homonymous hemianopia: The lateral geniculate nucleus is located in the thalamus, far posterior to the sella turcica. Pituitary adenomas do not extend posteriorly to compress this structure; they compress the chiasm anteriorly.
Compression of the optic nerves at the orbital apex causing monocular vision loss: The optic nerves are located lateral and anterior to the sella turcica. Pituitary adenomas compress the chiasm at the sella, not the orbital apex nerves; monocular loss would indicate a unilateral lesion, not the bilateral bitemporal pattern seen here.
Compression of the optic radiations in the temporal lobe causing superior quadrantanopia: The optic radiations are deep intracranial structures far removed from the sella turcica. Pituitary adenomas do not extend into the temporal lobe; they compress the chiasm at the level of the sella.
High-YieldNEET PG
Suprasellar extension of pituitary macroadenomas → bitemporal hemianopia from chiasmal compression of decussating nasal fibers. This is the classic mass effect sign distinguishing sellar from other CNS lesions.
Endocrine Society Clinical Practice Guidelines; WHO Pituitary Tumor Classification 2022
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