Sellar & Pituitary Lesions
- The sella is a tiny bony saddle holding the pituitary gland; lesions here punch way above their size because of the neighbors they squish.
- The single most useful question is "is this in the gland (sellar) or coming from above it (suprasellar)?" — it splits the differential before you've even thought hard.
- Pituitary adenoma is the overwhelmingly common sellar mass: macroadenomas push up and notch into a "snowman/figure-8," microadenomas are tiny and enhance less than the gland early.
- The structure you must protect — and report on — is the optic chiasm sitting right on top, plus the cavernous sinuses on either side.
- Pituitary apoplexy (sudden hemorrhage/infarction of the gland) is the emergency: thunderclap headache, vision loss, and a sick patient — don't sit on it.
The pituitary gland is roughly the size of a kidney bean, tucked into a little bony saddle at the base of the skull called the sella turcica (Latin for "Turkish saddle," because someone in anatomy clearly missed their horse). For something so small, it runs an absurd amount of the body's hormonal payroll. The catch: it lives in a cramped studio apartment with very important neighbors, so even a small lesion here causes loud problems. That crowding is the whole story of sellar imaging.
Location first: sellar vs suprasellar
Before you name anything, answer one question — is the lesion in the saddle (sellar) or floating above it (suprasellar)? This single fork does most of the diagnostic work, because the two compartments keep different company.
| Location | What you think of first |
|---|---|
| Sellar (in the gland) | Pituitary adenoma, far and away the most common. Then cysts, and rare things like hypophysitis. |
| Suprasellar (above) | Craniopharyngioma, meningioma, aneurysm, hypothalamic/optic glioma. |
An aneurysm of the internal carotid can masquerade as a suprasellar mass. Biopsying or operating on one because you called it a "tumor" is the kind of mistake that ends up in a textbook. Always look at the vessels — on MRI a flow void, on CTA the lit-up sac — before anyone reaches for a needle.
The star of the show: pituitary adenoma
If you see a mass arising from the gland, the smart money is on an adenoma. We split them by size, and the size genuinely changes how they look and behave.
A macroadenoma (1 cm or larger) outgrows the saddle and pushes upward. As it squeezes through the narrow opening at the top, it pinches in at the waist and balloons above — radiologists call it the "snowman" or figure-8 sign. Picture toothpaste forced through the gap in a not-quite-open cap. The danger is what it shoves into above: the optic chiasm drapes right over the sella, so an upward-growing mass classically steals your peripheral vision on both sides (bitemporal hemianopia, the "I keep clipping doorframes" complaint).
A microadenoma (under 1 cm) is the opposite hunt — a needle, not a haystack. It's a subtle nodule that, in the crucial early seconds after contrast, enhances less than the brightly enhancing normal gland around it. Blink and you'll miss it, which is why dedicated pituitary MRI uses thin slices and dynamic (timed) post-contrast imaging.
Why MRI, and what to look at
CT is great for showing the bony saddle remodeling and any calcification, and it's usually the first study a patient gets. But the gland, the chiasm, and the cavernous sinuses are soft-tissue questions, so the real work happens on MRI, with its ability to separate tissues by their T1 and T2 signal.
A couple of normal-anatomy anchors worth knowing so you don't cry wolf:
- The posterior pituitary is normally bright on T1 (the so-called "bright spot") — that's expected, not a lesion.
- The gland can be physiologically plump in young women and in pregnancy. Bigger isn't automatically a mass.
A common trap is the empty sella — the saddle looks "empty" because cerebrospinal fluid has herniated into it and flattened the gland against the floor. It's frequently an incidental, harmless finding. Don't report a normal variant as a missing or destroyed pituitary; follow the thin rim of squashed gland tissue along the floor and you'll find it.
The neighbors that turn a small lesion into a big deal
The sella's roommates are why this region is high-stakes. Laterally sit the cavernous sinuses, each carrying the internal carotid artery and several cranial nerves; a mass that invades sideways and wraps the carotid is much harder to resect. Above sits the chiasm and the floor of the third ventricle. A few specific entities lean on these relationships:
- Craniopharyngioma — a suprasellar mass famous for being part-cyst, part-solid, with calcification, especially in kids. Think "engine oil" cyst fluid and a lesion that loves to recur.
- Meningioma — arising from the dura around the sella, behaving like its cousins elsewhere in the brain: solid, avidly enhancing, often with a dural tail.
- Rathke cleft cyst — a benign cyst, usually quiet and incidental.
The one true emergency: apoplexy
Pituitary apoplexy is sudden hemorrhage or infarction within the gland (often a previously unknown adenoma). It presents like a thunderclap: severe headache, abrupt vision loss, eye-movement problems, and sometimes acute hormonal collapse. On imaging you're hunting for blood and swelling in an enlarged gland. This is the sellar finding you escalate immediately — the patient may need steroids and urgent neurosurgical input.
The takeaway
Sella imaging is a small box with loud consequences. Lock in the location (in the saddle vs above it), name the adenoma when the mass clearly comes from the gland, always glance at the chiasm above and the carotids beside, and never call an aneurysm a tumor. Do that, and the tiny saddle stops being intimidating.