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# Lactotroph PitNET (prolactinoma)

- Lesion

A prolactinoma makes too much prolactin, so periods stop and the breasts leak milk. Not every high prolactin is a tumour.

Updated Nov 12, 2026

## Key points

- Commonest functioning PitNET; women present earlier with microadenomas, men later with macroadenomas.
- Prolactin is the only pituitary hormone under tonic inhibition (by dopamine), so stalk damage raises it: the stalk effect.
- Other causes of high prolactin: pregnancy, dopamine-blocking drugs (antipsychotics, metoclopramide), primary hypothyroidism (TRH stimulates prolactin), kidney failure.
- Morphology: chromophobic, sparsely granulated cells; psammoma-like calcification can occur (the «pituitary stone»).
- Dopamine agonists shrink the tumour and reduce prolactin; treated tumours show small cells and fibrosis.

## What it is

Lactotroph tumours are the most frequent hormone-producing pituitary tumours. Prolactin excess suppresses gonadotropin-releasing hormone, so women have amenorrhoea, galactorrhoea and infertility, and men have low libido and erectile dysfunction. The serum prolactin level roughly tracks tumour size, and these tumours usually shrink with dopamine agonists, so most are treated medically.

## Structure

- Usually a microadenoma in women and a macroadenoma in men.
- H&E: chromophobic cells, often sparsely granulated, with juxtanuclear prolactin staining (Golgi pattern).
- Calcification, sometimes extensive, can turn the tumour into a small stone.
- After dopamine agonist therapy: smaller cells with shrunken nuclei and interstitial fibrosis.

## Step by step

- A PIT1-lineage clone of lactotrophs grows autonomously.
- It secretes prolactin regardless of hypothalamic dopamine.
- High prolactin suppresses hypothalamic GnRH pulses.
- LH and FSH fall: anovulation and amenorrhoea in women, low testosterone in men.
- Prolactin also acts on the breast, causing galactorrhoea; large tumours add mass effects.

## High prolactin: tumour or not

| Cause | Mechanism | Clue |
| --- | --- | --- |
| [Lactotroph PitNET](https://durgical.com/en/conditions/prolactinoma/) | Autonomous secretion | Level rises with size; tumour on imaging |
| [Stalk compression (any sellar mass)](https://durgical.com/en/conditions/pituitary-adenoma/) | Dopamine cannot reach lactotrophs | Modest rise with a large non-lactotroph mass |
| Dopamine-blocking drugs | Receptor blockade | History of antipsychotic or antiemetic use |
| [Primary hypothyroidism](https://durgical.com/en/conditions/hypothyroidism/) | TRH stimulates lactotrophs | High TSH, low free T4 |
| Pregnancy and breastfeeding | Oestrogen-driven lactotroph hyperplasia | Physiological |
| [Chronic kidney disease](https://durgical.com/en/conditions/chronic-kidney-disease/) | Reduced clearance | Raised creatinine |

## Clinical notes

- Women: secondary amenorrhoea, galactorrhoea, infertility; men: headache, visual loss, low libido, sometimes gynaecomastia.
- Long-standing hypogonadism lowers bone density.
- Lactotroph tumours are the commonest pituitary tumour in MEN1.

## Memory aid

Dopamine is the leash on prolactin: cut the stalk and the dog runs free, so any big sellar mass can raise prolactin a little.

## Test yourself

Think of the answer, then tap the question to see it.

## Why can a non-functioning pituitary macroadenoma raise prolactin?

By compressing the stalk it blocks dopamine from reaching lactotrophs, removing their tonic inhibition (stalk effect).

## How does primary hypothyroidism raise prolactin?

Low thyroid hormone raises hypothalamic TRH, which also stimulates lactotrophs to secrete prolactin.

## Why does prolactin excess cause amenorrhoea?

It suppresses pulsatile GnRH release, so LH and FSH fall and ovulation stops.

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## Elsewhere in DurgiPedia

- [Prolactin and its control by dopamine](https://durgical.com/en/physiology/prolactin-and-its-control-by-dopamine/)
- [Pathologic calcification: dystrophic vs metastatic](https://durgical.com/en/general-pathology/pathologic-calcification-dystrophic-vs-metastatic/)

## Connections

## Related 3

- [Pituitary neuroendocrine tumours (PitNETs): overview](https://durgical.com/en/general-pathology/pituitary-neuroendocrine-tumours-overview/)
- [Somatotroph PitNET: gigantism and acromegaly](https://durgical.com/en/general-pathology/somatotroph-pitnet-gigantism-and-acromegaly/)
- [Multiple endocrine neoplasia (MEN) syndromes](https://durgical.com/en/general-pathology/multiple-endocrine-neoplasia-syndromes/)

## Related conditions 5

- [Prolactinoma (hyperprolactinaemia)](https://durgical.com/en/conditions/prolactinoma/)
- [Pituitary adenoma](https://durgical.com/en/conditions/pituitary-adenoma/)
- [Hypothyroidism](https://durgical.com/en/conditions/hypothyroidism/)
- [Male hypogonadism](https://durgical.com/en/conditions/male-hypogonadism/)
- [Multiple endocrine neoplasia (MEN 1, 2A, 2B)](https://durgical.com/en/conditions/multiple-endocrine-neoplasia/)

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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Pituitary Adenoma](https://www.ncbi.nlm.nih.gov/books/NBK554451/) (StatPearls (NCBI Bookshelf), 2025); [Pituitary Tumors Treatment (PDQ®)–Health Professional Version](https://www.cancer.gov/types/pituitary/hp/pituitary-treatment-pdq) (National Cancer Institute, 2025).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/general-pathology/lactotroph-pitnet/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/lactotroph-pitnet/