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# T4–T5 nucleus

The nucleus pulposus is the soft, gel-like centre of the [T4-T5](https://durgical.com/en/anatomy/t4-t5/) disc in the mid-back; it works like a water cushion that spreads the load.

Official name: T4-T5

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## What it is

The soft, gel-like centre (nucleus pulposus) of the T4–T5 disc.

## What it does

Works like a water cushion: it turns pressure from above into outward push on the fibre ring, spreading the load. It is under the most pressure when you bend forward and lift.

## Key points

- Sits at the level of the sternal angle; a posterolateral fragment reaches the T4 root (the [nipple](https://durgical.com/en/anatomy/nipple/) band)

## Key facts

**Where**
Centre of the T4–T5 disc, slightly toward the back, inside the annulus fibrosus

**Function**
Notochord-derived gel (about 70–90% water, proteoglycans); turns axial load into annulus tension; small in thin thoracic discs, herniation rare

## Relations

**Behind**
Back of the annulus fibrosus and the [posterior longitudinal ligament](https://durgical.com/en/anatomy/posterior-longitudinal-ligament/), then the [spinal cord](https://durgical.com/en/anatomy/spinal-cord/)

## On imaging

Axial MRI at this level also shows the carina and the azygos arch in front of the [spine](https://durgical.com/en/anatomy/region/spine/), a useful check that the level is right.

## Common problems

- Squeezes out through a tear in the ring (herniation), usually backward and to one side, toward a nerve root.
- Loses water with age, so the disc gets thinner and stiffer.

## How it is diagnosed

On MRI a healthy nucleus is bright on T2 images; a worn one turns dark ('black disc').

## Treatment

- In a microdiscectomy only the loose piece that has pushed out is removed; most of the disc stays.

## Clinical notes

- Pain between the shoulder blades with no clear band is a common first symptom of mid-thoracic disc disease and is easily blamed on the muscles
- Mid-thoracic pain with weight loss or night pain in an older adult suggests a metastasis rather than a disc; on imaging, tumour tends to spare the disc space while infection destroys it

## Development

The thoracic curve is a primary curve kept from the flexed fetal posture. Unlike the neck and low back, where wedge-shaped discs build the curve, the thoracic discs are of fairly even height and the curve comes mainly from the bodies.

## Test yourself

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

## Which surface landmark lies at the level of the T4–T5 nucleus?

The sternal angle.

## Which root and dermatome can a posterolateral fragment of the T4–T5 nucleus reach?

The T4 root, the nipple band.

## On axial MRI, which structures in front of the spine confirm the T4–T5 level?

The carina and the azygos arch, a useful check that the level is right.

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Educational information, not medical advice. For any symptom, see a health professional.

## Its names

**Official Latin (TA2)**
nucleus pulposus T4-T5 TA2 1686

**Official Spanish (DeCS)**
Núcleo pulposo T4-T5 DeCS D000070614

**English (TA2)**
T4-T5

## Related

- [T4–T5 disc](https://durgical.com/en/anatomy/t4-t5/)
- [T4 vertebra](https://durgical.com/en/anatomy/t4/)
- [T5 vertebra](https://durgical.com/en/anatomy/t5/)

Sources: Terminologia Anatomica (TA2); [DeCS](https://decs.bvsalud.org/es/ths/resource/?id=56248&filter=ths_termall&q=N%C3%BAcleo%20Pulposo); [Anatomy, Back, Nucleus Pulposus](https://www.ncbi.nlm.nih.gov/books/NBK535373/); [Anatomy, Back, Intervertebral Discs](https://www.ncbi.nlm.nih.gov/books/NBK470583/); [7.3 The Vertebral Column](https://openstax.org/books/anatomy-and-physiology-2e/pages/7-3-the-vertebral-column) (OpenStax (Rice University), 2022) · adapted, [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/); Anatomy of the Human Body (20th ed.): Articulations of the Vertebral Column (Lea & Febiger (Gray's Anatomy, 1918), 1918) · adapted, Public domain.

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/anatomy/t4-t5-spine-and-pelvis/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/t4-t5-spine-and-pelvis/