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# Pyramidalis

The pyramidalis is a small triangular muscle just above the pubic bone, in front of the lower rectus abdominis; it tightens the midline of the belly.

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## What it is

A small triangular muscle in front of the lower rectus, missing in some people.

## What it does

Tenses the linea alba.

## Key points

- Lies inside the rectus sheath, in front of the lower rectus abdominis, below the arcuate line
- The pair of muscles marks the midline just above the pubis: in a Pfannenstiel incision they are separated to find the linea alba
- Of little functional importance; its absence causes no weakness

## Key facts

**Origin**
Pubic crest and pubic symphysis, in front of rectus abdominis (absent in about 20%)

**Insertion**
Linea alba, about midway between pubis and umbilicus

**Action**
Tenses the linea alba

**Nerve**
Subcostal nerve (T12) (some texts: also iliohypogastric or ilioinguinal, L1)

**Blood supply**
[Inferior epigastric artery](https://durgical.com/en/anatomy/inferior-epigastric-artery/)

## Relations

**In front**
Anterior layer of the [rectus sheath](https://durgical.com/en/anatomy/rectus-sheath/) (all three flat-muscle aponeuroses at this level), subcutaneous fat and [skin](https://durgical.com/en/anatomy/skin/)

**Behind**
Lower part of the [rectus abdominis](https://durgical.com/en/anatomy/rectus-abdominis-muscle/)

**Medial**
The pyramidalis of the other side, the two meeting at the [linea alba](https://durgical.com/en/anatomy/linea-alba/)

**Below**
Its base on the pubic crest and the front of the [pubic symphysis](https://durgical.com/en/anatomy/pubic-symphysis/)

## How to find it

It can't be felt. In a low transverse (Pfannenstiel) or lower midline approach, once the anterior rectus sheath is opened it appears as a small triangle of muscle above the pubis, its apex pointing up into the linea alba.

## On imaging

On ultrasound, CT or MRI it is a small triangle in front of the lower rectus abdominis; when only one side is present or the two differ in size, it should not be mistaken for a mass.

## Common problems

- Hernias: a weak spot lets fat or bowel bulge through (groin, belly button, old incisions).
- Muscle strains.

## How it is diagnosed

Examination, often while coughing or standing; ultrasound or CT if unclear.

## Treatment

- Hernias that cause symptoms are repaired, usually with a mesh.

## Clinical notes

- Landmark for the midline in the Pfannenstiel incision used for caesarean section and pelvic surgery

## Anatomical variants

- Absent on one or both sides; when present it may be larger on one side or, rarely, doubled

## Test yourself

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

## What are the attachments of the pyramidalis?

From the pubic crest and pubic symphysis to the linea alba, about midway between pubis and umbilicus; it lies in front of the lower rectus abdominis inside the rectus sheath.

## What is the action and nerve supply of the pyramidalis?

It tenses the linea alba; it is supplied by the subcostal nerve (T12), with some texts adding the iliohypogastric or ilioinguinal nerve (L1).

## Why is the pyramidalis useful in a Pfannenstiel incision?

The paired pyramidalis muscles mark the midline just above the pubis; they are separated to find the linea alba once the anterior rectus sheath is opened.

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

## Its names

**Official Spanish (DeCS)**
Músculo piramidal

**English (TA2)**
Pyramidalis

Sources: [Anatomy, Abdomen and Pelvis, Rectus Sheath](https://www.ncbi.nlm.nih.gov/books/NBK537153/).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/anatomy/pyramidalis/
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