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 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
Relations
- In front
- Anterior layer of the rectus sheath (all three flat-muscle aponeuroses at this level), subcutaneous fat and skin
- Behind
- Lower part of the rectus abdominis
- Medial
- The pyramidalis of the other side, the two meeting at the linea alba
- Below
- Its base on the pubic crest and the front of the 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.
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.
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Representative model, for educational purposes only.
