Rectus sheath !

The rectus sheath is the tough fibrous casing around the rectus abdominis, the long vertical muscle at the front of the belly.

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What it is

The tough envelope around each rectus muscle, made of the tendon sheets of the three flat muscles.

What it does

Holds the rectus in place; surgeons close it carefully after a midline incision to prevent a hernia.

Key facts

Where: Aponeurotic sheath around rectus abdominis and pyramidalis, from xiphoid/costal cartilages 5–7 to pubis
Attaches: Above arcuate line: front = external + internal oblique, back = internal oblique + transversus; below it all pass in front, transversalis fascia behind
Function: Holds rectus in place; contains superior and inferior epigastric vessels and T7–T12 ventral rami; fuses medially as the linea alba

Relations

In front: Above the arcuate line: external oblique aponeurosis and the front lamina of the internal oblique aponeurosis; below it: all three flat-muscle aponeuroses; then subcutaneous tissue and skin
Behind: Above the costal margin: costal cartilages 5–7 directly (no posterior layer); down to the arcuate line: back lamina of the internal oblique plus the transversus abdominis aponeurosis; below it: transversalis fascia, extraperitoneal fat and peritoneum
Medial: The linea alba, where the sheaths of both sides interlace
Lateral: The linea semilunaris, where the aponeuroses of external oblique, internal oblique and transversus abdominis meet to split around the muscle
Contents: Rectus abdominis and pyramidalis; superior and inferior epigastric vessels; the ends of the lower intercostal nerves and the subcostal nerve, which enter from the side

How to find it

In a lean, muscular person lying on the back who lifts the head and shoulders, the lateral edge of the sheath shows as a curved groove from the tip of the ninth costal cartilage down to the pubic tubercle. The arcuate line can't be felt; at laparoscopy it is seen from inside as the curved lower edge of the posterior layer.

Examination

Carnett sign: pain that stays the same or worsens when the abdominal muscles are tensed (head raise) points to a source in the wall, such as a sheath hematoma or nerve entrapment, rather than inside the abdomen
Fothergill sign: a wall mass that stays palpable and does not cross the midline when the rectus abdominis contracts suggests a rectus sheath hematoma

On imaging

Ultrasound shows the rectus abdominis between the bright anterior and posterior layers; it guides the rectus sheath block. On CT a sheath hematoma is a spindle-shaped mass within the muscle; below the arcuate line it is often larger and can track down toward the pelvis.

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

Rectus sheath hematoma: bleeding from an epigastric artery after violent coughing, trauma or anticoagulation; a painful, tender wall mass
Rectus sheath block: local anaesthetic placed between the rectus abdominis and the posterior layer numbs the midline skin for umbilical and midline incisions; the TAP block covers the lateral wall instead
Spigelian hernia: through the aponeurosis along the linea semilunaris, usually near or below the arcuate line; it often lies under the external oblique aponeurosis, so it can be hard to feel
In a paramedian incision the anterior layer is opened and the rectus abdominis is moved aside rather than cut, which protects its segmental nerves

Anatomical variants

The arcuate line can be a sharp curved edge or a gradual thinning of the posterior layer with no clear border, and its height varies (some texts place it about a third of the way from the umbilicus to the pubis)

Test yourself

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

What changes in the rectus sheath at the arcuate line?

The posterior layer stops: below the arcuate line all three flat-muscle aponeuroses pass in front, and the rectus abdominis rests only on transversalis fascia and peritoneum.

What are the contents of the rectus sheath?

Rectus abdominis and pyramidalis, the superior and inferior epigastric vessels, and the ends of the lower intercostal (T7–T11) and subcostal nerves entering from the side.

What causes a rectus sheath hematoma and how does it present?

Bleeding from an epigastric artery after violent coughing, trauma or anticoagulation; a painful, tender wall mass, often larger below the arcuate line, where no posterior layer contains it.

Which hernia occurs along the lateral edge of the rectus sheath?

Spigelian hernia, through the linea semilunaris, usually near or below the arcuate line; it often lies under the external oblique aponeurosis, so it can be hard to feel.

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

Its names

Official Latin (TA2): vagina musculi recti abdominis TA2 2359
Official Spanish (DeCS): Vaina del músculo recto del abdomen
English (TA2): Rectus sheath

Sources: Terminologia Anatomica (TA2); Anatomy, Abdomen and Pelvis, Rectus Sheath.

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Representative model, for educational purposes only.

Rectus sheath highlighted on the Durgical 3D model