Lesser Thoracic Splanchnic Nerve

The lesser thoracic splanchnic nerve is one of the three major thoracic splanchnic nerves that carry preganglionic sympathetic fibers from the thorax into the abdominal cavity. It originates from the lower thoracic sympathetic ganglia and transmits fibers that primarily influence midgut structures by synapsing in the aorticorenal ganglion or renal plexus.

Origin

The lesser splanchnic nerve arises from the 10th and 11th thoracic sympathetic ganglia. These ganglia receive preganglionic fibers from the lateral horn of spinal cord segments T10 and T11. The nerve typically appears as a single bundle, though variations can include multiple small fascicles.

Course

From its origin in the lower thoracic sympathetic chain, the lesser thoracic splanchnic nerve descends medially and slightly inferiorly through the posterior thoracic cavity. It travels along the vertebral column and passes through the diaphragm—either via the crus or through a separate small foramen—to reach the retroperitoneum of the upper abdomen.

Termination

After passing through the diaphragm, the lesser splanchnic nerve synapses in the aorticorenal ganglion, located near the origin of the renal arteries. Some fibers may also contribute directly to the renal plexus, supplying the kidneys and upper ureter.

Contents

• Preganglionic sympathetic fibers: From spinal cord levels T10–T11
• Visceral afferent fibers: Carry sensory information from abdominal organs back to the spinal cord

Innervation Targets (via Postganglionic Fibers)

• Kidneys
• Upper part of ureters
• Small portions of adrenal glands (variable)
• Midgut derivatives (via collateral overlap with celiac or superior mesenteric plexuses)

Topographic Relationships

• Posterior: Vertebral bodies (T10–T12)
• Anterior: Diaphragmatic crura, retroperitoneal connective tissue
• Medial: Greater and least splanchnic nerves (adjacent)
• Lateral: Descending thoracic aorta and sympathetic trunk

Histological Structure

The lesser splanchnic nerve is composed of:

• Myelinated preganglionic fibers: From thoracic spinal cord
• Unmyelinated afferent fibers: Carrying visceral pain and stretch sensations
• Connective tissue sheath: Enclosing and protecting nerve bundles

Clinical Significance

• Visceral pain referral: Midgut organs innervated by these fibers may refer pain to the lower thoracic dermatomes (T10–T11), including the periumbilical region
• Splanchnic nerve block: May be used for pain relief in renal cancer or other upper abdominal malignancies

Topographic Summary

• Origin: Thoracic sympathetic ganglia T10–T11
• Course: Descends along vertebral column, passes through diaphragm
• Termination: Aorticorenal ganglion or renal plexus
• Function: Sympathetic innervation to kidneys, ureters, and midgut structures