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Imaging anatomy and radiographic projections of sciatic nerve
Presenter Dr.Daniel B.RRI
Moderator Dr. Haileslassie T. Radiologist

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Outlines
• Introduction
• Anatomy and course of sciatic nerve
• Imaging
• Variants

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Introduction
• Nerve is basic unit of peripheral nervous system.
• With in a nerve each axon is surrounded by layer of
connective tissue called endoneurium
• Axons are bundled together in to groups called fascicles.
• Each fascicle is surrounded by connective tissue called
perineurium.

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• The entire nerve is covered by a connective tissue layer called
epineurium.
• Perineurium is a layer of fatty cells.
• The endoneurium contains low protein liquid called
endoneurial fluid.

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Nerves of lower extremity
Sciatic nerve
• Arises from L4, L5, S1, S2, S3, branches of sacral plexus.
• It’s the longest and widest nerve in the body.
• Two nerves (common peroneal and tibial) bound together.
• Exits pelvis through the greater sciatic foramen inferior to
piriformis muscle.

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• Crosses over superior gemellus, obturator internus, inferior
gemellus muscles.
• It is deep to long head of biceps femoris muscle.
• Branches arising in thigh:
- Articular to hip,
- Nerves to hamstring muscles

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 Common Peroneal Nerve
• Also known as common fibular nerve and forms lateral part of
sciatic nerve.
• Smaller of 2 terminal divisions of sciatic nerve.
• Arises from dorsal divisions of sacral plexus (L4-S2)
• Separates from tibial nerve at superior angle of popliteal fossa.

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• Leaves popliteal fossa by crossing plantaris and lateral head of
gastrocnemius.
• Oblique lateral course with biceps femoris muscle.
• Innervates short head of biceps femoris muscle.
• Ends between lateral side of neck of fibula and peroneus
longus.

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• Divides into its two terminal branches in the peroneus longus
muscle.
1.superficial peroneal nerve
2.deep peroneal nerve
 Other branches are:
-Peroneal communicating nerve
-Lateral sural cutaneous nerve
-Superior and inferior genicular nerves
-Recurrent genicular nerves
-Muscular branches

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 Motor supply:
• short head of biceps femoris.
• muscles of the extensor compartment of the leg by deep peroneal nerve.
• Muscles of the lateral compartment of the leg by superficial peroneal nerve
 Sensory supply: cutaneous innervation of posterolateral leg.
 Fibular neck fracture may result in foot drop.

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Tibial Nerve
• Largest division of sciatic nerve.
• Arises from ventral surface of sacral plexus(L4-S3) and runs
medially.
• Courses through the popliteal fossa passing deep to
gastrocnemius muscle.

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• It passes inferiorly between the heads of gastrocnemius and
deep to soleus muscle.
• Continues inferiorly in the midline deep to soleus and
superficial to the tibialis posterior muscle.
• At the ankle passes under flexor retinaculum in the tarsal
tunnel.

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• At the level of medial malleolus it divides into three terminal
branches.
1.medial plantar nerve
2.lateral plantar nerve
3.medial calcaneal nerve

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• Motor supply:
- posterior thigh muscles except short head of biceps femoris
muscle.
- Posterior compartment of the leg
- Muscles of the sole of the foot
 Sensory supply:
-Articular branches to knee, ankle and foot joints
-Cutaneous branches to posterior calf and sole of the foot

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Sural Nerve
• Sensory nerve of the lower limb.
• Its formed by the union of sural branch of tibial nerve and
communicating sural branch of common fibular nerve.
• Travels within subcutaneous tissue adjacent to small saphenous vein.
• It descends behind the lateral malleolus and becomes lateral dorsal
cutaneous nerve.

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 It contains nerve roots of S1 and S2 and provides sensation to:
Lower lateral calf
Lateral ankle
Lateral foot and some of the 5th
digit
 Sural communicating branch of common peroneal nerve is
absent in 20% of the population.
 Injury to this nerve is well tolerated and its often used for nerve
grafting or biopsy.

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 Femoral Nerve
• Arises from posterior divisions of L2-L4 roots of the lumbar plexus.
• Largest branch of lumbar plexus.
• It emerges from the lateral boarder of the psoas muscle and medial boarder of
iliacus muscle.
• It sends motor branch to iliacus before passing under the inguinal ligament to
enter femoral triangle.
• Exits pelvis beneath inguinal ligament, lateral to femoral vessels, enters femoral
triangle.

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Femoral triangle
• Anatomical space in the anterior upper thigh that contains
several structures.
 The boundaries are:
• Laterally medial border of Sartorius
• Medially medial border of adductor longus
• Superiorly inguinal ligament
• Floor ilopsoas laterally and pectineus medially
• Roof skin and subcutaneous tissue

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Motor supply
-Anterior compartment of the thigh
Sensory supply
-Hip
-Anterior and medial thigh
-Knee and medial leg as saphenous nerve
 The femoral nerve is responsible for patellar tendon reflex (tests L3-
L4spinal component).

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Proximal branches
Branches to iliacus before crossing inguinal ligament
Nerve to pectineus after crossing inguinal ligament
 Branches of superficial division
Nerve to Sartorius
Anterior femoral cutaneous nerve
Sympathetic vasomotor supply to blood vessels
 Deep division
Nerve to anterior compartment of thigh muscles
Saphenous nerve which passes behind Sartorius

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• Saphenous Nerve
• It’s the continuation of deep division of the femoral nerve in the
femoral triangle.
•
• Longest branch of femoral nerve, arising 2 cm below inguinal
ligament and descending via adductor canal.
• Passes posterior to Sartorius, descends posteromedial to knee where
it pierces deep fascia.
• In leg accompanies great saphenous vein.

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Imaging
• On plain radiographs nerves are characterized
by non specific soft tissue density.
• On CT scan nerves are characterized by soft
tissue density structures.

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 Ultrasound
 Use high-frequency transducers to assess nerves.
 Short axis: A typical “honeycomb” appearance with hypoechoic
fascicles and surrounding echogenic perineurium
 Long axis: Parallel hypoechoic tracts of uniform caliber.
 Distortion of this uniform appearance suggests pathology

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• Trace medium-sized nerves by following their course as they
branch from their parent.
• Small (1-2 mm) nerves are difficult to identify and location
may only be inferred by adjacent vessels.

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MRI
 T1 or PD help distinguish fluid in vessels from
nerves.
 Correlate with fluid-sensitive sequences.
 Fat fascicles are especially prominent in
sciatic nerve.

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• The abundant fat around the fascicles and the nerve itself
makes these structures clearly visible on T1-weighted images.
• Normal fascicular shape was defined as clustered similar-sized
rounded structures on T1 MR images.

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• The normal nerve shows a fascicular appearance.
• It has signal intensity from isointense to minimally
hyperintense with respect of the adjacent muscle.
• The perineural fat tissue has a homogeneous signal and a
separation plane with the adjacent structures.

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y

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Variants
• Common peroneal nerve piercing the piriformis muscle and tibial nerve
exiting below
• Common peroneal nerve travelling above piriformis and tibial nerve below
• Common peroneal nerve travelling above piriformis and tibial piercing the
piriformis muscle
• Both tibial nerve and common peroneal nerve travel below piriformis
muscle.

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Accessory piriformis muscle: rare variant
• Accessory muscle slips covering sacral foramina/sacral
nerves
• Two distinct muscle bellies fusing to form a common
tendon
• Accessory slips arising from the sacro tuberous ligament

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• Three muscle bellies
• Accessory slip arising from the main muscle
belly with separate tendinous insertion in to
greater trochanter.
• Piriformis syndrome

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Accessory femoral nerve: fibers arise separately in
lumbar plexus passes anterior to femoral nerve may
terminate as saphenous nerve.
• Saphenous nerve may terminate at knee with distribution
replaced by branch of tibial nerve.
• Femoral nerve splits into two or three separate slips with in
psoas muscle but united to descend as single bundle.

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References
• Applied Radiological Anatomy Second Edition
• FRANK H.. NETTER ATLAS OF HUMANANATOMY
• Diagnostic Ultrasound Musculoskeletal
• FUNDAMENTALS OF MUSCULOSKELETAL ULTRASOUND
• IMAGING ANATOMY MUSCULOSKELETAL SECOND EDITION
• Radiopedia.

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THANK YOU