Third head of gastrocnemius

Accessory
split of lateral head of gastrocnemius muscle. Coronal image at the level of popliteal fossa. Note the fusiform shape of the accessory split (arrowhead) of the lateral gastrocnemius (LG).
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Accessory
split of lateral head of gastrocnemius muscle. Midsagittal level. Note the small attachment of the split (arrowhead) to the posterior femoral cortex. LG=lateral head of gastrocnemius.
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Accessory
split of lateral head of gastrocnemius muscle. Sequential axial slices. Note the split (arrowheads) located between the lateral head of gastrocnemius muscle (LG) and the vessels of the popliteal fossa. It is fused caudally with the lateral gastrocnemius.
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Accessory
split of lateral head of gastrocnemius muscle. Type I (5.6%). Red area=popliteal artery, blue area=popliteal vein, brown area=gastrocnemius muscle.
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Accessory
split of lateral head of gastrocnemius muscle. Type II (13.6%). Red area=popliteal artery, blue area=popliteal vein, brown area=gastrocnemius muscle.
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Accessory
split of lateral head of gastrocnemius muscle. Type III (37,5%). Red area=popliteal artery, blue area=popliteal vein, brown area=gastrocnemius muscle.
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Accessory
split of lateral head of gastrocnemius muscle. Type IV (9%). Red area=popliteal artery, blue area=popliteal vein, brown area=gastrocnemius muscle, grey area=popliteus muscle, small grey area=fibrous band.
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Accessory
split of lateral head of gastrocnemius muscle. lateral accessory gastrocnemius split (9%). Red area=popliteal artery, blue area=popliteal vein, brown area=gastrocnemius muscle, grey area=popliteus muscle, small grey area=fibrous band.
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Radiopaedia • CC-by-nc-sa 3.0 • de

Third head of gastrocnemius, also known as accessory head of gastrocnemius, is a normal anatomical variation where there is an accessory muscle bundle of the gastrocnemius muscle in addition to the medial and lateral heads.

Epidemiology

It is the most common variation of the gastrocnemius. Its occurrence was estimated to be between 2.0% and 5.5% of the normal population .

Clinical picture

Most of the cases are asymptomatic. It can cause compression upon popliteal vessels resulting in clinical symptoms such as popliteal artery entrapment syndrome resulting in claudication in young patients and popliteal vein entrapment . Rarely, it can cause sural nerve entrapment .

Radiographic features

It is usually seen in cross-sectional imaging modalities and best identified with MRI. It arises near midline of posterior distal femur and joins the medial or lateral head of gastrocnemius muscle, coursing lateral to the popliteal vessels. The size varied from a thin threadlike muscle to a rather bulky muscle.

History and etymology

It was first described in 1813 by Kelch and was further detailed by Frey in 1919 .

Siehe auch:
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Assoziationen und Differentialdiagnosen zu Aufsplittung lateraler Kopf des Musculus gastrocnemius:
Musculus
gastrocnemius
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