Capsules of the Thyroid Gland
The thyroid gland is enclosed by two capsules — a true (inner) capsule and a false (outer) capsule — with important surgical and anatomical structures lying between them.
True Capsule
- A thin fibrous layer derived from and firmly adherent to the gland itself
- Sends fibrous septa (trabeculae) into the substance of the gland, dividing it into lobules
- Each lobule contains 20–40 follicles
- The true capsule is continuous with the fibrous stroma of the gland
False Capsule (Surgical/Pretracheal Fascia Sheath)
- Derived from the pretracheal (middle) layer of deep cervical fascia
- Forms a loose sheath around the gland
- Sends thickenings (condensations) to anchor the gland:
- Posteriorly: suspensory ligament of Berry (ligament of Berry) — attaches the posteromedial aspect of each lateral lobe to the cricoid cartilage and first two tracheal rings
- Anteriorly: reflected forward over the isthmus
Space Between the Two Capsules
The loose areolar tissue between the true and false capsule contains:
- Parathyroid glands (usually 4 in number — 2 superior, 2 inferior)
- Terminal branches of the thyroid arteries
- Tributaries of the thyroid veins
- Anastomosing vessels
This space is the surgical plane developed during thyroidectomy to separate the gland from its sheath while preserving the parathyroid glands and recurrent laryngeal nerves.
Clinical Importance of the Ligament of Berry
- The ligament of Berry anchors the posteromedial aspect of the thyroid gland to the cricoid and trachea
- The recurrent laryngeal nerve passes in close relation to this ligament — posterior or just lateral to it — before entering the larynx
- During thyroidectomy, ligation near the ligament of Berry risks injury to the recurrent laryngeal nerve → hoarseness, respiratory distress
Why the Gland Moves on Swallowing
The false capsule is derived from pretracheal fascia, which is attached superiorly to the thyroid and cricoid cartilages and the hyoid bone. These structures ascend during deglutition, carrying the thyroid gland upward.
This explains why any thyroid swelling (goitre) moves upward on swallowing — a key clinical sign to distinguish thyroid pathology from other neck swellings.