Shape | Thyroid

Jessica Humphries Genoveva Pederique MD Ashley Davidoff MD

The Common Vein

Introduction

The thyroid is a butterfly-shaped gland with two lobes each an inverted cone. Together their shape varies from an H to a U shape in the coronal plane. It is also U-shaped or horseshoe shaped in the axial projection.

The thyroid gland gets its name from the Greek word for shield given its shape and the shape of the thyroid cartilage on which it rests. In some patients a pyramidal lobe extends cranially from the isthmus representing residual thyroglossal duct tissue that assumes thyroid character.

The shape of the thyroid cannot be observed through clinical examination; however, the “thyroid neck check,” which requires a patient to observe his/her neck for asymmetrical bulges while swallowing, may reveal irregularities in its shape.

The Butterfly Shaped Organ

The butterfly shaped form of the thyroid gland is appreciated in this image.

“H” or “V”or ‘U” shaped Gland

The H V or U shaped form of the thyroid gland is appreciated in this image. The isthmus may be broad in its craniocaudad dimension or may be relatively narrow. In the anteroposterior dimension it is only about 3-5mm thick

Variation in the Normal Shape of the Thyroid

The shape of the thyroid is well appreciated with the two lobes connected by the isthmus. The size and shapes of the two lobes may vary.

Courtesy Ashley Davidoff MD 93852.8kb15.3kb09b01.8s

The Pyramidal Lobe

A variation in this shape of the thyroid gland is created by the presence of a pyramidal lobe which is an embryological remnant of the thyroglossal duct. It is characterized by a third small cone that lies between the lobes and sometimes originates off one of the lobes more commonly the left.

In the Transverse or Axial Projection

Thyroid Gland in Axial Projection – CT scan

The axial CTscan of the neck shows the thyroid gland with the right and left lobes (pink) The gland is horseshoe shaped, and while on the horse theme the gland in this projection could also be viewed as a saddle with saddle bags n either side. The thyroid surrounds the similarly shaped trachea (black). Note in this case the right lobe is slightly larger than the left.

Axial Image – Ultrasound Scan

The transverse ultrasound of the thyroid gland shows the asymmetric symmetry of the lobes. In this cut the right lobe is slightly larger than the left and the isthmus consists of a narrow band that is only about 5mms thick.

Multinodular Thyroid

The Distinction between Normal Displaced Thyroid Tissues and Nodule is Sometimes Difficult to Discern

The 75 year old male presents with an asymptomatic multinodular goiter, consisting many nodules of varying size and density, some with macrocalcifications as seen by coronal CT reconstruction (a,b) and axial images (c,d). The windows of the CTscan have been narrowed (a,c), to enhance the morphological characteristics of the components of retrosternal goiter. Each lobe of the thyroid measures about 12 cms in sagittal 6cms. in transverse and 12cms in A-P dimension. These findings are consistent with a non toxic multinodular goiter.

Types of Goiter That Change the Shape of the Gland

The diagram illustrates non toxic multinodular goiter together with a normal thyroid gland on the left. A moderately enlarged gland (middle) containing multiple variably sized non toxic nodules with different characteristics is shown together with a massively enlarged non toxic gland (right) When the gland becomes massively enlarged it may extend into the chest, compress the airway and neck veins as well as displace other structures such as the esophagus.