Arthur C. Fleischer and Charles S. Odwin*
The thyroid is an endocrine gland that secretes three major hormones: thyroxine (T4), triiodothyronine (T3), and calcitonin. The thyroid is located in the neck and has two lobes connected anteriorly by a narrow band of tissue, referred to as the isthmus.
The common carotid artery and internal jugular vein lie posterior and lateral, defining the posterolateral margins of the thyroid. The “strap muscles” lie anterior to the lateral aspect of the thyroid defining the anterolateral margins of the thyroid.
Surrounding Musculature and Structures
Sternohyoid muscle—anterior and slightly lateral
Sternothyroid muscle—posterior to the sternohyoid
Longus colli muscle—adjacent to the trachea and is posterior to the thyroid and the common carotid arteries
Esophagus—slightly to the left of midline and posterior to the thyroid
Sonographically, the thyroid has a homogeneous echogenicity that is greater than the strap muscles.
Normal Measurements of the Thyroid
Physiologically, there are two basic conditions that occur with the thyroid: hypothyroidism or hyperthyroidism. The anterior pituitary gland produces a thyroid-stimulating hormone (TSH), which regulates the hormones secreted by the thyroid gland. Table 5–1 outlines the pathologies of the thyroid that can be imaged sonographically.
TABLE 5–1 Thyroid Pathology
SONOGRAPHY OF THYROID NODULES
Sonography provides important clinical information regarding the presence of a thyroid nodule, its internal consistency, and number of lesions. High-frequency transducers provide detailed depiction of the relative size, location, border, and vascularity with color Doppler sonography. There are certain parameters that the sonographer should document such as
• Internal consistency
• Cervical lymphadenopathy
Sonographers should also be aware of certain “classic patterns” that allow characterization of thyroid nodules. These patterns can be divided with those that require fine needle aspiration (FNA) biopsy and those that usually do not need FNA. Findings usually requiring FNA include
• Nodules containing microcalcifications—These are usually papillary cancers.
• Hyperechoic solid nodules with coarse calcification or echogenic foci—These can also be seen in medullary and papillary cancers or rarely in benign lesions. These nodules should undergo FNA.
• Solid nodule with peripheral calcifications—These are usually benign follicular adenomas but may need resection for histologic evaluation.
• Nodules with edge shadowing—This may arise from a fibrous capsule of a thyroid cancer.
Findings that usually do not require FNA include:
• Nodules containing echogenic foci with “ring-down” artifact—These usually correspond to condensed colloid within a benign nodule.
• Nodules containing “honeycomb” pattern—These are typical of a benign colloid adenoma.
• Cystic nodules are typically benign.
• Multiple hypoechoic foci—These are typical of chronic lymphocytic (Hashimoto’s) thyroiditis.
The sonographer should also document the size, shape, and morphology of cervical lymph nodes. Abnormal findings include enlargement (>6 mm height), hypoechoic areas, and microcalcification. Papillary thyroid cancers can be associated with spread to lymph nodes. “Reactive” lymph nodes can also be seen with neck inflammation.
Sonographers may also assist in guided FNA of one or more abnormal thyroid masses.
The interested reader is referred to the article below for further discussion of the various sonographic features of thyroid nodules.1
The scrotum is a sac that is continuous with the abdomen and is divided by a septum, the medial raphe. Each space contains a testis, and epididymis, a portion of spermatic cord, and the ductus deferens (Fig. 5–1). A thin, double layer of peritoneum and the tunica vaginalis line the inner wall of the scrotum. This double layer of peritoneum normally contains a small amount of fluid.
FIGURE 5–1. A and B. Section anatomy of the testis and epididymis.
The testicles are ovoid glands that measure approximately 4 × 2 × 3 cm. A dense white fibrous capsule, tunica albuginea, encases each testicle and then enters the gland, separating the testes into approximately 200 cone-shaped lobules. Within these lobules, two primary functions occur: spermatogenesis (the production of spermatozoa) and the secretion of testosterone by the interstitial cells (Leydig cells).
The secretions are carried through the lobules to the rete testis. A series of ducts, efferent ductules, drain the rete testis, piercing the tunica albuginea and entering the head of the epididymis.
The epididymis consists of a single tightly coiled duct that drapes the posterior aspect of the testis. The most superior aspect of the epididymis is the head, followed by the body and tail. This duct continues as the ductus deferens (vas deferens), leaving the pelvis via the inguinal canal with the testicular artery, the draining veins of the scrotum, nerves, and lymphatics to form the spermatic cord. Each spermatic cord now extends over the top and down the posterior surface of the bladder, coming together to join the duct from the seminal vesicle to form the ejaculatory ducts. The ejaculatory ducts pass through the prostate gland to terminate in the urethra.
Normal Sonographic Anatomy of the Scrotum
The normal testicle has a homogeneous echo pattern of medium-level echogenicity The skin is a thin, smooth, echogenic, linear structure measuring <2 mm. Posteriorly and superiorly capping the testis, the epididymal head is clearly distinguished because of its coarser, more echogenic pattern. The body of the epididymis is more difficult to differentiate because of its posterior position, and the tail is rarely seen. A bright echogenic band, representing the mediastinum testis, is seen in the 9 o’clock position; on the left side, it is seen in the 3 o’clock position. Between the layers of the tunica vaginalis, a small amount of fluid is normally found.
The testicular artery and veins of the pampiniform plexus, which run along the posterior aspect of the testicle in the region of the epididymis, are not normally seen.
Scanning the testis transversely, comparing each testis and epididymis as to size, echogenicity, and vascularity, is the best guide for detecting lesions, enlargement, or torsion.
There are no specific laboratory tests that are used to identify scrotal pathology. A decrease in sperm count may occur in cases of male infertility. (Table 5–2 outlines scrotal pathology associated with clinical and sonographic findings.)
TABLE 5–2 • Scrotal Pathology