Section 6.3: Small Parts & Superficial Pathology

Small Parts and Superficial Pathology

Small parts sonography encompasses the thyroid gland, scrotum, prostate, and superficial structures like the abdominal wall. High-frequency, high-resolution transducers are essential to visualize superficial details and assess vascular flow.

Thyroid and Parathyroid Pathology

Thyroid pathology is broadly categorized into diffuse diseases and nodular lesions.

• Goiter: Goiter represents a diffuse enlargement of the thyroid gland, which can be simple (smooth, homogeneous) or multinodular (heterogeneous, containing multiple nodules).
• Follicular Adenoma: This is the most common benign thyroid nodule. Typically, it appears as a solitary, well-defined, round-to-oval mass that is hypoechoic, isoechoic, or hyperechoic relative to normal thyroid tissue. A key sonographic feature is the presence of a complete hypoechoic halo surrounding the nodule, which represents compressed parenchymal tissue or a fibrous capsule.
• Thyroid Carcinoma: Papillary carcinoma is the most common thyroid malignancy. Sonographic markers associated with high risk of malignancy include hypoechogenicity, irregular or microlobulated margins, a "taller-than-wide" shape (anteroposterior diameter greater than transverse diameter), and the presence of microcalcifications (psammoma bodies). Microcalcifications appear as punctate, highly echogenic foci without posterior acoustic shadowing. Central or intranodular vascularity is also suspicious.
• Parathyroid Adenoma: Normal parathyroid glands are located posterior to the thyroid lobes and are generally not resolved on ultrasound due to their small size (<4 mm). A parathyroid adenoma is a benign, hyperfunctioning tumor of the parathyroid gland, which presents clinically as primary hyperparathyroidism, elevated serum calcium, and elevated parathyroid hormone (PTH). Sonographically, it appears as a solitary, well-demarcated, oval, hypoechoic solid mass located posterior to the thyroid. It classically exhibits a feeding polar vessel on color Doppler.

Scrotal and Testicular Pathology

Scrotal sonography is the primary method for evaluating acute scrotal pain and intratesticular masses.

• Testicular Torsion: Torsion is a surgical emergency caused by twisting of the spermatic cord, obstructing venous drainage and arterial supply. Intravaginal torsion is the most common form, often secondary to the "bell-clapper" deformity (abnormal high attachment of the tunica vaginalis). Clinically, it presents as sudden, severe unilateral scrotal pain. In the acute phase (<6 hours), the testis may appear sonographically normal, enlarged, or slightly hypoechoic. The definitive diagnostic finding is the complete absence of blood flow within the affected testis on color and spectral Doppler, whereas flow is normal or hyperemic in the contralateral testis. Chronically (>24 hours), the testis becomes heterogeneous and necrotic.
• Epididymitis and Orchitis: Epididymitis is the most common cause of acute scrotal pain in post-pubertal males, typically resulting from bacterial infection. Sonographically, the epididymis (commonly the head) appears enlarged and hypoechoic with a reactive hydrocele and thickened scrotal wall. The hallmark feature is diffuse hypervascularity (hyperemia) on color Doppler. If the infection spreads to the testis (epididymo-orchitis), the testis will appear enlarged and hypoechoic with marked hypervascularity.
• Testicular Neoplasms: Intratesticular masses are highly likely to be malignant, whereas extratesticular masses are usually benign.
  • Seminoma: The most common germ cell tumor, presenting as a solitary, well-defined, homogeneous, hypoechoic intratesticular mass. It rarely contains calcifications or cystic spaces.
  • Non-Seminoma (e.g., embryonal cell carcinoma, teratocarcinoma, choriocarcinoma): These tumors are more aggressive, heterogeneous, and poorly marginated, often containing cystic components, hemorrhage, and echogenic calcifications.

Prostate Pathology

The prostate gland is divided into three main glandular zones: the peripheral, transition, and central zones.

• Benign Prostatic Hyperplasia (BPH): BPH is a benign enlargement of the prostate, primarily occurring in the transition zone, which surrounds the urethra. It is extremely common in aging men and presents with urinary obstruction (nocturia, hesitancy). Sonographically, BPH causes enlargement of the gland (>30 cc volume), which appears heterogeneous, often with calcifications and cystic changes in the transition zone.
• Prostate Cancer (Adenocarcinoma): The majority of prostate cancers (70% to 80%) arise in the peripheral zone, which is located posteriorly and is easily palpated during a digital rectal exam (DRE). On ultrasound (especially transrectal ultrasound or TRUS), prostate cancer classically appears as a hypoechoic, subcapsular nodule in the peripheral zone. It often demonstrates increased vascularity on color Doppler.

Abdominal Wall Hernias

An abdominal wall hernia is a protrusion of abdominal contents (omentum, peritoneal fat, or bowel loops) through a defect in the abdominal wall musculature.

• Epigastric Hernia: Occurs in the midline of the linea alba, between the xiphoid process and the umbilicus.
• Umbilical Hernia: Protrusion through the umbilical ring.
• Spigelian Hernia: A rare hernia occurring along the Spigelian fascia (aponeurosis of the transversus abdominis muscle, lateral to the rectus abdominis muscle) at the level of the arcuate line.
• Incisional Hernia: Protrusion through a previous surgical scar.
• Scanning Technique: The sonographic evaluation of hernias must be dynamic. Real-time scanning should be performed while the patient is at rest and during the Valsalva maneuver (straining). The Valsalva maneuver increases intra-abdominal pressure, which helps to push the herniated contents through the defect, revealing the hernia sac and contents. The neck of the hernia defect must be measured, and the sonographer must assess the mobility and compressibility of the contents. If bowel is present, peristalsis should be checked. An incarcerated hernia cannot be pushed back into the abdomen, and a strangulated hernia exhibits compromised blood supply (absent color Doppler flow in the herniated tissue), which requires emergency surgery.

Summary of Small Parts & Superficial Pathology