SG

Chapter Notes on Neonatal and Pediatric Kidneys and Adrenal Glands

Chapter 27: The Neonatal and Pediatric Kidneys and Adrenal Glands

Objectives

On completion of this chapter, you should be able to:

  • Discuss the development of the ovaries and the male genital tract.

  • Describe the normal sonographic appearance of the pediatric female pelvis and pediatric scrotum.

  • Describe when external genitalia may be seen by ultrasound.

  • Detail the sonographic findings and appearance of congenital anomalies and pathological conditions discussed in this chapter.

  • Describe the difference between true precocious puberty and precocious pseudopuberty.

  • Describe the complications and differential considerations for ovarian cysts.

Adrenal Hemorrhage

Causes

  • Difficult delivery

  • Large size

  • Infants of diabetic mothers

  • Stress and hypoxia at delivery

  • Septicemia

  • Shock
    These factors predispose the neonate to the development of adrenal hemorrhage.

Clinical Presentation

The newborn with adrenal hemorrhage may present with:

  • Abdominal mass

  • Jaundice

  • Anemia
    Even without these associated complications.

Sonographic Findings

  • Ovoid enlargement of the gland or a portion of the gland.

  • Appearance can range from anechoic to hyperechoic or a mixture of echogenicities, depending on the extent and age of the hemorrhage.

  • Significant enlargement blunts the superior pole of the underlying kidney and causes its inferior displacement.

  • The initial appearance may be indistinguishable from adrenal neuroblastoma. Follow-up sonography can differentiate these entities. The hemorrhagic adrenal gland typically decreases in size within 4 to 6 weeks, and calcification may be noted on follow-up imaging.

Differential Diagnosis

  • Neuroblastoma: Poorly defined, heterogeneous with irregular hyperechoic areas due to calcifications.

  • Wilms’ Tumor: Well-encapsulated, somewhat homogeneous and heterogeneous.

  • Intraspinal extension in neuroblastoma can occur in 15% of patients, prompting evaluation of the spinal canal using ultrasonography.

Embryology of the Female Genital Tract

Development of the Gonads

  • Gonads arise from parts of the urogenital ridges known as gonadal ridges.

  • The gonadal ridges enlarge and develop a mesentery (mesovarium) that separates from the mesonephros.

  • Coelomic epithelium over the gonadal ridges forms primary sex cords that grow into the mesenchyme.

  • Primordial germ cells enter the primary sex cords to give rise to ova.

Development of the Ovaries

  • In XX female embryos, gonads differentiate later than in male embryos.

  • Primary sex cords converge to form rete ovarii, which subsequently disappear.

  • Surface epithelium gives rise to secondary sex cords (cortical cords) which incorporate primordial germ cells.

  • By 16 weeks gestation, cortical cords break into primordial follicles, each containing an oogonium surrounded by a layer of flattened follicular cells.

  • Oogonia multiply rapidly via mitosis and enlarge to form primary oocytes before birth, entering the first meiotic prophase but remaining arrested until puberty.

Development of the Genital Ducts

  • All embryos initially possess both genital duct pairs.

  • Female (paramesonephric) ducts develop into the female reproductive system, while a male genital duct system is present but dormant until differentiation occurs at around the 9th week of gestation.

Development of the External Genitalia

  • External genitalia appear similar in both sexes until the 9th week of gestation.

  • By the 12th week, external organs are fully developed, with the urethra and vagina opening into the urogenital sinus, which becomes the vestibule of the vagina.

  • Urogenital folds develop into labia minora, labioscrotal swellings into labia majora, and the phallus into the clitoris.

Normal Sonographic Appearance of the Pediatric Female Pelvis

  • High-resolution sonography allows evaluation of the neonatal and pediatric pelvic cavity, often utilizing a distended bladder to visualize the pelvic anatomy.

  • If distension is inadequate, catheterization and saline instillation may be required. Hydrosonovaginography can also outline the vagina in cases of pelvic masses or congenital abnormalities.

Bladder

  • Normal bladder should have a smooth, thin wall; thickness < 3 mm when distended, average around 1.5 mm. If empty, thickness may increase but not exceed 5 mm.

  • Distal ureters may not be routinely visualized unless dilated; color Doppler can aid in imaging ureters as they enter the bladder.

  • Postvoid scans can provide information about bladder emptying capacity.

Uterus

  • In newborns, the uterus is prominent and thickened with a bright echogenic endometrial lining due to maternal hormonal stimulation. The pear-shaped uterus has a length of approximately 3.5 cm with a fundus-to-cervix ratio of 1:2.

  • At ages 2-3 months, the uterus regresses to prepubertal size (2.5-3 cm long, 1:1 ratio). It grows significantly during puberty, reaching lengths of 5-7 cm and a 3:1 fundus-to-cervix ratio.

Vagina

  • Best visualized longitudinally with a distended bladder, appearing as a tubular structure posterior to the bladder, continuous with the uterine cervix.

Ovary

  • Neonatal ovaries may be located between the lower poles of the kidneys and the true pelvis. Normal ovarian volume varies, determined by the prolate-ellipse formula: Volume = Length imes Height imes Width imes 0.523. Mean volumes for premenarchal ages are reported.

  • Neonatal ovaries are typically heterogeneous due to tiny cysts, larger cysts being more common post first year of life.

Pathology of the Pediatric Genital System

Congenital Anomalies of the Uterus and Vagina

  • Müllerian anomalies occur when the normal development of the uterus and vagina is disrupted, comprising approximately 0.5% of females and associated with obstetric complications.

Sonographic Findings

  • Examination of the uterus is crucial when anomalies are suspected; visualization may reveal abnormal uterine configurations on sonograms.

Classifications of Müllerian Anomalies

  1. Class I: Segmental agenesis, resulting in vaginal atresia leading to fluid accumulation (hydrocolpos, hydrometrocolpos).

  2. Class II: Unicornuate uterus, identified by deviation and often associated with contralateral renal agenesis.

  3. Classes III - V: Include Uterus didelphys, Bicornuate uterus, and Septate uterus, characterized by duplication of uterine cavities, often presenting subtle sonographic differences.

  4. Class VI: Effects related to diethylstilbestrol exposure, leading to a T-shaped uterine cavity.

Ambiguous Genitalia

  • Errors in sexual development can result in ambiguous genitalia, with diagnostic sonography assisting in the identification of gonads and internal structures.

Precocious Puberty

Types of Precocious Puberty

  • True Precocious Puberty: Isosexual development with increase in gonad size and secondary sexual characteristics.

  • Precocious Pseudopuberty: Involves secondary characteristics without gonadal activation, often due to external hormone exposure.

Common Neonatal Pathologic Conditions

Clinical Findings

  • Ovarian Torsion: Severe abdominal pain with high risk of necrosis if unrecognized.

  • Ovarian Teratomas: Asymptomatic mass, potential for abdominal distention, may mimic appendicitis symptoms.

Sonographic Findings

  • Typical findings include enlarged ovaries, fluid in the cul-de-sac, and specific features depending on the condition.

Differential Diagnosis Considerations

Differential considerations involve various cysts, infections, appendicitis, and other gastrointestinal conditions.