Neonatal and Pediatric Kidneys, Adrenal Glands, and Pelvis

Chapter 27: The Neonatal and Pediatric Kidneys and Adrenal Glands & Chapter 28: The Neonatal and Pediatric Pelvis (Combined Notes)

Adrenal Hemorrhage

Clinical Presentation

• History: Often seen in a 2-week-old male with a history of neonatal mass or a 3-week-old jaundiced female.

• Predisposing Factors: Difficult delivery, large infant size, infants of diabetic mothers, stress and hypoxia during delivery, septicemia, and shock.

• Symptoms: Neonates may present with an abdominal mass, jaundice, and anemia even without the predisposing factors.

• Complications: Uncontrolled bleeding, intestinal obstruction, hypertension, adrenal abscess, or impaired renal function.

Sonographic Findings

• Appearance: Results in ovoid enlargement of the adrenal gland or a portion of it. The internal echogenicity is highly variable depending on the extent, age, and severity of the hemorrhage, ranging from anechoic to hyperechoic, or a mixture of echogenicities (Figure 27-17).

• Organ Displacement: Significant enlargement produces characteristic blunting of the superior pole of the underlying kidney and inferior displacement of the kidney.

• Differentiation from Neuroblastoma: Initially, adrenal hemorrhage can be indistinguishable from adrenal neuroblastoma. However, follow-up sonography can differentiate them:

  • Adrenal hemorrhage: The gland does not enlarge but decreases in size. Generally, within 4 to 6 weeks, the lesion becomes appreciably smaller, and subsequent calcification may be identified sonographically or radiographically.

  • Neuroblastoma: Characterized by increased vascularity within the neoplastic growth.

Adrenal Neuroblastoma

Characteristics and Spread

• Vascularity: Exhibits increased vascularity, which can be detected with Doppler evaluation, helping to differentiate it from adrenal hemorrhage.

• Metastases: Spreads early and widely, with the majority of patients presenting with metastases. Careful evaluation of the liver is crucial for metastatic disease.

• Location of Spread: The tumor spreads around the aorta, celiac, and superior mesenteric arteries. This spread pattern helps distinguish it from a Wilms' tumor.

Differentiation from Wilms' Tumor

• Wilms' Tumor: Typically well-encapsulated and somewhat homogeneous or heterogeneous.

• Neuroblastoma: Poorly defined and heterogeneous with irregular hyperechoic calcifications and kidney areas.

Intraspinal Extension

• Reported to occur in as many as 15\% of patients.

• Ultrasonography can successfully define the spinal canal in young infants, so such an examination should be considered in the initial assessment of infants with suspected neuroblastoma (Figure 27-18).

Objectives for Chapter 28: The Neonatal and Pediatric Pelvis

Upon completion, one 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 pathologic conditions discussed.

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

• Describe the complications and differential considerations for ovarian cysts.

Sonography of the Pediatric Pelvis

• Imaging Modality: High-resolution sonography is well-documented for evaluating both male and female pediatric pelves.

• Acoustic Window: A distended urinary bladder acts as an acoustic window to image pelvic anatomy. If needed, the bladder may be catheterized and filled with sterile water.

• Hydrosonovaginography: Sterile water can be used as a contrast agent to outline the vagina in pediatric patients with pelvic masses or complex genitourinary abnormalities.

• Associated Anomalies: Uterine anomalies are frequently associated with urinary tract abnormalities.

• Transducer Selection:

  • Multiple sonographic images are obtained in transverse and sagittal planes.

  • Transducers: 5 to 7.5\ MHz phased array or curvilinear broad bandwidth or sector transducer.

  • Neonatal imaging: Higher resolution transducer (7.5 to 12\ MHz).

Embryology of the Female Genital Tract

Development of the Gonads

• Origin: The gonads are the first parts of the genital system to develop, arising from the gonadal ridges (parts of the urogenital ridges).

• Process: The gonadal ridge enlarges and detaches from the mesonephros by developing a mesentery that forms the mesovarium (Figure 28-1).

• Sex Cords: The coelomic epithelium covering the gonadal ridges grows, forming primary sex cords that penetrate the mesenchyme of the developing gonads.

• Germ Cells: Primordial germ cells originate in the yolk sac wall, migrate into the embryo, and enter the primary sex cords to give rise to the ova.

Development of the Ovaries

• Female Differentiation: In embryos with a double "X" chromosome (female), gonad differentiation occurs later than in males.

• Rete Ovarii: Primary sex cords converge to form a network of canals called the rete ovarii, which soon disappear along with the primary sex cords.

• Cortical Cords: Concurrently, the surface epithelium of the developing ovary forms secondary sex cords, or cortical cords (Figure 28-2).

• Primordial Follicles: As cortical cords grow, primordial germ cells are incorporated. Around 16 weeks of gestation, cortical cords break into isolated cell clusters called primordial follicles. Each follicle contains an oogonium (derived from a primordial germ cell) surrounded by a layer of flattened follicular cells (derived from surface epithelial cells in the cord).

• Oogonia Development: Oogonia multiply rapidly by mitosis, producing thousands of primitive germ cells. Before birth, most oogonia enlarge to form primary oocytes, which enter the first meiotic prophase and remain arrested until puberty.

Development of the Genital Ducts

• Indifferent State: All embryos initially have identical pairs of genital ducts (paramesonephric/Mullerian ducts for females and mesonephric/Wolffian ducts for males).

• Sexual Determination: While genetic sex is determined at fertilization, morphological indications of maleness or femaleness are not apparent until the 9^{th} gestational week.

• Female Duct Development: The paramesonephric ducts form most of the female genital tract:

  • Cranial Parts: Develop into the uterine tubes.

  • Caudal Parts: Fuse to form the uterovaginal primordium (or canal), which develops into the uterus and part of the vagina.

  • Vagina Formation: Contact of the uterovaginal primordium with the urogenital sinus induces the formation of paired endodermal outgrowths called sinovaginal bulbs. These bulbs fuse to form a solid vaginal plate. The central cells of this plate break down to form the vagina, and the peripheral cells form the vaginal epithelium.

Development of the External Genitalia

• Indifferent Stage: Both sexes appear similar early in development, until the 9^{th} week of gestation.

• Completion: External organs are fully developed by the 12^{th} week (Figure 28-3).

• Structures:

  • Urethra and vagina open into the urogenital sinus, which becomes the vestibule of the vagina.

  • Urogenital folds transform into the labia minora.

  • Labioscrotal swellings become the labia majora.

  • The phallus develops into the clitoris.

Normal Sonographic Appearance of the Pediatric Female Pelvis

Bladder

• Normal Appearance: Smooth, thin wall.

• Wall Thickness:

  • When distended (top of bladder exceeds uterine fundus): wall thickness should be less than 3\ mm, with a mean of 1.5\ mm.

  • When empty or partially full: wall appears thicker but should not exceed 5\ mm.

• Ureters: Distal ureters are not routinely visualized unless dilated. Color Doppler can show ureteral jets; angle the probe caudally towards the bladder base with slightly high gain and hold still.

• Bladder Neck and Urethra: May be demonstrated by angling the transducer inferiorly. Perineal or transrectal approaches are useful for urethral abnormalities.

• Hydrosonourethrograpy: Used for anterior urethral abnormalities such as strictures, calculi, urethral valves, diverticula, and trauma.

• Postvoid Scan: Useful for assessing bladder emptying and differentiating the bladder from a pelvic cyst.

Uterus

• Newborn Female:

  • Appearance: Prominent and thickened, with a brightly echogenic endometrial lining due to in utero hormonal stimulation (Figure 28-4).

  • Shape/Size: Pear-shaped, approximately 3.5\ cm in length. Fundus-to-cervix ratio is 1:2 (the fundus is smaller than the cervix).

  • Regression: As maternal hormones decrease after birth, uterine size also decreases. It assumes a teardrop shape with the cervix consuming more area than the fundus.

• Prepubertal (after 2 to 3 months of age):

  • Size/Shape: Regresses to a prepubertal size, 2.5\ to 3\ cm in length, and has a tubular configuration.

  • Fundus-to-Cervix Ratio: 1:1. Endometrial stripe echoes are typically not visualized. Some endometrial fluid may be present.

• **Postpubertal (after age 7 years, greatest increase after puberty):

  • Size/Shape: Uterus increases in size and dramatically changes shape. The fundus becomes much larger than the cervix. Length increases to 5\ to 7\ cm.

  • Fundus-to-Cervix Ratio: 3:1.

  • Endometrial Lining: Echogenicity and thickness vary according to the phase of the menstrual cycle.

• Blood Supply: Supplied by bilateral uterine arteries (branches of the internal iliac arteries). Color flow Doppler may demonstrate flow in the myometrial tissue with little or no flow in the endometrium.

Table 28-1: Uterine Measurements

Vagina

• Examination: Physical examination is difficult in young patients and often requires general anesthesia for suspected anomalies.

• Sonographic Imaging: Best imaged on a midline longitudinal view when the bladder is very distended.

• Appearance: Appears as a tubular structure posterior to the bladder and is continuous with the uterine cervix. The mucosal walls produce a bright central echo.

Ovary

• Evaluation Challenges: Variable location, size, and patient age make evaluation challenging.

• Neonatal Location: May be found anywhere between the lower pole of the kidneys and the true pelvis.

• Ovarian Volume Calculation: Most accurate using the prolate-ellipse formula:
  Volume (cm^3) = Length imes Height imes Width imes 0.523

• Mean Ovarian Volume: Stable up to 5\ years (0.75 to 0.86\ cm^3) and then gradually increases until puberty.

• Texture: Usually homogeneous, but small follicles may be seen. In the neonatal period, the ovary appears heterogeneous due to tiny cysts. Larger cysts are more common after the first year of life.

• Blood Supply: From the ovarian artery (originates directly from the aorta) and from the uterine artery (supplies an adnexal branch to each ovary).

Table 28-2: Ovarian Volume Measurements (Premenarchal)

Pathology of the Pediatric Genital System

Congenital Anomalies of the Uterus and Vagina

• Diagnosis: Requires visualization of uterine cavity/cavities and serosal margin(s). Historically, hysterosalpingography with laparoscopy was used; now, transabdominal and transvaginal ultrasound are key.

• Sonohysterosalpingography: In older patients, involves injecting contrast material into the cavity to differentiate the uterine cavity and septa.

• Clinical Significance: Developmental problems, blood supply interference, or distortion of the uterine cavity can lead to infertility or spontaneous abortion. These anomalies occur in approximately 0.5\% of females and are associated with increased incidence of abortion and obstetric complications.

• Presentation: Not common in children, usually presenting as an abdominal or pelvic mass due to obstruction. There is a high association with renal anomalies when uterine cavity abnormalities are discovered.

• Embryological Origin: The uterus and upper third of the vagina derive from the embryonic Mullerian (paramesonephric) ducts. These ducts must elongate, fuse, and form lumens between the 7^{th} and 12^{th} weeks of embryonic development. Failure results in various Mullerian abnormalities.

Sonographic Findings for Mullerian Anomalies

• Associated Renal Anomalies: If Mullerian anomalies are found, the kidneys should be examined for ipsilateral renal agenesis or morphological abnormalities, as these conditions are commonly associated (Figure 28-5).

• Uterine Malformations: Suspected based on abnormal uterine configuration on pelvic sonograms.

Mullerian Anomalies Classification

These are classified into six groups based on prognosis for future fertility and surgical correction (Figure 28-6):

• Class I: Segmental Mullerian Agenesis or Incomplete Vaginal Canalization

  • Presentation: Suspected when a young girl reaches puberty without menstruation (amenorrhea).

  • Conditions: Transverse vaginal septum or vaginal atresia.

  • Diagnosis: Diagnosed by the development of hydrocolpos (fluid-filled vagina), hydrometrocolpos (fluid-filled vagina and uterus), or hematometrocolpos (blood-filled vagina and uterus) (Figure 28-7).

  • Sonographic Findings: The cervix may be absent, with or without blood in the uterine or cervical cavities. This condition may present in the neonatal period as a large cystic pelvic-abdominal mass due to maternal hormonal stimulation or is discovered at puberty. Also results from an imperforate hymen.

• Class II: Unicornuate Uterus

  • Description: A long, slender (cigar-shaped) uterus deviated to one side.

  • Clinical Impact: Related to infertility and pregnancy loss.

  • Associated Anomalies: Usually, renal agenesis is apparent on the contralateral side.

  • Sonographic Challenge: Difficult to differentiate from a normal uterus by sonography; suspected when the uterus appears small and laterally positioned.

• Classes III through V:

  • Complexity: More difficult to diagnose as they all feature two uterine cavities.

  • Diagnosis: Correct classification and treatment depend on the external contour of the uterine fundus.

  • Mimicry: In a non-pregnant state, a congenital malformation can be difficult to demonstrate and may mimic a fibroid.

• Class III: Uterus Didelphys

  • Description: Complete duplication of the uterus, cervix, and vagina.

  • Clinical Impact: Not usually associated with fertility problems and generally does not require treatment.

  • Sonographic Findings: Detects two endometrial echo complexes, best demonstrated during the secretory phase of the menstrual cycle when the endometrium is most prominent. The external contour of the uterus helps distinguish it from septate and bicornuate uteri.

• Class IV: Bicornuate Uterus

  • Description: A uterus with duplication of the uterine cavity and a common cervix (Figure 28-8). It has wide-spaced cavities and a low incidence of fertility complications, usually not treated. The image looks heart-shaped on the transverse plane.

  • Exception for Treatment: A rudimentary and noncommunicating horn. If an embryo implants in this cavity, it may grow until about 12 to 16 weeks, potentially leading to uterine rupture.

  • Diagnosis: Often diagnosed incidentally in early pregnancy when a gestational sac is present in one horn and a decidual reaction in the other.

• Class V: Septate Uterus

  • Description: Two uterine cavities closely spaced, with one fundus and sometimes two cervical canals or a vaginal septum.

  • Clinical Impact: Has the highest incidence of fertility problems. The septum may be removed hysteroscopically.

• Class VI: Diethylstilbestrol (DES) Exposure

  • Cause: Related to in utero exposure to DES, a synthetic estrogenic drug used extensively in the 1970s to treat threatened and habitual abortion.

  • Impact: Estimated 5 to 10 million Americans received the drug during pregnancy. It was later found to cause vaginal malignancies in the daughters of mothers who were given the drug.

  • Sonographic Findings: The uterus is normal in size and shape externally, but the cavity is “T”-shaped with an irregular contour. This condition can be difficult to diagnose with ultrasound.

Ambiguous Genitalia

• Definition: Errors in sexual development resulting in ambiguous genitalia or hermaphroditism.

• True Hermaphrodites: Possess both ovarian and testicular tissue. Internal and external genitalia are variable. Most have a 46,XX karyotype; some are mosaics (46,XX/46,XY).

• Female Pseudohermaphrodites (46,XX karyotype):

  • Most Common Cause: Congenital virilizing adrenal hyperplasia, leading to increased androgen production and masculinization of external genitalia (enlarged clitoris, urogenital sinus abnormalities, and partial fusion of the labia majora).

  • Other Causes: External genitalia masculinization can also occur via androgenic hormones reaching the fetal placenta if the mother’s suprarenal cortices are overactive or if she received hormone therapy involving androgenic substances.

• Sonographic Findings: Sonography aids in identifying the presence or absence of the uterus, vagina, and ovaries in utero or in neonates. In utero cases can be challenging if clear images of the genital area cannot be made. Sex assignment relies on karyotype analysis, gonadal biopsy, and genital anatomy knowledge.

Precocious Puberty

• Classification: True precocious puberty or precocious pseudopuberty.

• True Precocious Puberty:

  • Isosexual: Always involves the development of secondary sexual characteristics of the same sex.

  • Gonadal Activity: Increased size and activity of the gonads.

  • Sonographic Findings: Uterus has an enlarged, postpubertal configuration (fundus-to-cervix ratio is 2:1 or 3:1) with an echogenic endometrial canal. Ovarian volume is enlarged (>1\ cm^3), and functional cysts are often present.

• Precocious Pseudopuberty:

  • Characteristics: Maturation of secondary sexual characteristics but without gonad activation (no activation of the hypothalamic-pituitary-gonadal axis).

  • Most Common Cause: Excessive exogenous synthesis of gonadal steroids (from adrenal gland, tumors, or cysts).

  • Induced Precocious Puberty: Prolonged exposure to exogenous gonadal hormones can mature the central nervous system and cause true precocious puberty in some children.

  • Sonographic Findings: Useful to detect a pelvic mass and a mature uterus; determine volume and size of ovaries, uterus, and cervix; and exclude an ovarian neoplasm. Liver and adrenal glands should also be assessed to rule out lesions causing precocious puberty.

Pathology of the Pediatric Ovary

• Ovarian Development: Begins in the fetal gestational period and continues dynamically through childhood.

• Neonatal Ovaries: Similar in function and anatomy to pubertal and adult ovaries.

• Common Pathologies: Ovarian cyst, ovarian torsion, and ovarian teratoma development (Table 28-3).

• Normal Neonatal/Infant Ovary: Heterogeneous and cystic on ultrasound. Most cysts are less than 9\ mm in diameter, with the mean diameter of the largest cyst measuring 7.5\ mm. These cysts develop from ovarian follicles.

• Pathologic vs. Physiologic Cysts: Cysts larger than 2\ cm are considered pathologic.

• Factors Contributing to Follicular Growth In Utero: Follicle-stimulating hormone (FSH), maternal estrogens, and human chorionic gonadotropin (hCG).

  • Primary Stimulus: FSH, secreted by the pituitary gland, increases the number and size of small follicles.

  • Third Trimester: Other hormones contribute to further follicular growth.

• Post-Birth Hormonal Changes: At birth, maternal estrogens and hCG levels fall with placental separation. FSH levels decline due to the inhibitory mechanism of the hypothalamus-pituitary-ovary axis.

Neonatal Ovarian Cysts

• Origin: May result from disordered folliculogenesis in the fetal ovary. Most fetal cysts resolve spontaneously but can persist into the neonatal period.

• Common Findings: Small follicular cysts of 3 to 7\ mm are common and normal.

• Pathologic Varieties: Follicular, corpus luteum, and theca lutein cysts (due to excessive stimulation of the fetal ovary by placental and maternal hormones).

• Increased Incidence: Higher incidence of larger ovarian cysts in infants of mothers with toxemia, diabetes, and Rh isoimmunization, all associated with greater release of placental chorionic gonadotropin.

• Hypothyroidism Link: Follicular cysts are described in maternal and congenital hypothyroidism, explained by nonspecific pituitary glycoprotein hormone synthesis.

Complications

• Most cysts regress spontaneously. If persistent, complications include hemorrhage and salpingotorsion.

• Torsion: More common in larger cysts. Clinically, patients present with pain, vomiting, fever, abdominal distention, leukocytosis, and peritonitis.

• Hemorrhage: Can result from torsion or occur spontaneously in a nontwisted cyst. Rupture can lead to hemorrhagic ascites or peritonitis.

• Large Cyst Complications: Bowel obstruction, thorax compression with pulmonary hypoplasia, urinary tract obstruction, or incarceration with an inguinal hernia.

Sonographic Findings

• Size: Varies greatly; larger cysts may occupy nearly the entire abdomen, compressing normal organs (Figure 28-9).

• Appearance: Can be completely anechoic with well-defined borders. If hemorrhage occurs, internal echoes are seen.

• Complicated Cysts: May contain a fluid-debris level, a retracting clot, or septa. Can also be completely filled with echoes, appearing as a solid mass.

Differential Considerations

• Sonography characterizes the mass, but histologic confirmation (biopsy) is required for diagnosis.

• Difficult Differentiation: Separating an ovarian cyst from a mesenteric or enteric duplication cyst can be difficult if the cyst is large and displaces or distorts the normal ovary.

• Other Abnormalities: Hydrometrocolpos, cystic meconium peritonitis, urachal cysts, and anterior meningocele.

• Rare Neoplasms: Cystadenoma, cystic teratomas, and granulosa cell tumors are rare in neonates.

Ovarian Torsion

• Incidence: Can occur at any age, but most cases are within the first two decades of life.

• Mechanism: Normal adnexa in young girls can be mobile, allowing torsion at the mesosalpinx due to changes in intra-abdominal pressure or body position.

• Location: The ovary is extrapelvic in neonates and infants, while in older children, the mass is in the adnexal area. More common when ovarian cysts or tumors are present.

• Pathophysiology: Partial or complete rotation of the ovary on its vascular pedicle compromises both arterial and venous flow, leading to congestion of ovarian parenchyma and eventually hemorrhagic infarction.

• Clinical Symptoms: Severe onset of abdominal pain. In infants, this symptom may go unrecognized, potentially leading to necrosis if surgical intervention is delayed.

• Differential Diagnosis (Lower Abdominal Pain): Appendicitis, gastroenteritis, pyelonephritis, or pelvic inflammatory disease.

Sonographic Findings

• Nonspecific Findings: May include enlargement of the affected ovary (Figure 28-10), fluid in the cul-de-sac, and other adnexal pathologies like a cyst or tumor.

• Specific Sign: Demonstration of multiple prominent follicles (>8 to 12\ mm) in the cortical (peripheral) portion of a unilaterally enlarged ovary has been reported as a sonographic sign of torsion, correlating with pathological evidence of ovarian hemorrhage or infarction.

• Color Doppler: Variable and not specific, as arterial blood flow depends on the extent of torsion (complete or incomplete).

• Late Manifestation: Fluid in the cul-de-sac is typically a late manifestation of ovarian torsion.

• Amputation: If torsion and subsequent amputation occur, the ovary may detach from the adnexa and migrate to other abdominal sites. This mass is often pedunculated with mesentery and omentum and may calcify later, visible on radiograph.

Ovarian Teratomas

• Incidence: Uncommon in neonates and adolescents. Germ cell tumors account for 60\% of ovarian neoplasms in patients younger than 20\ years of age.

• Spectrum: Ranges from benign mature teratomas to malignant varieties (dysgerminomas, immature teratomas, embryonal carcinomas, endodermal sinus tumors, choriocarcinomas, and mixed tumors).

• Most Common: The benign mature teratoma, or dermoid cyst, is the most common pediatric germ cell tumor.

Sonographic Characteristics of Benign Teratomas

• Wide Spectrum: Exhibit a wide spectrum of sonographic characteristics.

• Typical Appearance: A central cystic cavity filled with sebaceous debris, surrounded by various skin appendages, a squamous epithelial layer, and a thick capsule (Figure 28-11).

• Dermal Plug/Mural Nodule: A nubbin of tissue frequently found in the wall.

• Other Findings: May include a solid or complex mass with fat-fluid levels, hair-fluid levels, and calcification.

• Size: Most dermoid tumors range between 5 and 15\ cm in size.

Clinical Presentation

• Asymptomatic: Most patients with dermoid tumors are asymptomatic.

• Pain/Distention: Abdominal pain or distention may occur when the tumor becomes large.

• Complication: Torsion: The most frequent complication (in 16\% to 40\% of cases). Pain may mimic appendicitis if located on the right side of the abdomen.

Sonographic Findings

• Appearance: Recognized as a complex mass with a heterogeneous appearance (Figure 28-12).

• Key Features: Mural nodules and echogenic foci with acoustic shadowing are typical findings.

• Age-Related Shadowing: In the neonatal period, less shadowing is seen in the lesion compared to when observed in adolescent girls.

The Scrotum

• Examination in Neonates: Performed with a high-frequency linear array transducer for optimal resolution and widest field of view.

• Pediatric Scrotum Evaluation: High-frequency curvilinear array transducer.

• Palpation: Scrotum should be carefully palpated for abnormalities in the scrotal parenchyma.

• Positioning: A small towel may be placed vertically between the legs, under the scrotal sac, to elevate and immobilize the testes.

• Stand-off Pad: If the scrotum is red and painful, a stand-off pad may be used.