The normal prostate gland and seminal vesicles are usually too small to identify on routine pelvic CT in infants and young boys. As these structures increase in size at the time of puberty, they are easier to recognize. The prostate gland lies posterior to the symphysis pubis and anterior to the
rectum, appearing as a homogeneous, rounded soft tissue structure on both unenhanced and enhanced CT scans. Zonal anatomy is usually not seen on CT (Fig. 11.3A).

The paired seminal vesicles lie posterior to the urinary bladder, cephalad to the prostate gland, and anterior to the rectum. They have soft tissue attenuation and a characteristic oval or bow tie configuration (Fig. 11.3B). The spermatic cords lie anterolateral to the symphysis pubis and medial to the femoral veins. They appear as oval or round, homogenous soft tissue structures (Fig. 11.3A) or
as thin-walled, ringlike structures containing fat and small dots, representing spermatic vessels and the vas deferens. Normal testes are easily seen in the scrotum as homogeneous oval structures.

The urinary bladder is a midline structure with varying size and configuration depending on the degree of distention. The bladder wall is thin and has attenuation equal to that of soft tissue. Unopacified urine has attenuation similar to that of water (Fig. 11.2A).

The pelvic muscles (psoas, iliacus, obturator internus, pyriformis, and levator ani) are symmetrical in size and shape in normal individuals. Small bowel loops; the ascending, descending, and sigmoid colon; and the rectum are easily seen on CT, especially when the bowel lumen is distended with contrast, air, or fecal material. Normal pelvic lymph nodes are not routinely recognized on CT scans in infants and young children. Small nodes, <10 mm in short axis, may be seen in adolescents.

The müllerian ducts are paired structures that form the uterus, cervix, fallopian tubes, and upper one third of the vagina. The lower two thirds of the vagina develop from the urogenital sinus. Anomalies occur in 0.1% to 0.5% of the general population (10,12,14). They result because of failed development or fusion of the müllerian ducts or from failure of septal resorption once fusion has occurred (Fig. 11.4).

Functional cysts, which include follicular, corpus luteum, and hemorrhagic cysts, result from normal ovarian function. They can occur in neonates and adolescents. In neonates, they result from exaggeration of normal follicular development secondary to in utero stimulation by maternal hormones. In pubertal girls, they result when a follicular cyst continues to grow after ovulation or when a corpus luteum fails to involute. CT is usually not needed for diagnosis, but recognition of the appearance of ovarian cysts on CT is important because they are often incidental findings on studies obtained for other indications. In patients with large ovarian cysts, CT may be useful to document the exact extent of the cyst prior to aspiration or surgery.

Functional cysts range in size from 3 to 20 cm, but most measure between 3 and 5 cm. At CT, the uncomplicated ovarian cyst appears as a well-circumscribed, low-attenuation (<20 HU) unilocular mass with thin or barely perceptible, nonenhancing walls (Fig. 11.6). Higher attenuation, internal fluid–debris levels or septa, or thick walls should raise the suspicion of a hemorrhagic cyst (Fig. 11.7). A hemorrhagic cyst develops when blood vessels within a follicular or corpus luteum cyst rupture. These cysts can produce acute abdominal pain. Acute hemorrhage has a high attenuation value; old blood has an attenuation value nearer that of water. Follicular and corpus luteum cysts cannot be reliably differentiated on the basis of the CT findings alone. Most follicular and corpus luteum cysts <5 cm in diameter involute within 1 or 2 menstrual cycles. Larger cysts may or may not regress.

Most predominantly solid ovarian tumors are malignant. Tumors of germ cell origin constitute 60% to 90% of malignant neoplasms. Stromal tumors account for 10% to 13% of malignant tumors, and epithelial carcinomas for 5% to 11% of tumors (19,20,21,22).

Secondary involvement of the ovary can result from contiguous spread from adjacent neoplasms or from lymphatic dissemination. Tumors that metastasize to the ovaries include neuroblastoma, lymphoma, and leukemia. Metastatic involvement is usually asymptomatic, and the diagnosis is made at autopsy. Rarely, the tumors are large enough to produce a palpable mass. On CT, metastases may appear as a diffusely enlarged ovary or as a discrete mass.

Pelvic inflammatory disease affects girls of reproductive age and usually results from an ascending infection by Neisseria gonorrhoeae or Chlamydia trachomatis (42). The inflammatory process begins in the vagina and cervix and then ascends to the endometrium and fallopian tubes, where it can then spread to the ovaries, parametrium, and peritoneal cavity. The diagnosis is usually made clinically, based on symptoms of pelvic pain, vaginal discharge, fever, and cervical motion tenderness. CT is useful to identify complications, such as pyosalpinx and tubo-ovarian abscess (43,44,45).

Pyosalpinx tends to be tubular (Fig. 11.22), whereas tubo-ovarian abscess has a round or oval configuration (Fig. 11.23). Both lesions usually have low-attenuation centers and thick walls that enhance following the administration of intravenous contrast medium. They also may exhibit soft tissue septations, air, and a fluid–debris or air–fluid level. Other findings are related to the underlying pelvic inflammatory disease and include soft tissue stranding or haziness of the pelvic fat with obscuration of the pelvic fascial planes, adjacent thickening of the uterosacral
ligaments, narrowing or irregularity of the rectosigmoid colon, hydronephrosis and hydroureter, and lymphadenopathy (43,44,45).

Torsion of the ovary and fallopian tube results from partial or complete rotation of the ovary on its vascular pedicle. The end result is interruption of lymphatic, venous, and arterial flow causing vascular congestion in the ovarian parenchyma and eventually hemorrhagic infarction. The underlying adnexum may be normal or it may contain a cyst or tumor that acts as a fulcrum to potentiate twisting of the ovary and fallopian tube. Pathologic lesions are more common in neonates and infants than they are in adolescent girls. In one series of 20 patients, approximately 65% of neonates but only 10% of pubertal girls had abnormal ovaries (46). The most likely explanation for torsion of a normal adnexum is excessive mobility secondary to lax supporting ligaments. Adnexal torsion is nearly always unilateral. Bilateral torsion is usually asynchronous.

Adnexal torsion occurs in all age groups, but it is more common in adolescents and young women. Typically, patients present with acute lower abdominal pain, often associated with nausea, vomiting, and leukocytosis. A history of previous episodes of similar pain, thought to reflect intermittent torsion and detorsion, is common. The diagnosis of torsion is usually established on sonography, but torsion may be unexpectedly encountered on CT performed for evaluation of acute lower abdominal or pelvic pain.

The characteristic CT features of torsion of a normal ovary are a markedly enlarged ovary containing multiple, peripheral cystic structures, representing dilated follicles (Fig. 11.24) (47). The torsed ovary is usually three to four times larger than the normal ovary. It often assumes a midline position, either behind the bladder or cephalad to the uterus. Other common CT findings of torsion include engorged ipsilateral parametrial vessels,
a thickened fallopian tube, uterine deviation to the twisted side, complete absence of enhancement of the torsed ovary, and ascites (48,49,50). An underlying ovarian abnormality, such as a cyst or tumor, may be seen in some cases (Fig. 11.25).

Gestational trophoblastic disease can be a cause of an intrauterine mass in an adolescent girl. It represents a spectrum of diseases ranging from the relatively benign hydatidiform mole to the malignant invasive mole or choriocarcinoma. The clinical findings of gestational trophoblastic disease are vaginal bleeding and elevated serum human chorionic gonadotropins levels. CT is useful to detect local or metastatic spread of tumor in patients with invasive molar disease or choriocarcinoma (16,17).

CT findings of gestational trophoblastic disease include an enlarged, thick-walled uterus, a heterogeneously enhancing mass in the endometrial cavity, and hypoattenuating myometrial nodules, representing tumor or areas of hemorrhage or necrosis (Fig. 11.26) (16,17). Additional findings include a gestational sac with or without a small fetal pole; dilated, tortuous parametrial vessels; and bilaterally enlarged ovaries that contain theca-lutein cysts. Metastases to liver and lung also may be seen.

Endometriosis is a gynecologic condition that is characterized by the presence of ectopic endometrial glands and stroma in abnormal locations. There are two forms: external (outside the uterus) and internal (intrauterine). The intrauterine form is termed adenomyosis. Both forms can occur in any menstruating female. The typical symptoms include pelvic pain, dysmenorrhea, and menorrhagia. The CT appearance of adenomyosis is focal thickening of the myometrium or uterine wall. The lesion can appear solid or cystic. Cystic adenomyosis is the result of multiple episodes of bleeding (Fig. 11.27) (51).

Leiomyomas (fibroids) arise from the overgrowth of smooth muscle and connective tissue in the uterus. Most occur in the fundus and body of the uterus, are intramural, and are located in the myometrium. Characteristic CT findings are an enlarged uterus and a deformed lobulated uterine contour (52). They typically have soft tissue attenuation similar to that of normal uterus and show contrast enhancement similar to that of normal myometrium. Hypoattenuating areas, representing hemorrhage or necrosis, and calcification may also be seen. Differentiation between leiomyoma and adenomyosis can be difficult on CT and may require MRI or biopsy.

Rhabdomyosarcoma is the most common tumor of the genitourinary tract in children, accounting for 5% to 15% of all malignant solid tumors in patients younger than 15 years of age (53,54,55). The tumor has a bimodal age distribution, with the first peak occurring between 2 and 6 years of age and the second peak between 14 and 18 years of age. The embryonal and botryoid subtypes are the predominant histologic subtypes in the genitourinary tract.

Boys with prostate tumors usually present with urinary retention, flank pain related to hydroureter or hydronephrosis, or constipation. Girls with vaginal rhabdomyosarcoma come to clinical attention because of vaginal bleeding or a mass that prolapses into the introitus or onto the perineum. Rhabdomyosarcoma spreads by direct extension to contiguous structures or by hematogenous or lymphatic dissemination to lymph nodes, lungs, bone, bone marrow, or liver (53,54,55). The role of CT is to characterize the mass and determine the presence or absence of local invasion into pelvic fat, lymph nodes, or adjacent viscera and also distant metastatic disease for staging, treatment planning, and assessing prognosis.

At CT, prostatic and vaginal rhabdomyosarcomas appear as bulky soft tissue masses (Figs. 11.28 and 11.29) (53,54). They may exhibit calcifications and cystic areas, representing hemorrhage or necrosis. Hydronephrosis is common with both tumors. Other findings associated with prostatic rhabdomyosarcoma are an elevated bladder base or bladder wall invasion and an elongated prostatic urethra. Secondary findings in vaginal rhabdomyosarcoma are a dilated, fluid-filled endometrial cavity and uterine enlargement.

Findings indicating regional tumor spread include lymph node enlargement and a soft tissue mass extending from the prostate or vagina into adjacent viscera, muscles, or perivisceral fat (Figs. 11.28 and 11.29). The presence of fat planes between the neoplasm and adjacent structures militates against gross invasion, but the absence of fat planes may be normal or due to tumor adherence or invasion. When the loss of fat planes is associated with an eccentric soft tissue mass, a confident diagnosis of extravaginal or prostatic extension can be made.

The prostatic utricle, which is a remnant of the müllerian ducts, opens into the center of the prostatic urethra. It can become visibly enlarged in patients with hypospadias, ambiguous genitalia, and undescended testes (56). Complications are rare, but calculi may develop within the cysts and they may be associated with persistent infections. At CT, the utricle appears as a round of oval, low-attenuation structure extending posterior to the prostate in the expected area of the urethra (Fig. 11.30).

Seminal vesicle cysts are usually found in association with urinary tract anomalies or autosomal dominant polycystic disease. The associated anomalies include renal agenesis, renal hypoplasia, and duplication of the collecting system with ectopic ureteral insertion into the bladder neck, prostatic urethra, or seminal vesicles (57). On CT, seminal vesicle cysts appear as low-attenuation masses posterior to the urinary bladder and cephalad to the prostate gland (Fig. 11.31).

CT is not needed to diagnose bladder inflammation. However, on studies obtained for other clinical indications, CT may show focal or diffuse bladder wall thickening or a polypoid mass (inflammatory pseudotumor) caused by cystitis. Inflammatory wall thickening can be confused with a neoplasm on CT scans (Fig. 11.35). Correlation with clinical history or biopsy of the lesion is usually required for diagnosis.

In utero, the anterior bladder wall and umbilicus communicate with each other via a tubular channel, termed the urachus, which usually closes prior to birth. Failed obliteration of the urachal lumen results in four major types of anomalies: patent urachus—a persistent fistula between the bladder and umbilicus; urachal sinus—persistence of the urachus at its umbilical end; urachal cyst—encapsulation
of fluid in a portion of urachus that is closed at both ends; and urachal diverticulum—persistence of the urachus at its bladder end (61,62). The persistent urachus and the urachal sinus are small-caliber tubular structures that are best evaluated by fistulography. The urachal cyst and diverticulum are closed fluid-filled spaces that can be identified by CT.

The urachal diverticulum arises anteriorly from the bladder dome and will empty when the bladder is decompressed. The urachal cyst appears as a well-circumscribed, thin-walled, near-water-attenuation mass located anteriorly in the midline beneath the rectus abdominis muscle (Fig. 11.36). A high attenuation and/or heterogeneous fluid contents and thick enhancing walls should suggest superimposed infection (pyourachus) (Fig. 11.37). Other findings of pyorurachus include increased attenuation of the subcutaneous or mesenteric fat, rectus muscle thickening, intraperitoneal abscess, and ascites (63).

Sacrococcygeal teratomas are the most common presacral tumor in children (32,65). Four types of sacrococcygeal teratomas have been described based on the relative amounts of internal and external tumor: type I, predominantly external (47%); type II, external and intrapelvic (34%); type III, external, pelvic, and abdominal (9%); and type IV, purely presacral (10%) (Fig. 11.43) (32,65,66,67).

Most sacrococcygeal teratomas are nonfamilial and occur more frequently in females than males (3:1 ratio). Nearly all sacrococcygeal teratomas (>90%) are recognizable in the early neonatal period, presenting as large sacrococcygeal or gluteal masses. The diagnosis may be delayed if the tumors are small and confined to the presacral area. The latter patients usually present in later childhood or adolescence with a history of chronic constipation. The incidence of malignancy varies with the extent of tumor (38% in type IV versus 8% in type I) and with patient age at diagnosis (32,67). The older the patient at the time of diagnosis, the greater is the likelihood of
malignant transformation in the tumor. About 20% of all sacrococcygeal teratomas exhibit malignant elements (32). Malignant tumors metastasize to lung, liver, and lymph nodes.

The diagnosis of sacrococcygeal teratoma is usually obvious when patients present with large pelvic or gluteal masses, but imaging is warranted to determine tumor extent. Benign sacrococcygeal teratomas are chiefly cystic masses with attenuation similar to that of water (Fig. 11.44). They contain <50% solid elements in the form of fat, calcification, bone, or teeth. The solid components can appear as a rounded mass protruding from a cyst wall, as a bridge or band crossing the cyst, or as a thickened segment of cyst wall. Although sacrococcygeal teratomas arise from the coccyx, abnormalities of the spine are uncommon. CT angiography can be useful to show the feeding arteries, which need to be ligated at the time of surgical resection (Fig. 11.44C).

When the volume of soft tissue elements is >50%, the tumor is more likely to be malignant (Fig. 11.45) (66,67).
Calcifications, common in benign teratomas, are less frequent in the malignant forms. Signs of local extension include invasion of adjacent organs, muscles, or soft tissues and lymphadenopathy (Fig. 11.46). Metastases are to lung and occasionally to liver or retroperitoneal lymph nodes. Following treatment, malignant sacrococcygeal tumors may regress entirely, leave a small fibrotic mass, or convert to a mature teratoma (68,69).

Other causes of presacral masses in childhood include familial teratoma, neuroblastoma, anterior meningocele, rectal duplication cysts, and lymphoma. Familial teratomas are rare compared with the nonhereditary teratomas. They have a low incidence of malignancy and are entirely presacral in location. Patients usually present with signs and symptoms related to anorectal stenosis, constipation, or perirectal abscess. Calcifications are found in only 5% of hereditary teratomas, but sacral defects are common, occurring in 95% of patients.

Only 2% to 3% of neuroblastomas arise in the pelvis (70). On CT, pelvic neuroblastoma appears as a presacral soft tissue mass with or without areas of necrosis and amorphous, coarse calcifications. Because of its neural origin, neuroblastoma has a tendency to invade the spinal canal (Fig. 11.47). Lymphadenopathy is another common finding.

The anterior meningocele herniates through a congenital defect in the vertebral body (71). It is most common in the sacral region and at the lumbosacral junction. When the contents of the herniated sac contain neural elements in addition to meninges and cerebrospinal fluid, the mass is termed a myelomeningocele; when fat and
cerebrospinal fluid are present, the mass is termed a lipomeningocele. The diagnosis of an anterior meningocele or myelomeningocele can be strongly suspected on conventional radiographs when a presacral mass is seen in association with a scimitar- or crescent-shaped sacrum. Computed tomography can demonstrate the fluid-filled sac of the meningocele, the bony defect in the lumbar vertebra or sacrum, the low-attenuation fatty elements of a lipomeningocele, and the relationship of the lesion to the spine and other structures of the pelvic cavity. Although the diagnosis can be made by CT, MRI is the preferred study to show the soft tissue contents of the herniated spinal sac, especially the presence of a tethered cord and the communication between the meningocele and the thecal sac.

Rectal duplication cysts account for about 10% of all gastrointestinal duplications (72). Characteristic CT findings are a fluid-filled, round or oval mass adjacent to the rectum (Fig. 11.48). The attenuation value of the cyst contents is usually similar to that of water, but it can be higher if the cyst contains blood or proteinaceous material. The cyst walls tend to be thin and regular, but they may be thickened as a result of infection. Rectal duplication cysts may communicate with the colonic lumen.

Lymphomas and chordomas are rare presacral tumors in children. On CT, presacral lymphoma appears as a homogeneous soft tissue mass. The CT appearance is not specific, but the diagnosis can be suspected when there is also widespread retroperitoneal or mesenteric lymphadenopathy or splenomegaly. The CT findings of chordomas are a soft tissue mass with amorphous cartilaginous calcifications. Chordomas typically produce destruction of the sacrum and coccyx.