Case #07 Discussion:

What is the differential diagnosis for abdominal distension in a young female?

(1) Pregnancy: The most frequent cause of abdominal distension in a young female, this is not viable in her case owing to her regular menstruation and lack of elevated ß-HCG or AFP. Molar pregnancy or gestational trophoblastic moles occur frequently in women under 29 years of age, but can also be ruled out in this case by the low ß-HCG .

(2) Small bowel obstruction: Massively dilated loops of small bowel can distend the abdomen secondary to obstruction. However, in this case, no GI symptoms are reported and the pain is not periumbilical as one would expect from midgut pathology. Although acute appendicitis is associated with RLQ pain and can cause SBO, this diagnosis is not consistent with the chronology of her history (distension preceding pain).

(3) Hepatosplenomegaly: Enlarged liver and/or spleen may increase abdominal girth and can result from a variety of disease processes. Although liver pathology would be more likely to evoke RUQ than RLQ pain, it should remain on the differential. Splenomegaly often accompanies hepatomegaly and should also be ruled out.

(4) Ascites: Serous fluid in the abdomen may result from cirrhosis, hypoproteinemia, or congestive heart failure. In a young, well-nourished female the latter two are not particularly likely diagnoses; however, cirrhosis can occur at a young age secondary to viral or autoimmune hepatitis, as well as alpha-1-antitrypsin deficiency. Exudative ascites may occur with inflammatory conditions, such as abscess, pancreatitis, peritonitis, or bowel perforation; however, these are not likely in this case as the patient is not febrile or toxic appearing, has no GI involvement, and does not have an acute abdomen. Neoplastic ascites associated with an intraperitoneal tumor is another diagnostic possibility. Ruling out ascites is an important diagnostic measure in this case.

(5) Abdominal mass: Increased abdominal girth associated with localized pain suggests involvement of an abdominal organ, either directly or secondary to impingement by mass effect. In particular, RLQ pain in a female may signal involvement of pelvic organs, such as ovaries and uterus.

The most common ovarian masses in children and adolescents are simple follicular and corpus luteum cysts, and these occasionally grow up to 20 cm secondary to accumulation of fluid or internal hemorrhage. Ovarian tumors include serous and mucinous cystadenoma and cystadenocarcinoma (epithelial tumors), as well as benign cystic teratomas (dermoid cysts) and the less common malignant germ cell and stromal tumors. Benign cystic teratomas (germ cell tumors) are the most common ovarian neoplasm and predominate in females 10-30 years of age. Although stromal tumors predominate in the first three decades of life, they are typically slow growing which is inconsistent with this patients history. Benign epithelial tumors are also frequent in young women, and epithelial tumors of borderline malignancy may occur. The low CA125 is also somewhat reassuring against ovarian cancer, although it is more likely to be elevated with serous than mucinous forms. In addition, cystadenocarcinomas of the ovary are rare in the pediatric population, affecting predominantly women in late middle age. Likewise, the low AFP level points away from germ line tumors but does not rule them out.

Malignant uterine neoplasms are uncommon in children; however, rhabdomyosarcoma may arise from the anterior wall of the vagina and extend upwards into the pelvis. Leiomyoma is a common benign tumor of smooth-muscle origin that arises in the uterine myometrium and may be large and fast growing, consistent with this patient's history. Non-gynecologic pelvic masses include para-ovarian cysts in the mesosalpinx arising from wolffian duct remnants, as well as mesenteric and omental cysts. Other abdominal masses to consider include abdominal lymphoma, hepatocellular carcinoma (unlikely given low AFP), hepatic adenoma, and hemangioma. Renal and adrenal masses, such as Wilm's tumor and neuroblastoma are also possibilities but these are more common in the younger pediatric population (< 5 y/o).

What is the appropriate approach to diagnostic imaging in this case?

Ultrasound (US) is useful for visualizing abdominal and pelvic organs and is the primary imaging modality for evaluating the female genital tract and pelvis. Non-invasive imaging of liver, kidneys and spleen is possible while confirming the existence of a pelvic mass by US, as well as visualizing its size, contour and character, and detecting ascites. Ovarian masses, being primarily cystic in nature, are particularly well visualized by US and may be classified as simple (unilocular) or complex (multilocular with internal septations). CT can be useful for further characterization, sizing, and localization of a mass detected by US, as well as for determination of secondary involvement of other structures. Ovarian masses can be difficult to distinguish from bowel by MRI. Benign cystic adenomas may also be diagnosed by plain Xray, provided the pathognomonic finding of well-formed teeth is present. In the case of solid pelvic masses, such as leiomyomas, MRI offers better visualization than US.

Outcome

This patient underwent exploratory laparotomy with removal of a 30 pound turgid cyst that measured 36.5 cm x 32 cm x 22 cm and had a normal fallopian tube attached. Note how similar the actual size of the cyst is to the measurements based on the CT image. The cyst had a smooth tan-white to purple- black surface with multiple scattered surface vessels and was sectioned to reveal a multiloculated structure with the largest compartment measuring 20 cm in diameter. Histopathological analysis confirmed a benign mucinous cystadenoma of the left ovary.