The knotty problem in an infant girl's groin

Mid-afternoon, and you're working at the pediatric clinic of your university hospital. With the beautiful spring weather outside, you've seen few acute care visits today; itchy eyes and runny noses in otherwise healthy children have established an unusually relaxing pace! Only one patient remains to be seen: a nearly 3-month-old girl whose mother is concerned about a "knot in the baby's groin."

Mom greets you with an uneasy smile as you enter the examination room. "It hasn't gone away," she says. "I think it's gotten bigger."

Instantly, you remember that the last time you saw the infant was four weeks ago-at her 2-month-old health maintenance visit. She had a diaper rash.

Having decided that the inguinal rash was most consistent with a candidal infection and the mass most consistent with a reactive lymph node, you prescribed nystatin cream to be applied until three days after the rash resolved. You instructed the mother to return to the clinic if either the rash or the lymph node persisted for longer than several weeks. Now, four weeks later, she informs you that the rash did indeed improve within a week after the nystatin was started. The mass in the right groin has not disappeared as expected, however; instead, she reports that its size has nearly doubled!

The patient takes her lumps On further questioning, you learn that the mass has been present continuously over the past four weeks. It has remained nontender and does not appear to bother the baby when it is touched or when it is manipulated during a diaper change. The patient has regular, soft, yellow-to-brown bowel movements several times a day; no blood is obvious in the stool. She has had no emesis and has been taking formula well-four ounces every four or five hours. She has still not had a fever.

Today, rectal temperature is 36.4° C; heart rate, 150/min; and respirations, 42/min. Weight is 3.91 kg (between 5th and 10th percentiles for postconceptual age, tracking along her expected growth velocity). Overall, she is alert and active and appears well. The anterior fontanelle is soft; sclerae are clear; and a pupillary red reflex is present bilaterally. Tympanic membranes are unremarkable. Oropharynx is moist with no enanthem. Neck is supple without lymphadenopathy. Examination of the heart and lungs is unremarkable. The abdomen is soft and nontender, with normal bowel sounds and no organomegaly.

When you remove the girl's diaper, you discern the firm, freely mobile subcutaneous mass in the right inguinal region, midline along the path of the inguinal canal. The mass is 2 x 1.5 cm, nontender on palpation and manipulation, nonpulsatile, and lacking overlying skin changes. Turning to the left inguinal region, you palpate two firm, mobile, nontender masses, each 0.5 x 0.5 cm. You find no other palpable masses. Surveying the baby's skin carefully, you find no rashes anywhere. There are several small areas of hypopigmentation along the inguinal creases and inner thighs.

You're intrigued by the persistence of these inguinal masses. As a first step, the mother-20 years old, with negative serologic tests for syphilis, hepatitis B, and HIV infection-recounts her daughter's medical history for you.