Picture of the Month Quiz
A 3-week-old boy presented to the emergency department with an unusual pattern of purulent drainage and crusting overlying an area of fluctuance on the posterior scalp. The patient was delivered via emergent cesarean section at 41 weeks' gestation owing to fetal heart decelerations. The patient's mother reported persistent pelvic pressure for at least 12 hours prior to cesarean section. The infant had caput succedaneum and extensive cranial molding on delivery. When discharged to home, the patient’s mother noted a light brown line of scar that circumscribed the head. The posterior occipital part of this line developed an area of redness that enlarged and became crusted and fluctuant over several days. There was no fever, the patient was feeding well, and energy levels and urine output were unchanged. The patient was sent to the emergency department by his pediatrician to rule out infection.
On presentation, the patient was afebrile; physical examination results were notable only for an annular hyperpigmented alopecic plaque that extended from posterior auricular areas (Figure, A and B) with crusting and underlying fluctuance and erythema over the left posterior scalp (Figure, C). Evaluation included a scalp ultrasonograph that demonstrated a multilobular heterogeneous collection superficial to the calvarium and musculature on the posterior scalp. The white blood cell count was 15 x 103/µL, with no evidence of left shift. A scalp culture of the purulent drainage yielded coagulase-negative staphylococci, and a blood culture showed no growth.
What is your diagnosis?
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