A 3-week-old female presented to the emergency department with a 3-day history of a progressively enlarging, erythematous, seemingly painful lump on her back. One week prior, the parents had noticed a small bump at the base of the child’s tailbone. Over the past 3 days, the area had grown significantly. The infant had been otherwise asymptomatic without fevers, taking normal feeds, urinating normally, and no other rashes or lesions had been noted. The parents reported that the child seemed to be fussy anytime when placed on her back, preferring to lie on her abdomen instead.
History and examination
The patient’s history was notable for birth at 36 weeks, 5 days, by cesarean delivery because of maternal preeclampsia and fetal heart rate decelerations. The child then spent 5 days in the neonatal intensive care unit (NICU) for observation of neonatal hypoglycemia as well as hyperbilirubinemia requiring phototherapy.
The mother reported normal prenatal care and unremarkable ultrasound as well as negative group B Streptococcus status. Aside from prematurity, the patient had no risk factors for neonatal hypoglycemia nor any risk factors for infection such as maternal preterm premature rupture of membranes (PPROM) or intrapartum fever. She did not have a lumbar mass noted at NICU admission, nor did she undergo a lumbar puncture. Since discharge, her past medical history consisted of clinically diagnosed gastroesophageal reflux disease (GERD) and mild nasal congestion 1 week prior. The patient had been breastfed, and her mother had been avoiding dairy and soy because of infant reflux.
On physical exam, the patient was well appearing, lying comfortably in her mother’s arms. Her temperature was 98.78°F; heart rate was 141 beats per minute; blood pressure was 90/53 mm Hg; and respiratory rate was 42 breaths per minute. Her head was normocephalic and atraumatic with soft anterior fontanelle. Her skin was warm, dry, and pink, with a 3.5-cm diameter erythematous indurated raised area with fluctuance superior to the gluteal cleft at the base of the lumbar spine (Figure 1). The area seemed tender to the touch and was without spontaneous drainage. She had no dimples or sacral tuft. She had no rashes. Her abdomen was soft and nondistended without organomegaly. Her anus was patent. The child was otherwise well developed with normal tone and was moving all extremities. She had normal primitive reflexes.
Complete blood count was remarkable for a normal white blood cell count of 12.81 thousands per microliter (K/μL; normal range [NR], 7.00-17.00 K/μL); hemoglobin, 13.0 g/dL (NR, 11.0-17.4 g/dL); hematocrit, 38.3% (NR, 34.0%-52.0%); and elevated platelets, 410 K/μL (NR, 150-350 K/μL). Her basic metabolic panel was within normal limits, as was her C-reactive protein (0.3 mg/dL [NR, 0-0.5 mg/dL]). Erythrocyte sedimentation rate was elevated at 44 mm/h. A peripheral blood culture was obtained, but urine studies were not pursued. Cerebrospinal fluid studies were not obtained because of cellulitis overlying the lumbar spine.
Differential diagnosis upon initial evaluation included infectious, structural, and neoplastic etiologies (Table). Infectious concerns of a sacral mass include pilonidal cyst or another infection confluent with the spinal cord. Pilonidal cyst most commonly affects adult men but the possibility remains in infants.1
Structural concerns are especially pertinent in neonates and infants, although many of these abnormalities are detected in utero. Myelomeningocele is a defect of the dorsal arch leading to external exposure of the meninges and spinal cord. This defect may be an open lesion or may be covered by skin and can best be evaluated by magnetic resonance imaging (MRI). Myelomeningocele may be associated with a neurologic deficit in which the manifestation depends on the level of the lesion, and it may occur in isolation or in association with a genetic syndrome. A meningocele is less common and involves herniation of only the meninges without any neural elements.2,3
Spina bifida occulta involves a defect in the vertebrae without any protrusion of the spinal cord and may be associated with minor abnormalities of the skin including nevus, dermal sinus or dimple, hemangioma, or hirsute area.
Finally, spinal lipoma is fat within the spinal cord related to abnormal migration of mesodermal cells that may present as a midline mass and is associated with symptoms related to spinal cord compression or tethered cord.4
Neoplasms such as sacrococcygeal teratoma can occur early in life and may be detected prenatally, as they are associated with fetal hydrops and hydramnios.3 This abnormality is the most common extragonadal germ cell tumor and is usually benign. It may be asymptomatic, associated with rectal or bladder obstruction, or, rarely, with weakness and paralysis.5
Neuroblastoma is a malignancy of neural crest tissue arising from sympathetic ganglia. It may present as a firm, fixed, irregularly shaped mass lateral of midline, usually with poorly defined margins. It also can cause paralysis and bowel or bladder dysfunction related to paraspinous extension through spinal foramina.6