Congenital mesoblastic nephroma (CMN) is the most common renal tumor of early infancy, and infants with renal masses suspicious for CMN often undergo upfront radical nephrectomy with proximal ureterectomy. Infective mimics, including renal abscess, acute lobar nephronia, and xanthogranulomatous pyelonephritis, are considerably less common, particularly when typical clinical signs of infection are absent or muted. We report the case of a 2-month-old boy with a painless, progressively enlarging left abdominal mass first noted at 20 days of age, accompanied by intermittent low-grade fever and constipation. Contrast-enhanced computed tomography showed an ill-defined, heterogeneously enhancing left renal mass with perinephric extension and regional lymphadenopathy, raising suspicion for CMN. The infant underwent radical left nephroureterectomy with splenic flexure resection, the latter of which was required because of dense inflammatory adhesions. Histopathological examination revealed a chronic suppurative renal abscess with palisading histiocytes and multinucleated giant cells, with no evidence of malignancy, fungal organisms, or mycobacteria. Postoperative recovery was uneventful, and the child remains well during follow-up. This case illustrates a rare but clinically important diagnostic pitfall: infective renal masses can masquerade as malignant renal tumors in early infancy, particularly when systemic inflammatory features are subtle.

Internal hernia is an uncommon cause of small bowel obstruction, especially in children and adolescents with no history of abdominal surgery. Among its subtypes, transmesenteric hernia through a mesenteric defect is rare but clinically important because it can lead to closed-loop obstruction, bowel ischemia, and intestinal strangulation. Early diagnosis and timely surgical treatment are therefore essential. A previously healthy 15-year-old boy was transferred to our emergency department with left upper quadrant abdominal pain and vomiting that had persisted for 2 days. His vital signs were stable on arrival, and physical examination showed only mild left upper quadrant tenderness, with no abdominal distension. Abdominal computed tomography revealed two transition points in the mid-abdomen and dilatation of the left-sided small bowel loops, findings suggestive of closed-loop obstruction. Emergency laparoscopic exploration showed two segments of small bowel herniated through a defect in the jejunal mesentery. Although laparoscopic reduction was attempted first, marked bowel dilatation and the small size of the mesenteric defect prevented safe reduction. The procedure was therefore converted to open surgery through a periumbilical incision. The incarcerated bowel loops were carefully reduced, and the mesenteric defect was closed with interrupted sutures. The patient developed mild postoperative ileus, which resolved with conservative treatment. At the 1-year follow-up, he remained well, with no recurrence or postoperative sequelae. Transmesenteric internal hernia caused by a mesenteric defect should be considered in adolescents with small bowel obstruction, even when they have no history of abdominal surgery. Prompt surgical exploration and closure of the mesenteric defect may prevent bowel ischemia and strangulation and support favorable outcomes.

Rectal polyps are relatively common in children and most often present as painless rectal bleeding after defecation. By contrast, rectal prolapse caused by an underlying rectal polyp is uncommon, especially in pediatric patients. Because intermittent prolapse may have resolved by the time of clinical examination, the diagnosis can be difficult to establish. A previously healthy 1-year-old boy was referred to the pediatric surgery outpatient clinic because of a 6-month history of intermittent protrusion of a mass through the anus after defecation. The episodes initially occurred approximately three times per day but gradually increased to six times per day. Physical examination showed no definite perianal abnormality; however, a photograph provided by the patient’s mother showed a protruding anorectal mass, raising suspicion for rectal prolapse associated with a polyp. Colonoscopy revealed a large pedunculated rectal polyp, measuring approximately 47×34×25 mm, with a short stalk located approximately 15 cm proximal to the anal verge. The patient underwent transanal excision under general anesthesia. Histopathological examination confirmed a Peutz-Jeghers-type hamartomatous polyp. The postoperative course was uneventful, and no recurrence was observed during 3 years of follow-up. Rectal polyps should be considered in the differential diagnosis of recurrent rectal prolapse in infants and young children. Caregiver-provided photographs can help establish the diagnosis when the lesion is not visible during examination. In selected pediatric patients with large rectal hamartomatous polyps presenting with recurrent prolapse, transanal excision may provide safe and effective treatment.

Undifferentiated embryonal sarcoma of the liver (UESL) is a rare and highly aggressive malignant mesenchymal neoplasm that occurs mainly in school-aged children. Preoperative diagnosis is challenging because clinical symptoms are nonspecific and imaging findings can vary substantially. Despite these diagnostic difficulties, survival has improved markedly with modern multimodal treatment. A previously healthy 10-year-old girl presented with acute right upper quadrant abdominal pain. Laboratory findings were largely unremarkable, and the alpha-fetoprotein level was within the normal range. Contrast-enhanced abdominal computed tomography and magnetic resonance imaging showed a large heterogeneous cystic mass in the right hepatic lobe, with internal hemorrhage, hemorrhage-fluid levels, and enhancing solid components. Right hepatectomy was performed, and complete tumor resection was achieved. Histopathological evaluation revealed a high-grade malignant mesenchymal tumor with pathological and immunohistochemical features consistent with UESL. The patient subsequently received adjuvant chemotherapy. At 21 months after surgery, she remained disease-free, with no radiological or clinical evidence of recurrence. This case highlights the diagnostic value of characteristic imaging findings and the therapeutic importance of complete resection followed by adjuvant chemotherapy. Early recognition and coordinated multidisciplinary management are essential for improving prognosis in children with this rare hepatic malignancy.