A Giant Pediatric Chylolymphatic Cyst: An Extremely Rare Entity

**Background:** Mesenteric cysts are rare, and chylolymphatic cysts—a variant containing both chyle and lymph—are even rarer, with a prevalence of 1 per 20,000 children. Most literature addresses adult cases, and pediatric data are sparse. These cysts are thought to arise from isolated or ectopic lymphatic channels in the small bowel mesentery due to an imbalance between fluid inflow and outflow. Diagnosis by age 10 years occurs in 25% of cases. Clinical and radiological features are non-specific, making preoperative diagnosis difficult.

**Methods:** This is a single case report of a 2-year-old female child who presented with 3 days of abdominal pain and two episodes of nonbilious vomiting. Examination revealed a vague, firm, ill-defined mass below the umbilicus. Ultrasonography showed a multicystic intra-abdominal lesion. PET-CT revealed a large ill-defined infiltrative mass (16 × 13.2 × 6.7 cm) centered in the mesocolonic fat, involving the umbilical, infraumbilical, and hypogastric regions with extension into both iliac fossae, without significant contrast enhancement. A provisional diagnosis of mesenteric cyst was made. Laparotomy revealed multiple lymphatic cysts of variable sizes arising from the mesentery of the proximal ileum (25 cm proximal to the ileocecal junction), closely related to the intestine and extending to the root of the mesentery. Approximately 25 cm of ileum was resected en bloc with the mass, followed by anastomosis.

**Key Results:** Gross examination showed a large multicystic mass measuring 17 × 10 × 4 cm. Serial sectioning revealed milky white fluid. Microscopy demonstrated variable-sized, anastomosing, ill-defined cystic spaces with thin walls lined by flattened endothelial cells, filled with foamy histiocytes and proteinaceous fluid. Immunohistochemistry showed D2-40 positivity in the lymphatic endothelial lining, confirming the diagnosis of chylolymphatic cyst. The patient was doing well at 6-month follow-up with no evidence of recurrence. A literature review identified only 12 articles (17 patients) on pediatric chylolymphatic cysts. Among these, only two cases (including the present one) qualified as giant chylolymphatic cysts (>15 cm). The most common presenting symptoms across reviewed cases were abdominal pain and distension; other symptoms included vomiting, constipation, acute intestinal obstruction, severe back pain, and scrotal swelling. No recurrence was reported in any case with follow-up.

**Clinical Implications:** Chylolymphatic cysts should be considered in the differential diagnosis of pediatric abdominal cystic masses, especially when imaging shows a large, multicystic, non-enhancing mesenteric lesion. Surgical excision with or without bowel resection is the mainstay of treatment. Histopathology with D2-40 immunohistochemistry is essential for definitive diagnosis and to exclude differentials such as cystic lymphangioma, multilocular peritoneal inclusion cyst, and lymphoepithelial cysts. The prognosis after complete excision appears excellent, with no reported recurrences in the literature.