Introduction: Lymphangiomas are rare congenital malformations, which affect lymphatic vessels, and sometimes blood vessels, which is known as hemolymphangioma (1,2). They are benign tumors, however, they can infiltrate into adjacent tissues and relapse (3,4) or can compress adjacent organs due to their rapid growth.

Two pathogeneses have been suggested:

• One hypothesizes an alteration of the embryonic development of lymphatic vessels, which begin forming at about 6 weeks.
• The second considers an altered development of the communication between lymphatic and blood vessels (5).

Lymphangiomas are classified into three groups: simple, complex and cystic, known as hygroma ( 6,7 ). They can be found in every part of body where lymphatic vessels are present. In 95% of cases, they are concentrated in the region of head, axillary fossa, neck, and less frequently in the small intestine.

In ultrasound, lymphangiomas appear as a polycystic mass with variable sizes. There can be one or multiple septa with thin walls. Solid neoplastic components present with low resistance flow under Color Power Doppler (8). Generally, there are no chromosomal abnormalities, however, hydrops, polyhydramnios and skin edema are frequent findings (6,9). Prognosis is better if edema is not present (10).

After birth, therapy depends on size and site of lesion. Surgery can be performed on large neoplasms, however, there is an association with high morbidity and mortality rate (11). Relapses occur in about 30 — 40% of cases. Ultrasound plays a very important role in early diagnosis of this kind of lesion.

Case report: A 31-year-old patient at 25 gestational weeks had suspected fetal abdominal mass. It was her 3^rd pregnancy with a previous abortion and one molar pregnancy.
The male fetus, with normal growth curve, had normal skull, brain, heart, limbs, spine, kidneys, stomach, placenta, and amniotic fluid indexes (Figure 1, 7).
The following findings were present: a polycystic mass in the fetal abdomen, measuring 100mm x 65 mm, with no evidence of blood flow (Figure 2, 3, 4, 5, 6, 8). The suspected diagnosis was "Abdominal Lymphangioma".
A follow up ultrasound was performed. The situation remained unchanged: normal fetal growth with no sign of cardiac failure or ascites. At 31 gestational weeks,  polyhydramnios developed and then a premature rupture of the membrane occurred resulting in a delivery by Cesarean Section.
Due to the appearance of ascites, the baby underwent a partial resection operation after 24 hours and again in 8 days. The operations were successful and he is in good clinical condition.
Histologic examination of the mass confirmed the early diagnosis of "cystic mesenteric lymphangioma".