What is characterized by abnormal growths that usually appear on a baby's neck or head consisting of fluid-filled sacs?

Cystic hygromas are indeed characterized by abnormal growths typically found on a baby's neck or head, appearing as fluid-filled sacs. These lesions result from a malformation of the lymphatic system, where lymphatic fluid accumulates in poorly formed lymphatic vessels. They are often noticed at birth or shortly thereafter and can vary in size. The presence of cystic hygromas can be associated with certain congenital syndromes and may require monitoring or surgical intervention depending on their size and the symptoms they may cause.

In contrast, hemangiomas are benign tumors consisting of blood vessels that commonly appear on a baby's skin, often manifesting shortly after birth. Neurofibromas are nerve sheath tumors that typically do not present until later in life and are associated with neurofibromatosis. Fibromas are benign fibrous tumors that are not typically associated with the lymphatic system or fluid accumulation in newborns. Each of these other conditions presents differently and is associated with distinct characteristics, making cystic hygromas unique in their presentation as fluid-filled sacs on the neck or head.