Question: How is primary intestinal lymphangiectasia (PIL) caused?

Context:
Primary intestinal lymphangiectasia (PIL) is a rare disorder of unknown etiology characterized by diffuse or localized dilation and eventual rupture of the enteric lymphatic vessels in mucosa, submucosa, and/or subserosa. Lymph, rich in all kinds of proteins and lymphocytes, leaks into the gastrointestinal tract via the affected lymphatic vessels causing hypoproteinemia and lymphopenia. 
PIL, effusions, and lymphedema can be the features of multisegmental generalized lymphatic dysplasia.
A number of disorders have been described to cause protein losing enteropathy (PLE) in children. Primary intestinal lymphangiectasia (PIL) is one mechanism leading to PLE.
Primary intestinal lymphangiectasia is a rare cause of protein-losing enteropathy and usually presents with intermittent diarrhea or malnutrition. Diagnosis depends largely on its pathologic condition demonstrating greatly dilated lymphatics mainly in the lamina propria of the mucosa. 
The histopathologic condition of the resected small intestine showed lymphatic dilation limited mainly to the subserosa and mesentery but was not prominent in the mucosa.
Primary intestinal lymphangiectasia (PIL) is a rare disorder characterized by dilated intestinal lymphatics and the development of protein-losing enteropathy.
Primary intestinal lymphangiectasia (PIL), also known as Waldmann's disease, is an exudative enteropathy resulting from morphologic abnormalities in the intestinal lymphatics.
Primary intestinal lymphangiectasia (PIL), so-called Waldmann's disease, is an uncommon condition, characterized by dilated intestinal submucosal and subserosal lymphatics of the gastrointestinal tract.
Primary intestinal lymphangiectasia (PIL) is a rare disorder characterized by dilated intestinal lacteals resulting in lymph leakage into the small bowel lumen and responsible for protein-losing enteropathy leading to lymphopenia, hypoalbuminemia and hypogammaglobulinemia.
Primary intestinal lymphangiectasia (PIL), also known as Waldmann's disease, is a rare disorder characterized by dilated intestinal lacteals resulting in lymph leakage into the small bowel lumen and responsible for protein-losing enteropathy leading to lymphopenia, hypoalbuminemia and hypogammaglobulinemia.
Primary intestinal lymphangiectasia (PIL) is a protein-losing, exsudative gastroenteropathy causing lymphatic obstruction.
Primary intestinal lymphangiectasia (PIL) is a protein-losing enteropathy characterized by tortuous and dilated lymph channels of the small bowel.
Primary intestinal lymphangiectasia (PIL) is a rare disease of intestinal lymphatics presenting with hypoproteinemia, bilateral lower limb edema, ascites, and protein losing enteropathy.
Exudative enteropathy secondary to primary intestinal lymphangiectasia (PIL) is characterized by lymphopenia, hypogammaglobulinemia and hypoalbuminemia resulting from leakage of lymph fluid into the intestinal tract
Primary intestinal lymphangiectasia (PIL) is a rare protein-losing enteropathy with lymphatic leakage into the small intestine
Primary intestinal lymphangiectasia (PIL) is a protein-losing enteropathy characterized by tortuous and dilated lymph channels of the small bowel
Primary intestinal lymphangiectasia (PIL) is a rare disease of intestinal lymphatics presenting with hypoproteinemia, bilateral lower limb edema, ascites, and protein losing enteropathy
Primary intestinal lymphangiectasia (PIL), so-called Waldmanns disease, is an uncommon condition, characterized by dilated intestinal submucosal and subserosal lymphatics of the gastrointestinal tract
Primary intestinal lymphangiectasia (Waldmanns disease) is a rare disease characterized by dilated lymphatics in the small bowel leading to an exudative enteropathy with lymphopenia, hypoalbuminemia and hypogammaglobulinemia.We report the case of a 23 year-old male who presented with chronic anemia and in whom primary intestinal lymphangiectasia was diagnosed
We report a series of 4 children from Chennai, India presenting with anasarca, recurrent diarrhea, hypoproteinemia and confirmatory features of PIL on endoscopy and histopathology.
Primary intestinal lymphangiectasia (PIL) is a protein-losing, exsudative gastroenteropathy causing lymphatic obstruction. 
Primary intestinal lymphangiectasia (PIL) is a rare protein-losing enteropathy characterized by a congenital malformation of the lymphatic vessels of the small intestine causing insufficient drainage and leakage of lymph fluid.
Primary intestinal lymphangiectasia (PIL) is a rare protein-losing enteropathy with lymphatic leakage into the small intestine.
Primary intestinal lymphangiectasia (PIL) or Waldmann's disease is a rare protein-losing gastroenteropathy of unknown etiology.

Answer: Primary intestinal lymphangiectasia (PIL) is a rare disorder characterized by diffuse or localized dilation and eventual rupture of the enteric lymphatic vessels in mucosa, submucosa, and/or subserosa. Lymph, rich in all kinds of proteins and lymphocytes, leaks into the gastrointestinal tract via the affected lymphatic vessels causing hypoproteinemia and lymphopenia.