Peritoneal Carcinomatosis: This is the most likely diagnosis due to the high prevalence of peritoneal thickening in patients with abdominal malignancies, particularly those with ovarian, gastric, or colorectal cancer. Peritoneal carcinomatosis is the spread of cancer throughout the surfaces of the peritoneal cavity, leading to thickening and potential symptoms such as abdominal pain and ascites.

Tuberculosis: Peritoneal tuberculosis can cause thickening of the peritoneum due to chronic inflammation and scarring. It's a common cause in endemic areas and should be considered, especially in patients with risk factors for tuberculosis.
Peritonitis: Bacterial or fungal peritonitis, whether spontaneous or related to dialysis, can lead to peritoneal thickening as a result of the inflammatory response.
Sclerosing Encapsulating Peritonitis: This condition involves a thick, fibrotic membrane encasing the intestines, often seen in patients on long-term peritoneal dialysis.

Mesothelioma: Although rare, peritoneal mesothelioma is a malignant condition that can cause peritoneal thickening. It's crucial to consider due to its poor prognosis and the need for early intervention.
Lymphoma: Both primary peritoneal lymphoma and secondary involvement from systemic lymphoma can cause peritoneal thickening. Missing this diagnosis could lead to delayed treatment of a potentially curable condition.

Desmoid Tumors: Also known as aggressive fibromatosis, these rare, benign tumors can cause peritoneal thickening and are often associated with Gardner syndrome or familial adenomatous polyposis.
Erdheim-Chester Disease: A rare form of histiocytosis that can involve the peritoneum, leading to thickening among other systemic manifestations.
Abdominal Cocoon Syndrome: A rare condition where a fibrotic cocoon encases the small bowel, potentially causing peritoneal thickening, more commonly seen in young females from tropical regions.