Lymphoma: This is a common cause of both lymph node enlargement and infiltration of the fat in the abdominal wall, particularly if the lymphoma is of a type that tends to involve the abdominal cavity, such as diffuse large B-cell lymphoma.

Metastatic Cancer: Cancers from various primary sites (e.g., breast, lung, melanoma) can metastasize to the abdominal lymph nodes and infiltrate the fat of the abdominal wall.
Sarcoma: Although less common, sarcomas (e.g., liposarcoma) can arise in the fat of the abdominal wall and cause lymph node enlargement due to metastasis.
Inflammatory or Infectious Processes: Conditions like tuberculosis or fungal infections can cause both lymphadenopathy and infiltration of the abdominal wall fat, especially in immunocompromised patients.

Desmoid Tumor (Aggressive Fibromatosis): Although rare, desmoid tumors can infiltrate the abdominal wall and cause significant morbidity. They are often associated with Gardner syndrome or familial adenomatous polyposis (FAP).
Retroperitoneal Fibrosis: This condition can cause infiltration of the retroperitoneal fat and lymph node enlargement, and it's crucial to diagnose it early to prevent complications like ureteral obstruction.

Castleman Disease: A rare lymphoproliferative disorder that can cause lymph node enlargement and systemic symptoms, and in some cases, may involve the abdominal wall.
** Erdheim-Chester Disease**: A rare form of histiocytosis that can cause infiltration of various tissues, including the abdominal wall fat, and is associated with lymphadenopathy and systemic symptoms.
Whipple Disease: A rare bacterial infection that can cause malabsorption, weight loss, and lymphadenopathy, including involvement of the abdominal lymph nodes and fat.