Viral infection: A borderline enlarged spleen can often be seen in the context of a viral infection such as mononucleosis (infectious mononucleosis caused by Epstein-Barr virus) due to the spleen's role in filtering the blood and storing lymphocytes.

Chronic liver disease: Conditions like cirrhosis can lead to portal hypertension, causing the spleen to become enlarged (splenomegaly) due to increased pressure in the portal vein system.
Lymphoma: Both Hodgkin's and non-Hodgkin's lymphoma can cause splenomegaly as the disease progresses and involves the spleen.
Chronic infections: Certain chronic infections such as endocarditis or tuberculosis can also lead to a borderline enlarged spleen.

Sickle cell disease: While more commonly associated with a small, fibrotic spleen in later stages, early stages or specific variants of sickle cell disease can present with splenomegaly.
Lymphatic leukemia: Leukemias, especially chronic lymphocytic leukemia (CLL), can cause significant splenomegaly.
Portal vein thrombosis: This condition can lead to splenomegaly due to increased pressure in the spleen and is critical to diagnose due to its potential for severe complications.

Gaucher's disease: A genetic disorder leading to the accumulation of glucocerebroside in cells, which can cause splenomegaly among other symptoms.
Amyloidosis: The deposition of amyloid proteins in the spleen can lead to its enlargement.
Sarcoidosis: Although more commonly associated with lung and lymph node involvement, sarcoidosis can rarely cause splenomegaly.
Histiocytosis: Certain types of histiocytosis, like Langerhans cell histiocytosis, can involve the spleen and cause enlargement.