Hepatosplenic T-cell Lymphoma : Morphology
Gross Morphology: The spleen is massively enlarged weighing between 1000 and 3500 grams. It has a homogenous red-purple cut surface free of lesions. There is no hilar lymphadenopathy.
Microscopic Features: SPLEEN: There is red pulp expansion due to diffuse infiltration of the cords and sinuses by the neoplastic cells with preservation of architecture. White pulp areas are reduced or completely lost. The red pulp is infiltrated by medium-sized, monomorphic lymphoid cells with pale cytoplasm and round to oval or slightly irregular nuclei containing inconspicuous nucleoli. Mitotic activity and pleomorphism are not prominent. Other cells types that are present include numerous histiocytes, few small lymphocytes, and rare plasma cells. The hilar lymph nodes are not enlarged but may still show involvement of sinuses or perisinusoidal areas. The nodal architecture is preserved.
LIVER: Liver involvement leads to hepatomegaly in most cases. The neoplastic infiltrate is present predominantly in the sinusoids. There may be a minor component of portal or periportal lymphoid infiltrate.
BONE MARROW: Bone marrow is involved in most cases. The bone marrow biopsies are hypercellular with trilineage expansion and can resemble myelodysplastic or myeloproliferative syndrome. The neoplastic infiltrate consists of small to medium-sized atypical lymphoid cells in aggregates or single files expanding the bone marrow sinuses. The lymphoma cells may be inconspicuous on routine H&E stains but are highlighted by CD3 immunostain.
In bone marrow smears, there may be small population of blast-like cells, cells with hairy projections, or cells containing fine cytoplasmic granules. With disease progression, the bone marrow involvement becomes more diffuse and interstitial and the tumor spills over beyond the sinuses. The cells become larger with blast-like features.