Vascular transformation of sinuses in lymph nodes. A study of its morphological spectrum and distinction from Kaposi's sarcoma.

Vascular transformation of lymph node sinuses (VTS) is characterized by conversion of nodal sinuses into capillary-like channels, often accompanied by fibrosis. A detailed study of this entity, based on 76 cases, showed that the morphologic spectrum was much broader than that originally described. The vasoproliferative process caused variable expansion of the subcapsular, intermediate, and medullary sinuses of the lymph nodes and involved single or multiple lymph nodes in a diffuse or segmental fashion. The proliferated vessels formed anastomosing narrow clefts, rounded spaces of different sizes, plexiform channels, or solid spindled to plump cellular foci and often were associated with variable degrees of sclerosis. The vascular spaces were empty, filled with lymph-like fluid, congested with blood, or occasionally thrombosed; extravasation of red cells was common. Several patterns were commonly observed in an individual case. Less common features included perivascular fibrin deposition and the presence of eosinophilic globules. Vascular thrombosis was identified only rarely in extranodal vessels available for histologic assessment. The more cellular forms of this vascular transformation may be mistaken for Kaposi's sarcoma, but can be distinguished from it by the pure sinusoidal distribution, a lack of well-formed spindle cell fascicles, the associated fibrosis, the maturation of the spindle cells into well-formed vascular channels toward the capsular aspect, and the failure of this process to involve the capsule itself, which is frequently affected by Kaposi's sarcoma.