Benign mesenchymal lymph node tumor characterized by palisading spindle cells, stellate deposits of collagen (amianthoid fibers), and hemorrhage.

Intranodal hemorrhagic spindle cell tumor with amianthoid fibers.

Because cells derived from smooth muscle usually contain desmin, the absence of desmin in palisaded myofibroblastoma (PM) initially suggested a cell type other than smooth muscle (1,2). Intracytoplasmic inclusions, similar to those seen in infantile digital fibroma (an accepted myofibroblastic tumor), seemed to support a myofibroblastic origin. On the other hand, vascular or capsular smooth muscle cells could also give rise to the spindle cells of PM (1,2,3,4). A variety of immunohistochemical and ultrastructural features are compatible with either myofibroblasts or smooth muscle cells (2).

Most patients with PM have a solitary, unilateral, painless nodular mass confined to the inguinal area (1,2,5). Rarely, PM occupies cervical (5) or submandibular lymph nodes (6,7). In three series, patients’ ages ranged from 19 to 67 years, and more men than women were affected (1,2,5). Many PMs develop in the sixth decade (2,5). The behavior of PM is completely benign. A single inguinal case recurred locally after 9 years (8).

Palisaded myofibroblastomas are well encapsulated and located deep in the groin below the inguinal ligament, do not infiltrate overlying skin, and involve no more than a single lymph node. They measure 0.6 to 5 cm in diameter. Sectioning the lymph node reveals a gray-white tumor surrounded by focal areas of subcapsular hemorrhage (1), like “milk freshly poured into tea” (5).

The tumor mass has a nodular configuration and is composed of crisscrossed fascicles of parallel, slender, spindle-shaped cells (Fig. 82.1). The cytoplasm is weakly eosinophilic without striations, and the nuclei are tapered and often aligned, displaying palisading patterns. Nuclear atypia is absent, and mitoses are rare, usually fewer than two per 50 high-power fields. A characteristic feature observed in all cases is the presence of mats of eosinophilic material forming bands of stellate or circular profiles, depending on the plane of section (1,2,5) (Figs. 82.1 and 82.2). These are composed of a core of homogeneous, deeply eosinophilic collagen with fine hair-like spokes surrounded by a peripheral, granular, weakly eosinophilic area (1). The collagen stains intensely blue with trichrome stain (Figs. 82.3 and 82.4). The general appearance is that of amianthoid fibers, previously described in some malignant mesenchymal schwannomas and considered to represent degenerated or “crystalline” collagen (9,10). The tumor is surrounded by a pseudocapsule composed of thick bands of hyalinized sclerotic tissue that separate it from the compressed peripheral lymphoid tissues of the lymph node. In some areas, small vessels lined by flat endothelial cells and containing erythrocytes are at the center of the amianthoid structures, suggesting perivascular rosettes (2). Zones with scattered hemorrhagic foci can resemble Kaposi sarcoma.