Ultrastructural study of nuclear inclusions in spindle and epithelioid cell nevus cells

Abstract

The nuclei of spindle and epithelioid cell nevus (SECN) cells often contain inclusions. To determine the origin and pathogenesis of the nuclear inclusions, 12 cases of SECN were electron microscopically examined. True inclusions, pseudoinclusions, and electron-lucent areas were frequently found in the nuclei of SECN cells in all cases. The true inclusions were composed of various structures including vesicles and electron-dense homogenous substance. The pseudoinclusions were a cytoplasmic structure engulfed by nucleus; they were surrounded by a nuclear membrane and rich in cytoplasmic vesicles and electron-dense materials. Occasionally, a partial dissolution of the covering membrane of the pseudoinclusions was seen, leaving their contents in the nuclear matrix. It was concluded that a sequential process from the pseudoinclusions to the true inclusions in nuclei was morphologically present in SECN cells.

True intranuclear inclusions in a melanocytic nevus: report of a case and review of the literature

“…Melanocytic neoplasms commonly show pseudo‐inclusions in melanocytic nuclei, on both histology and electron microscopy 14,15 . These pseudo‐inclusions appear to be in the nuclei, but contain cytoplasmic components, and are demarcated from the nuclear matrix by a nuclear membrane 15 …”

“…The authors suggested that the presence of pigmented organelles within the intranuclear inclusions was compatible with the hypothesis that these inclusions may have arisen for nuclear pseudo‐inclusions following the breakdown of the nuclear membrane or trapping of cytoplasmic constituents within the nucleus during atypical mitosis 18 . Sakamoto et al 15 identified true nuclear inclusions in spindle and epithelioid cell nevi (Spitz nevi) by electron microscopy. These inclusions varied in size (up to 2.4 μm in diameter), shape (i.e.…”

“…solid to doughnut) and structure (i.e. from concentrically arranged or randomly distributed fibrils to fibrillo‐granular structures, with electron‐dense matrices, vesicles and/or tubules) 15 . The authors did not submit their cases for routine histology, but postulated that nuclear pseudo‐inclusions may be one source of these true inclusions, secondary to the dissolution of the pseudo‐inclusion membrane, with subsequent fusion of intranuclear deposits to form larger inclusions 15 .…”

“…13 Melanocytic neoplasms commonly show pseudoinclusions in melanocytic nuclei, on both histology and electron microscopy. 14,15 These pseudo-inclusions appear to be in the nuclei, but contain cytoplasmic components, and are demarcated from the nuclear matrix by a nuclear membrane. 15 In contrast, true intranuclear inclusions/bodies have been rarely reported in melanocytes of normal skin, 2 in epidermal melanocytes following psoralenultraviolet A (PUVA) therapy 16 and in melanocytic tumors.…”

“…14,15 These pseudo-inclusions appear to be in the nuclei, but contain cytoplasmic components, and are demarcated from the nuclear matrix by a nuclear membrane. 15 In contrast, true intranuclear inclusions/bodies have been rarely reported in melanocytes of normal skin, 2 in epidermal melanocytes following psoralenultraviolet A (PUVA) therapy 16 and in melanocytic tumors. 15,[17][18][19][20][21][22][23] These true nuclear inclusions are present within the nuclear matrix and lack a border membrane.…”