Plexiform Melanocytic Schwannoma: Report of a Second Case and Overview of a Rare Entity
Bibliographic record
Abstract
ABSTRACT: The seminal case report of plexiform melanocytic schwannoma, published a decade ago, indicated that this is a rare variant of schwannoma demonstrating immunohistochemical expression of melanocytic markers, electron microscopic evidence of melanosome formation, and genetic features of a benign schwannoma. We report herein, a second example of this entity. Of added interest, our case showed pseudoglandular features, as previously recorded in other variants of schwannoma. A 66-year-old man presented with a cutaneous papule on the abdomen. Histopathologically, a vertically oriented, exoendophytic, folliculocentric, dermal tumor with a plexiform architecture was observed. This was composed of nodules and diverging fascicles of bland spindle-shaped cells. Notable interstitial mucin deposition conveyed a pseudoglandular appearance to the lesion. The spindled cells co-expressed S100, SOX10, and HMB45. A minority of cells expressed Melan-A and MiTF. EMA and claudin-1 stained capsular and perifascicular perineurial cells. Melanin was absent. Plexiform melanocytic schwannoma represents one of several nerve sheath tumors that peculiarly display evidence of melanocytic differentiation. These include melanocytoneuroma, pigmented neurofibroma (or melanocytic neurofibroma), and malignant melanotic schwannian tumor. Of importance, these proliferations can be mistaken for melanocytic tumors, including melanoma. In expanding the literature on this topic, we discuss steps required to distinguish plexiform melanocytic schwannoma from melanoma and other nerve sheath tumors with melanocytic differentiation. The possible pathogenesis of these unusual neoplasms is also addressed.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".