10-year-old with right upper arm mass measuring 1.5 cm

Pediatric Pathology

Authors

Harini Venkatraman Ravisankar, MBBS
Erin Rudzinski, MD

Summary of clinical history
A 10-year-old male patient noticed a small mass on his right upper arm two years ago. Over time, the mass increased in size to approximately 1.5 cm and became tender to touch. Surgical excision of the mass was performed.

Gross findings
The specimen consisted of fragmented, tan-yellow, firm, lobulated fibroadipose tissue, measuring a total of 2.4 × 2.1 × 0.6 cm. One of the fragments included an attached ellipse of skin.

Microscopic findings

• Spindled to epithelioid cells arranged in whorls and fascicles against a myxoid background
• The cells are present in the dermis
• Dense bundles of collagen separate the cells into nodules
• Variable nuclear atypia

Click any image for larger version.

Figure 1: H&E, 40x- Dermal nodule with lobulated nests of spindle-to-epithelioid cells separated by dense collagen

Figure 2: H&E, 100x- Individual cells are spindle-to-epithelioid against a myxoid stroma

Immunohistochemical findings

• Positive stains: PGP9.5 and MiTF (subset)
• Negative stains: S100, GFAP and Melan A

Figure 3: IHC, 100X- The cells are highlighted by PGP9.5 immunohistochemical stain

Figure 4: IHC, 100X- A subset of the cells highlighted by MiTF immunohistochemical stain

Clinical Presentation

• Neurothekeomas typically present as solitary dermal or subcutaneous nodules

• They are usually less than 2 cm, and arise on the head, neck, or upper extremities of young adults.

• Presentation is often described as a painless, slow-growing, skin-colored to pink papule or nodule

Histology

• Lesions are well-circumscribed, non-encapsulated dermal tumors with lobulated nests or fascicles of spindle-to-epithelioid cells in a variably myxoid/collagenous stroma.

• Histologic variants include myxoid (>50% myxoid stroma), cellular (≤10 myxoid stroma), and mixed types.

• Cellular neurothekeoma frequently exhibits a nested/fascicular pattern, occasional cytologic atypia, low-to-moderate mitotic rates and rare perineural or vascular invasion — but overall, they do not result in distant metastasis or death from disease.

Immunohistochemical findings

• Positive stains: Vimentin, NKI / C3, CD10, PGP9.5 and MiTF

• Negative stains: S100, GFAP, MelanA, EMA, CD34, Desmin, CK

Key differential diagnosis

• Neural tumors (myxoid schwannoma, neurofibroma, dermal nerve sheath myxoma)
  Positive stains: S100, Sox10

• Plexiform histiocytic tumor
  Positive stains: CD68, CD163, Lysozyme, Factor XIIIa, Vimentin
  Negative stains: S-100, GFAP, Cytokeratins, EMA, Melanocytic markers: HMB-45, Melan-A, MITF, CD34

References

• Stratton, J., & Billings, S. D. (2014). Cellular neurothekeoma: analysis of 37 cases emphasizing atypical histologic features. Modern Pathology, 27(5), 701-710.

• Park, M. C., & Seung, W. B. (2016). Cellular Neurothekeoma of the Scalp in the Elderly. Brain Tumor Research and Treatment, 4(1), 17.

• Yun, S. J., Park, H. S., Lee, J. B., Kim, S. J., Lee, S. C., & Won, Y. H. (2014). Myxoid cellular neurothekeoma: a new entity of S100-negative, CD68-positive myxoid neurothekeoma. Annals of dermatology, 26(4), 510.

• Papadopoulos, E. J., Cohen, P. R., & Hebert, A. A. (2004). Neurothekeoma: report of a case in an infant and review of the literature. Journal of the American Academy of Dermatology, 50(1), 129-134.

• Sperling, L. C., Hardy, C. L., & Love, T. V. (2022). Atypical cellular neurothekeoma: a lamb in wolf’s clothing. JAAD Case Reports, 30, 111-113.