Acral Cutaneous Intraneural Pseudoperineurioma.

Several cutaneous neurovascular stromal lesions are clinically and pathologically ill-defined entities. They are known by different nomenclatures, often unrecognized, misinterpreted, and confused with other skin lesions. Reports have documented cases of palmar and oral lesions in both children and adults. There is uncertainty regarding their true prevalence, clinicopathologic characteristics, and classification. Our aim is to highlight the salient histopathologic, histochemical, and immunohistochemical features of acral nodular tumors showing perineuriomatous differentiation. We found 3 teenagers (0.2%) [2 females, 1 male, average age: 13 years] with hand nodules out of 1331 patients with cutaneous and oral polypoid lesions. They were isolated, asymptomatic, nontraumatic, subcentimetric, palmar, digital nodules with an average duration of 5 years. They demonstrated dermal-based anomalous growths composed of thick tortuous neurovascular bundles and collagenous fibrovascular stroma. Masson trichome demarcated micronodular and plexiform neurovascular bundles showing concentric onion-bulb whorls ensheathed in collagenous fibrovascular stroma. Elastic fibers were absent. Alcian blue demonstrated intraneural mucinous alteration and loose interstitial myxoid mesenchyme. CD31, ERG, and smooth muscle actin highlighted small intraneural capillary-sized, and larger venous and arteriolar interstitial vasculatures. CD34 decorated the interstitial mesenchyme. S100, SOX10, and neurofilament revealed sparse neural components, whereas EMA and GLUT1 highlighted prominent perineurial components within the neurovascular bundles and onion-bulb micronodules. The findings suggest that cutaneous intraneural pseudoperineurioma nodules may represent a distinct clinicopathologic entity among traumatic neuromas, resembling cutaneous intraneural perineurioma. Further validation studies are necessary because of the small size of the case series and the lack of molecular genetic studies.