Thanks to Dr. Vasiliki Tzelepi, University of Patras, Patras (Greece) for contributing this case, Dr. Hillary Zalaznick, Myriad Genetics, Inc., Utah (USA) for editing the discussion and Kelly R. Magliocca, D.D.S., M.P.H., Emory University School of Medicine, Georgia (USA) for her review. To contribute a Case of the Week, first make sure that we are currently accepting cases, then follow the guidelines on our main Case of the Week page.
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A 69 year old woman presented to the ENT outpatient clinic with a small indurated lesion on the lateral border of her tongue, which was excised.
Which of the following is true of subgemmal neurogenous plaque?
The biopsy showed benign, nondysplastic squamous epithelium, with a spindle cell proliferation in the lamina propria. The lesion displayed a biphasic pattern (Fig. 1). The upper part of the lesion showed wavy spindle cells in a collagenous background, similar to a neurofibroma, with no evidence of atypia (Fig. 2). The lower part of the lesion showed disorganized nerve fascicles with ganglion cells in a neuroma-like pattern (Fig. 3). Immunohistochemically, both parts of the lesion showed intense S100 staining (Fig. 4). EMA was positive in the lower part of the lesion (Fig. 5). CK8/CK18 staining was negative in the lesion but highlighted the taste buds in the overlying epithelium (Figs. 6 and 7). These findings are consistent with a diagnosis of subgemmal neurogenous plaque.
Subgemmal neurogenous plaque (SNP, also called the subepithelial nerve plexus of taste buds) is a normal neural structure associated with taste buds, found on the posterior third of the lateral tongue. SNPs are generally asymptomatic but may present as white or red patches, hyperplastic nodules, ulcers or complaints of a burning sensation. As described for this case, they show a biphasic pattern; the superficial part of the lesion contains elongated and wavy spindle cells running in parallel to the epithelium and the deeper part contains small nerve fascicles and scattered ganglion cells. The superficial portion can contain varying amounts of collagen similar to a neurofibroma and also may have an inflammatory infiltrate and lymphoid follicles. The spindle cells in the superficial part of the lesion are positive for S100 and NSE. NSE also stains the ganglion cells in the deeper part of the lesion. Staining for CD56 is present throughout the lesion in a fibrillar pattern. EMA stains the nerve fascicle sheaths in the lower part of the lesion, and also the squamous epithelium above the lesion (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2009;108:920, Int J Oral Maxillofac Surg 2008;37:773).
SNPs can be found incidentally in head and neck resections involving the lateral tongue and are important to recognize for two main reasons. First, they can be confused for neural neoplasms such as neurofibroma or neuroma. Distinguishing SNPs from other neural lesions is typically straightforward because of their biphasic pattern, association with taste buds, and localization to the posterior lateral tongue (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2009;108:920). The second reason for recognizing SNPs is that cytologically bland islands of squamous cells have been reported within or near SNPs (not seen in the current case); these squamous islands are thought to be embryologic remnants and should not be confused with invasive squamous cell carcinoma involving neural structures (Oral Surg Oral Med Oral Pathol Oral Radiol 2014;117:497).
D. They are normal neural structures associated with taste buds.