Cellular Neurothekeoma on the Lip.

Sir,

Neurothekeoma is a relatively rare benign tumor showing neural growing pattern. Usually neurothekeoma develops on the head and neck. Its occurrence on the lip is therefore rare. We herein describe a case of neurothekeoma on the lip of a woman.

A 35-year-old woman presented with a nodule on the lip that she first noted about 4 years ago. She had no significant medical history. Physical examination showed a 3.5 × 3.5 mm sized, red solid nodule on the left side of the upper lip [Figure 1]. Total excision of the nodule under local anesthesia was performed. Histopathological examination showed lobular tumor islands in the dermis. The border of nodules was clear. The nodules were composed of round-shaped large cells that had a low nucleo-cytoplasmic ratio and spindle-shaped nuclei [Figures 2a and b]. The surrounding myxoid matrices were positive for alcian blue staining. Results of immunohistochemistry showed that S-100 and microphthalmia-associated transcription factor (MITF) antigens were negative, whereas nerve growth factor (NGF) was positively stained in the tumor cells [Figure 2c]. Toluidine blue stain revealed a number of mast cells within the myxomatous stroma surrounding the tumor [Figure 2d]. We diagnosed it cellular neurothekeoma. Eighteen months after surgery, the patient was free from recurrence.

Figure 1

A reddish, solid nodule sized 3.5 × 3.5 mm on the left side of the upper lip

Figure 2

(a) Histopathological specimen showed lobular nodules on the shallow dermis, and the border of nodules was clear (hematoxylin–eosin stain). (b) The nodules were composed of cells which have a myxoid matrix and a spindle-shaped nucleus. (c) The tumor cells were positive for NGF. (d) There were a number of mast cells within the tumor nests and the myxomatous stroma surrounding the tumor (toluidine blue stain)

Although previous studies have suggested that neurothekeoma and nerve sheath myxoma are same diseases, Fetsch et al. argued that they were, in fact, different diseases.[1] WHO/IARC Classification of Tumours (Fourth Edition) classifies neurothekeoma as classic type (S-100 positive) or cellular type (S-100 negative). The head and neck are frequent sites of occurrence for neurothekeoma; however, the occurrence on the lip, as in the present case, is rare. To date, only five cases of neurothekeoma on the lip have been reported including our case.[2345] The age of patients ranged from 6 months to 35 years old, and female patients were observed in four cases including our case. The sizes of tumors ranged from 3.5 to 10 mm, and S-100 positive case was only one (one case was not tested for S-100). The triggering factor may be minor trauma, which however is not proven.

In the present case, toluidine blue stain revealed a number of mast cells within the tumor nests as well as in the myxomatous stroma surrounding the tumor; however, the number of mast cells was higher in the stroma than the tumor nests. NGF was detected on the tumor cells. NGF stimulates activation of mast cells and mediates increased accumulation of mast cells. Therefore, tumor-derived NGF may contribute to the increased number of mast cells in neurothekeoma in our case. Also, mucin was abundant in the tumor nests. Our case may suggest that tumor cells contribute to mast cell increase via NGF and mucin deposition. Alternatively, mast cells may stimulate tumor cells to produce mucin, but further studies are necessary.