Making The Case For Excising That ‘Ganglion Cyst’

How many times a week do we each see a patient presenting with a mass on the top of the foot? On exam, it is soft and movable along the course of the tibialis anterior or extensor tendon. Some of these patients have just noticed the mass and some say they have had it for years. Many have had previous treatment or aspiration, and others have been diagnosed confidently by another practitioner on sight alone. However, is anyone really able to say for certain that this is a correct identification of the mass without biopsy?  

In the past month alone, I have excised three of these assumed ganglion cysts, only to find that they were not ganglion cysts at all. All were on the dorsal aspect of the midfoot and seemed likely to be associated with a tendon sheath. All had been diagnosed by another physician as a ganglion cyst, years prior, with the recommendation to not do anything if it did not cause pain. Two of the three cysts had been aspirated with patients being told that the viscous or bloody fluid found was in line with the diagnosis of ganglion cyst. Yet, when I removed these masses surgically, the subsequent pathological examination revealed a schwannoma, an organized thrombus and a hidradenoma.

When the pathologist called me to talk about what was ultimately diagnosed as a hidradenoma, he shared that he could not be sure that he was not looking at an aggressive digital papillary adenocarcinoma or hidradenocarcinoma. For that reason, he was forwarding the specimen for a second opinion elsewhere. Luckily for my patient, the second pathologist ruled out hidradenocarcinoma and diagnosed the mass as nodular hidradenoma, which is also known as acrospiroma or clear cell hidradenoma.

Nodular hidradenoma (NH) is a relatively rare tumor of the sweat gland duct, which mainly occurs in female adults. Nodular hidradenoma most commonly occurs in the head and anterior surface of the trunk, but rarely in the extremities. The tumors are firm dermal nodules that may be attached to the overlying epidermis and range from 0.5 to three cm in size. These lesions may enlarge slowly and can show serous discharge. Surgical excision is curative and local recurrence is rare.¹

There have been multiple reports of malignant transformation in longstanding nodular hidradenoma, including one case of metastasis from a mass in the foot and cases occurring in the lower leg.^2,3 Unlike benign nodular hidraenoma, malignant nodular hidradenoma shows potential for recurrence and metastasis to bone, visceral organs and lymph nodes.³

My patient with nodular hidradenoma is a 28-year-old male who reported having aspiration of the mass 10 years earlier. It is likely that his previous podiatrist saw the serous drainage of nodular hidradenoma and mistook it for the viscous fluid of a ganglion cyst. Telling a patient that a mass is benign without biopsy is irresponsible and can be catastrophic. While each of the masses I excised this month are benign, each type (nerve, vascular and sweat gland respectfully) can be or may transform to malignancy and metastasis. All appeared in most ways to resemble a ganglion at skin surface but a closer look surgically revealed a much different story. 

Dr. Schwartz is the Scientific Conference Chair and a Past President of the American Association for Women Podiatrists. She is board-certified in foot surgery by the American Board of Foot and Ankle Surgery and practices with Foot and Ankle Specialists of the Mid-Atlantic in Washington, DC and Chevy Chase, MD. 

References

1. Shahmoradi Z, Mokhtari F. Clear cell hidradenoma. Adv Biomed Res. 2013;2:40.

2. Kiran Kailas C, Nanjappa N, Srikantaiah HC. Hidradenoma: a skin adnexal tumour, case report and literature review. J Pat Care. 2015;1:1.

3. Ngo N, Susa M, Nakagawa T, et al. Malignant transformation of nodular hidradenoma in the lower leg. Case Rep Oncol. 2018;11(2):298-304.