The missing link: Cadaveric study highlights connection between solar elastosis, adenoid (reticulated) seborrheic keratosis

Key Points

Rochester, Minn. - Adenoid seborrheic keratosis (SK) occurs more commonly than medical literature to date has acknowledged, according to a recent postmortem study.

Because these lesions frequently occur in the context of pigmented actinic keratoses (AKs) or solar lentigines, a study co-author says, minute superficial shave biopsies of adenoid SKs could miss the peripheral AKs and solar lentigines.

Adenoid SKs

However, he says adenoid SKs possess flat surfaces.

In conducting the study, Dr. Shon tells Dermatology Times, "I wanted to emphasize that adenoid SKs are clinically, biologically and histologically different from the other types of SK."

Cadaver study

To help clarify such matters, Dr. Shon and colleagues obtained 55 cadavers, on which they identified and fully excised (with wide margins) 68 suspicious pigmented facial lesions. To Dr. Shon's knowledge, he says, the study provides the first postmortem analysis of adenoid SK.

Investigators fixed tissue samples in 10 percent buffered formalin and stained and processed samples through routine histological techniques; then a pathologist and two pre-doctoral pathology fellows evaluated the samples.

Of the 68 original lesions, Dr. Shon says he and his colleagues diagnosed five as pure solar lentigines and one as postinflammatory hyperpigmentation. They also diagnosed 60 SKs, of which 37 were adenoid type.

"In 11 of the 37 adenoid SKs," Dr. Shon says, "we also saw pigmented actinic keratosis (AK) with varying degrees of keratinocytes atypia. So, in approximately 30 percent of the adenoid SKs, we saw an association with pigmented AKs."

Furthermore, he says, virtually all of the adenoid SKs arose from solar lentigines.

'Continuous spectrum'

"Since adenoid SK almost always arises from solar lentigoes," Dr. Shon says, "we believe that solar lentigoes, adenoid SKs and pigmented AKs are all part of a continuous spectrum of lesions caused by chronic sun exposure.

"Microscopically," he says, "adenoid SK is unique compared to other types of SK."

Along with having a flat, smooth surface, adenoid (reticulated) SKs possess a proliferation of narrow, pigmented, lacelike strands of epithelium surrounded by a homogeneous fibroplasia, Dr. Shon says.

"We are the first researchers to describe this dermal fibroplasia surrounding the epidermis. That's the unique microscopic characteristic of the lesion," he says.

In a previous analysis of 108 SK lesions, researchers identified only 10 adenoid SKs, along with 71 acanthotic and 27 hyperkeratotic SKs. This sample also contained five invasive squamous cell carcinomas (SCCs), of which three were associated with adenoid SK (Maize JC, Snider RL. Dermatol Surg. 1995 Nov;21(11):960-962).

"These researchers believe that adenoid type SK is associated with invasive carcinoma," Dr. Shon says.

Linking SK and SCC

"Pigmented AK is a premalignant SCC lesion. And some authors believe that all AKs represent superficial SCC," Dr. Shon says.

From a clinical perspective, Dr. Shon says that because his study found that adenoid SKs frequently were surrounded by pigmented AKs or solar lentigines, minute superficial shave biopsies could miss these lesions.

"Microscopically," he says, "we saw a homogeneous fibroplasia in superficial papillary dermis. This fibroplasia actually pushes down solar elastosis. So, a very superficial shave biopsy will not catch the solar elastosis, which is microscopic evidence of sun-damaged skin."

If patients diagnosed with adenoid SK return a few months or years later with persistent lesions that have developed unusual characteristics, Dr. Shon says, "Then we should consider doing an additional biopsy, and regard the lesion with caution. That's the key message from this study."

Study limitations

Dr. Shon says that because all 55 cadavers used were Caucasian and originated in the New York area, this sample doesn't accurately reflect the diversity of the U.S. population.

Disclosure: Dr. Shon reports no relevant financial interests.