Pre-Operative Ultrasonography Guide for Hidradenitis Suppurativa

Hidradenitis suppurativa (HS) is a chronic inflammatory skin condition characterised by abscesses, nodules, and sinus tracts [1]. Although diagnostic and staging criteria for HS are based on clinical findings, this may underestimate the severity and extent of disease [1]. High frequency ultrasound (HFU) has been shown to be highly sensitive when combined with clinical examination in delineating the extent of HS lesions [1]. It provides important details on lesion morphology and severity, aiding in tracking disease progression and guiding treatment options. Thus, it has received a high-grade rating as a valid biomarker for HS [2]. As such, pre-surgical margin mapping with HFU, before carbon dioxide (CO₂) laser surgery—an effective treatment for HS, may reduce recurrence rates. However, there is minimal existing literature regarding the margin mapping methodology. This letter provides a practical framework for ultrasound mapping of HS lesions before CO₂ laser excision.

It is important to become familiar with ultrasound features of skin layers to delineate HS lesions from healthy tissue. In healthy skin, the epidermis is the outermost layer, appearing as a hyperechoic line [3]. Beneath, lies the dermis, a thick and heterogeneous layer with hyperechoic reflections of collagen fibres [3]. Lastly, the hypodermis sits below the dermis, appearing as a hypoechoic fat interdispersed with linear hyperechoic reflections representing connective tissue [3]. Features of HS on ultrasound include increased dermal thickening, lower echogenicity of the dermis suggesting edema, anechoic or hypoechoic fluid deposits, and widening of hair follicles [3, 4]. Additionally, fistulous tracts appear as anechoic or hypoechoic band-like structures in the dermis or hypodermis, while pseudocysts appear as oval-shaped hypoechoic or anechoic nodular structures [4].

Regarding HFU imaging specific to margin mapping before CO₂ laser excision, the following methodology is recommended. After palpating the specific lesions to estimate extent, the US probe should be positioned perpendicular to the lesion. This should be done while applying minimal pressure and using the little finger to keep the hand steady and elevated, while in contact with the skin through a gel bed (Figure 1). A 1−2 cm gel bed is recommended for better visualisation of changes in superficial features [5]. A lower frequency probe, such as 12 MHz, may be used initially to find deeper lesions, as these probes provide greater depth of imaging, although at a relatively lower resolution [5, 6]. A higher frequency probe, with range from 15 to 22 MHz, may be utilised next to visualise areas of interest in greater detail [5, 6]. Among the characteristic HFU features of HS, change in dermal thickening was identified as the most pertinent feature when performing preoperative margin mapping (Figure 1). As such, specific to margin mapping, once a sinus tract or fluid deposit has been located, the operator must follow it to where it ends, which corresponds to the transition point between normal and thickened dermis. This should be marked with a skin marker and performed every 1−2 cm around the lesion to demarcate the area of excision (Figure 2). Isolated lesions within 2−3 cm on the surrounding skin should be evaluated for the presence of any sinus tracts connecting them to the main lesion, as that would impact the area to be excised. Furthermore, the Doppler feature may be utilised to avoid areas with high blood flow.

It is highly important to excise all diseased tissue to achieve cure and reduce recurrence. HFU imaging, employing the methodology described above, can help achieve this by eliminating inter-operator variability in clinical examinations [2]. We analysed data from three patients who underwent HFU imaging before the CO2 surgery and had no recurrence demonstrating the effectiveness of HFU and our technique for pre-surgical mapping before CO₂ laser surgery. The demographic details, lesion site and size and days post-surgery when no recurrence was observed are as follow: The first patient was a 46-year-old male who had surgery on the left axilla (96 cm²), with wound closure at 154 days and no recurrence. The second patient was a 46-year-old female who underwent surgery on the right axilla (130 cm²), achieving closure at 147 days with no recurrence. The third patient, a 24-year-old female, had surgery on the right axilla (63 cm²), with closure at 112 days and no recurrence. Considering these promising preliminary findings, future large-scale studies are warranted to evaluate the correlation between HFU mapping of HS lesions before CO₂ laser excision and recurrence rates.

Dr. Indermeet Kohli and Dr. Iltefat Hamzavi created the methodology and edited the manuscript, Dr. Redina Bardhi, Mohsen Mokhtari, and Dr. Mavra Masood performed the experiments and drafted the manuscript, and Dr. Ziglar and Sydney Colbert collected data.

All patients in this manuscript have given written informed consent for participation in the study and the use of their de-identified data and their case details (including photographs) for publication. Institutional Review Board: 7851-18.

Iltefat Hamzavi: Bayer, UCB, HS Foundation, Boerhinger Ingelhei, Sonoma, Union therapeutics, Novartis, Jansen, Almirall, Merck, Clinuvel, Abbvie, Pfizer, Incyte, Jansen, Avita, Merck, Vimela, ITN, Galderma, Sonoma, Union therapeutics, MyDermPortal, Chemocentyx, Global Vitiligo Foundation, Arcutis, Unigen, Loreal/Laroche Posay, Ferndale Laboratories, Estee Lauder. The other authors declare no conflicts of interest.