Why use ultrasound in hidradenitis suppurativa?

Ultrasound is an important tool for the early and accurate diagnosis of skin lesions, especially when they are small or not palpable.10 It also helps identify subclinical fistulas,16 which can affect disease staging.8,10,13,17,18 Clinical scores alone may underestimate the degree of disease involvement. Additionally, Doppler ultrasound allows mapping of the extent and activity of skin lesions, facilitating the assessment of treatment effectiveness.10,13,15 Corticosteroid infiltration can be guided by ultrasound to improve precision, with better results.19,20 In the case of fistulas, ultrasound helps to determine the depth, which influences the appropriate treatment, whether with immunobiologicals or surgical. The combined use of immunobiologicals and ultrasound before surgery is effective in preventing recurrence and accurately determining surgical margins. Additionally, ultrasound can be used to evaluate possible recurrences after surgery.10,21

The patient should be examined and the scores used to classify severity before performing the ultrasound. Then ultrasound severity scores should be applied. The easiest ultrasound score is the SOS HS (Table 1),15,18,23 which uses the number of ultrasonographic detected lesions (in a similar way to Hurley) to define stages I, II or III, with the latter being the most severe.

Ultrasound can be used to monitor response to treatment. It should be performed at the first consultation,15,18 after eight weeks of antibiotic use,15 in weeks four, 12 and 24 when using immunobiologicals,24 12 weeks after infiltration19,20 and six months after surgery to evaluate postsurgical recurrence.21

Ultrasound must be configured with the focal point in the first 3 cm from the top of the screen and must be adjusted for dermatological ultrasound.17 The frequency, gain and image volume must be kept constant to prevent problems with reproducibility.15,23

Dermatological ultrasound can use a frequency between 13.5 and 100 MHz, with 20-25 MHz examining the epidermis and dermis and 50-100 MHz restricted to the epidermis.25 The recommendation is to use several probes between 5‒22 MHz.8,10,13–15,22–24,26 It is always recommended to use a linear probe.8,14,22,23,27

The examination should preferably be performed by the same investigator,14,15,22,23 who should be trained in the ultrasound technique and in dermatology13,17,21,26 or by dermatologists with at least 10 years experience in HS and two ultrasound operators who have completed training courses.18

When performing Doppler ultrasound examinations in patients with HS, it is important to follow a sequence of steps to ensure the effectiveness of the procedure. First, it is necessary to perform the examination after the clinical assessment of the patient, taking into account the established criteria.8,18 Additionally, it is essential to to explain the procedure to the patient and obtain information about lesion evolution.

Before starting the examination, it is recommended to apply an adequate amount of gel to the area to be examined or directly to the ultrasound probe.14,17 Subsequently, visual inspection and palpation of the lesional and perilesional area are performed in a well-illuminated place. For a better observation, it is important to reduce the light in the room and position the lesion close to the operator and the probe.17

During the examination, the probe should be gently positioned perpendicular to the lesion, as shown in Fig. 1.27 It is important to apply little pressure and stabilize the hand with the help of the fifth finger. Image capture must be done in two perpendicular axes, covering both the lesional and perilesional areas.8,10,14,17,22 If necessary, one can compare the images with others obtained from the contralateral area.

Figure 1.

Amount of gel to be used and perpendicular positioning of the probe.

(0.23MB).

Moreover, Color Doppler analysis is recommended to evaluate the vasculature pattern of the lesional and perilesional area, as well as evaluate vessel caliber. If necessary, the spectral curve can be used to differentiate between veins and arteries and detect flow velocity.17

During the evaluation of patients with HS, it is necessary to follow a sequence of steps for a complete and systematic analysis. First, it is important to evaluate all existing lesions,8,27 in at least two different regions.10 Additionally, it is essential to always examine the axillary and inguinal regions, as well as the perineal and perianal areas.8,10,18 If it is impossible to do it that way, evaluate at least all symptomatic areas.15

For a standardized approach, it is recommended to use a specific sequence, starting from top to bottom and medial to lateral regions. During the examination, it is necessary to identify the type of lesion according to its characteristics and describe the dermal changes.10 It is also important to measure the size of the lesions and the maximum diameter of nodules, abscesses and fistulas. The precise location of the lesions must be described.10,15,23,24,27

Numbers can be used to facilitate the identification and recording of lesions, for example, C1, C2 for collections, and F1, F2 for fistulas. If the patient has multiple fistulas, it is recommended to select the largest one for a more accurate evaluation.21,28

Moreover, describing the exact location of each lesion can be challenging due to the number of lesions. Therefore, the authors suggest the use of the quadrant classification of the UQHS anatomical areas – Ultrasound Quadrants in Hidradenitis Suppurativa (Figs. 2–4) to assist in the description of the report. This classification was designed using anatomical references such as the anterior, middle and posterior axillary lines, to form the quadrants. It is also possible to incorporate the description of lesions in “hours” and outer, middle and inner sections (for each quadrant). For example, in Fig. 2, there is a lesion in the superior medial quadrant of the left axilla, at 12 o'clock, in the inner section. Thus, it is possible to locate the lesions more precisely.

Figure 2.

Axillary and intermammary region.

(0.39MB).

Figure 3.

Intermammary region.

(0.25MB).

Figure 4.

Inguinal region.

(0.32MB).

Figures 2–4.

The ultrasound findings already described in the literature are:11,13,16

• 1.

  Dilatation of hair follicles.

• 2.

  Changes in dermal thickness and echogenicity (Fig. 5).

  
  

  Figure 5.

  Changes in the thickness and echogenicity of the dermis.

  (0.19MB).
• 3.

  Anechoic or hypoechoic dermal pseudocysts – round or oval hypoechoic and anechoic structures in the dermis and/or hypodermis measuring <1 cm, which may clinically correspond to nodules or abscesses (Fig. 6).

  
  

  Figure 6.

  Pseudocyst.

  (0.15MB).
• 4.

  Anechoic fluid collections with echoes (debris) – hypoechoic or anechoic dermal fluid and/or hypodermic sac-like structure connected to the base of the enlarged hair follicle, clinically corresponding to an abscess or fistula (Fig. 7).

  
  

  Figure 7.

  Fluid collections.

  (0.11MB).
• 5.

  Hypoechoic fistula/fistulous tracts in the dermis and subcutaneous tissue – dermal or hypodermal hypoechoic or anechoic band-like structure connected to the base of an enlarged hair follicle (Fig. 8).

  
  

  Figure 8.

  Fistulae.

  (0.16MB).

More recently, an international consensus of experts validated, in addition to the abovementioned lesions, “hair tracts”, or fragments of hair, with a trilamellar, bilaminar or monolaminar appearance and an hyperechoic linear pattern (Fig. 9).9,13

Figure 9.

“Hair tracts”.

(0.11MB).

Vascularization evaluation with Doppler provides an objective assessment of the degree of inflammation and disease activity. It can be classified as absent, peripheral, internal or mixed (Fig. 10).15,22–24

Figure 10.

Type of vascularization on Doppler.

(0.42MB).

It is also possible to grade the amount of vascularization23 as high, if there are multiple signs, moderate if there are some signs of flow, minimal if there are a few points and absent. Nodules and abscesses have a peripheral vascularization pattern, simple fistulas, peripheral and mixed, and complex fistulas show a mixed pattern. Nodules show moderate to low amount of vascularization20 and abscesses and fistulas show a high to moderate degree of vascularization.13,23 As the disease becomes chronic, the vascularization changes from peripheral to mixed.23

Another important complementary assessment is the grading of fibrosis (Fig. 11),16 which may appear as absent (grade 0), as a thin peripheral hypoechoic band with a fibrillar pattern (grade 1) or as a thick, peripheral hypoechoic band with a fibrillar pattern that invades the fistula lumen and produces a hypoechoic halo that is transversely visible (grade 2).

Figure 11.

Grading of fibrosis.

(0.29MB).

A fistula with a high degree of fibrosis is chronic and requires surgical treatment.

Finally, it is also possible to observe and grade perilesional edema, which directly correlates with inflammation and associated symptoms such as pain (Fig. 12).22,24 It may be absent (grade 0), show hypodermic hyperechogenicity (grade 1) or hypodermic hyperechogenicity and anechoic fluid among the hypodermal adipose lobes (grade 2).

Figure 12.

Grading of perilesional edema.

(0.33MB).

Another possible finding are reactive lymph nodes that have an elliptical well defined shape, with hypoechoic cortical thickening, and an hyperechoic medulla in the central area (Fig. 13).17,23,28 Normally they are 1 cm in diameter and the Doppler assessment shows hilar vessels in the central area or at one of the borders.10,17,25

Figure 13.

Reactive lymph node, without important changes.

(0.29MB).

Determination of surgical margins intraoperatively through ultrasound examination can prevent recurrence. The technique used to determine ultrasound surgical margins involves first determining a 0.5 cm width clinical margin and then explore the area identified with ultrasound, transversely. Then, increase the area to be excised if subclinical lesions are present, repeating the process until there are no more lesions.22

The medical record should contain the type of lesion, anatomical location (Figs. 2‒4), diameter, vascularization status, description of relevant surrounding structures and inflammatory activity and degree of edema using Doppler.

As HS lesions may be draining fluids, it is recommended to use plastic covers for the probe, without significantly compromising the images obtained. After each patient examination, the probe should be cleaned with an alcohol solution.

Despite the various advantages, available ultrasound devices do not allow the identification of lesions smaller than 0.1 mm, and do not show pigment or lesions exclusively intraepidermal,8,17 with no real impact in the assessment of HS.