Ultrasound for HS: Tunnels, Disease Extent & Surgery Planning

Canonical URL: https://www.acneinversa.life/en/blog/hs-ultrasound/
Markdown URL: https://www.acneinversa.life/en/blog/hs-ultrasound.md
Plain text URL: https://www.acneinversa.life/en/blog/hs-ultrasound.txt
Language: en
Category: Diagnosis
Published: 2026-09-11
Last updated: 2026-09-11
Last editorially reviewed: 2026-09-11
Next scheduled review: 2027-09-11
Evidence strength: Moderate evidence — Backed by consistent observational studies or smaller trials.
Author: Dr. rer. nat. Dennis Alexander Kwiatkowski (Biochemist, Scientific Writer and Pharma Expert)
Scientific editor: Dr. rer. nat. Dennis Alexander Kwiatkowski
Reviewer qualifications: Biochemist, Scientific Writer and Pharma Expert
Review scope: Scientific literature, clinical guidelines, sources, and editorial clarity
Clinical reviewer: No independent clinical review
Tags: Acne Inversa, Hidradenitis Suppurativa, HS, Diagnosis, ultrasound, sonography, high-frequency ultrasound, tunnels, doppler, surgery planning, diagnosis
High-frequency skin ultrasound can sometimes reveal HS tunnels and deeper disease that aren't obvious on examination. What ultrasound can and can't show, when it may help, and how it relates to diagnosis, monitoring and surgery planning.

Medical disclaimer: This website is for general educational information only and does not replace medical advice, diagnosis, or treatment. Please speak with qualified medical professionals about symptoms or treatment decisions.

60-second summary

- HS remains primarily a clinical diagnosis, based on history and examination, not a single imaging test.
- High-frequency skin ultrasound can sometimes show tunnels, fluid collections and deeper changes not obvious on examination.
- In one multicentre study, ultrasound reclassified 44.7% of clinically mild (Hurley I) patients to a more severe stage.
- A 2026 international consensus supports ultrasound for staging, monitoring, image-guided procedures and surgery planning in HS.
- Not everyone with HS needs ultrasound, and not having access to it does not mean your care is inadequate.

What this means: Ultrasound is an additional tool, not a replacement for a skilled clinical exam. It tends to matter most when one specific question — how far a tunnel extends, whether a collection is hidden, whether it would change a procedure — can't be answered by looking and feeling alone.

What we are less certain about: How much ultrasound-guided care improves long-term outcomes, beyond changing staging on paper, isn't fully settled. Access to clinicians trained in dermatologic ultrasound also varies a great deal between countries and even between clinics in the same city.

What you can do next: Before asking about imaging, get clear on the specific question you'd want it to answer — for example, how far a suspected tunnel extends, or whether it could change a surgical plan.

Article

Most hidradenitis suppurativa diagnoses do not begin with a scan. HS is diagnosed clinically — from what kind of lesions occur, where they occur, and whether they recur — not from a blood test or an imaging result. That hasn't changed, and this article doesn't argue that it should.

But HS doesn't exist only on the skin surface. Tunnels, fluid collections and inflammatory change can extend well beyond what's visible or palpable at the surface. That's where high-frequency skin ultrasound can sometimes add information a clinical exam alone can't reach.
Educational content only. This article explains what high-frequency skin ultrasound can and can't show in HS, and when clinicians may use it. It doesn't tell you whether you personally need it, and it's not a substitute for individualized medical advice.

Key takeaways

- HS remains primarily a clinical diagnosis. Ultrasound is not a test that independently proves or rules out HS.
- High-frequency skin ultrasound can sometimes show tunnels, fluid collections, and deeper structural or vascular changes that aren't obvious from the surface.
- In the largest published comparison, ultrasound reclassified a substantial share of clinically mild (Hurley I) patients to a more severe stage, and changed the proposed treatment approach more often than clinical exam alone.
- A 2026 international expert consensus supports ultrasound's use for diagnosis and staging, monitoring, image-guided procedures, and surgery planning — while acknowledging that access and training remain real obstacles.
- Not needing, or not having access to, ultrasound doesn't mean your HS care is substandard. A skilled clinical exam remains the foundation.

What kind of ultrasound are we talking about?

This is high-frequency dermatologic ultrasound — a small probe placed on the skin with gel, sending sound waves into the tissue and reconstructing an image from the returning echoes. It's the same underlying physics as any other ultrasound, but the equipment and frequencies used for skin are different from what's used to scan, say, an abdomen: higher-frequency probes trade a shorter depth of view for much finer detail in superficial tissue, which is exactly what HS assessment needs.

Dermatologic ultrasound is used for a range of inflammatory skin conditions, skin lesions, lymph nodes and preoperative planning. The University Medical Center Hamburg-Eppendorf (UKE), for instance, lists Acne inversa specifically among the inflammatory conditions it uses skin sonography to monitor and assess before procedures.

Does ultrasound diagnose HS?

Not by itself. HS remains primarily a clinical diagnosis, built from the combination of typical inflammatory lesions, typical body locations, recurrence over time, and ruling out other explanations. There's no single ultrasound finding that substitutes for that clinical picture. Ultrasound is better understood as additional anatomical information — sometimes useful, never sufficient on its own.

What can ultrasound actually show in HS?

Depending on the equipment and the examiner's experience, ultrasound can visualize several things beneath the surface.

Tunnels. HS tunnels can travel further, and connect more areas, than a surface opening suggests. Ultrasound can help characterize a tunnel's course, depth and morphology — the 2026 international consensus specifically lists diagnostic criteria and staging built around these features as areas of expert agreement.

Fluid collections. Ultrasound can identify pockets of fluid beneath the skin, which can help distinguish structures that might feel similar on palpation. A detected collection doesn't automatically mean a procedure is needed; the finding still has to be interpreted alongside the clinical picture.

Pseudocysts and follicular changes. Research using high-frequency and ultra-high-frequency probes has described distorted or enlarged hair follicles and small cyst-like structures associated with HS. These are mainly relevant to specialists and researchers rather than something a patient needs to interpret.

Vascular activity around deeper structures. Colour Doppler ultrasound can detect increased blood flow consistent with inflammation. A 2026 study evaluated 312 tunnels across 84 patients at three centres and found Doppler activity in 91% (284/312) of them; purulent drainage correlated with Doppler positivity in every case, and dermal (type A) tunnels — which were universally non-draining in this study — still showed Doppler positivity in the majority of cases, with 88% showing a pain-plus-erythema combination. The authors proposed that an "active" tunnel might be better defined as one with purulent drainage, or pain combined with erythema or induration, rather than by drainage alone.

Why can ultrasound find more than a physical exam?

A skilled clinician learns a great deal from looking, palpating, and asking about drainage, pain and recurrence — but hands and eyes mainly assess what can be felt or seen from the outside. HS can extend through the dermis and into deeper tissue in ways that aren't always palpable. A 2026 commentary in the Journal of the European Academy of Dermatology and Venereology described this directly: high- and ultra-high-frequency ultrasound has progressively revealed what it called "hidden HS" — tunnels, fluid collections, pseudocysts and follicular alterations frequently missed on physical examination alone.

How often does ultrasound actually change the clinical picture?

The most concrete evidence here is a 2019 multicentre study of 143 HS patients that directly compared clinical staging with ultrasound staging. On clinical examination, 38 patients were staged Hurley I, 70 as Hurley II, and 35 as Hurley III. On ultrasound, the same patients were staged 21, 80 and 42 respectively — a statistically significant shift toward more severe disease (P < 0.01). Among patients staged Hurley I clinically, 44.7% moved to a more severe stage once ultrasound was factored in.

The study also looked at what clinicians would have done differently. Based on clinical exam alone, they would have maintained, increased or decreased treatment in 44.1%, 54.5% and 1.4% of cases respectively; incorporating ultrasound shifted those figures to 31.5%, 67.1% and 1.4% — meaningfully more patients where treatment escalation was proposed.

This is one study, from 2019, and it shouldn't be read as "nearly half of mild HS is secretly severe." Its narrower and better-supported lesson is that clinical examination can underestimate structural disease extent in a meaningful minority of patients — which is a different claim, and a more defensible one.

When might ultrasound be worth discussing?

There's no checklist that determines who "needs" ultrasound, and this article isn't going to invent one. Situations where it may be worth raising with a clinician include:

- A suspected tunnel whose extent is unclear — for example, an area that keeps draining but you and your clinician aren't sure how far it runs.
- Symptoms that feel more extensive than what's visible — a painful area under the skin that seems considerably wider than any surface opening.
- Recurrent disease at one site, where understanding the underlying anatomy could change the management conversation.
- Before a procedure or surgery, particularly when the surgical team wants a clearer picture of tunnels or collections before deciding how much tissue the procedure should address.
- Selected treatment monitoring, where a clinician wants to assess change beneath the surface rather than relying only on what's visibly countable.

The 2026 international consensus covers all five of these broad domains — diagnosis and staging, monitoring, image-guided procedures, and surgery planning — as areas where the expert panel found strong agreement.

Why might ultrasound matter before HS surgery?

A visible tunnel opening a centimetre wide doesn't guarantee the structure underneath has the same shape or boundary. That gap between what's visible and what's actually there is exactly what matters when a surgical team is deciding how much tissue a procedure needs to address.

Ultrasound isn't there to dictate the procedure. It can add information about a tunnel's depth, direction, nearby collections and connections to other areas — the kind of anatomical detail that's genuinely hard to establish by inspection and palpation alone. Surgery planning is one of the domains the 2026 consensus specifically supports, and it lines up with earlier clinical literature on ultra-high-frequency mapping ahead of HS procedures. See our Surgery Planner (/en/hs-surgery-planner/) for the broader set of questions worth preparing before a procedure.

Can ultrasound tell whether a tunnel is active?

Sometimes, and with real nuance. Colour Doppler can detect blood flow consistent with inflammation, and the 2026 tunnel study described above found that signal in the large majority of tunnels evaluated — including some that weren't externally draining. That's a genuinely useful concept: a tunnel doesn't have to be visibly draining to show signs of ongoing inflammatory activity.

What it isn't is a simple pass/fail test you could apply yourself. A single scan showing no detectable Doppler flow doesn't prove a tunnel is inactive — blood flow can be intermittent, technique-dependent, and hard to standardize between machines and operators. This is squarely a clinical interpretation, not a number to self-diagnose from.

Can ultrasound show whether my treatment is working?

Potentially, in selected specialist settings. Researchers use ultrasound to track features like lesion and tunnel dimensions, fluid collections and vascularity over the course of treatment, and monitoring is one of the domains explicitly addressed by the 2026 consensus. That said, routine assessment of how HS treatment is going still relies mainly on clinical examination, symptoms, lesion counts and your own account of what's changed — sometimes supplemented by photographs. Don't assume ultrasound needs to bracket every treatment you try; most treatment monitoring in HS still happens without it.

Does an ultrasound hurt, and how should I prepare?

The scan itself — probe and gel on the skin — involves no incision. But HS lesions can be extremely tender, and probe pressure over an inflamed nodule, an abscess, or a recently operated area can genuinely hurt. Say so if a region is particularly painful; there's no reason to tolerate unnecessary pressure to "prove" how bad it is.

Preparation is usually minimal. It can help to know which area has been repeatedly symptomatic, be ready to describe where drainage openings have appeared, and mention any prior procedures in that region. Don't squeeze, drain, or otherwise manipulate a lesion beforehand to try to make it "easier to see" — that doesn't help the assessment and can hurt unnecessarily.

Not all ultrasound is equally useful for HS

HS-specific ultrasound assessment ideally needs suitable high-frequency equipment, familiarity with dermatologic structures, and specific knowledge of HS tunnel and lesion patterns — which is exactly why the 2026 consensus devotes explicit attention to operator training and technical standards, not just clinical indications. A general radiology department may be excellent at what it does without routinely performing this specific kind of assessment. The more useful question to ask is "Does anyone here use high-frequency skin ultrasound specifically for HS, and would it change how we understand this area?" — not simply "Can I get an ultrasound?"

Is ultrasound standard everywhere? Does not having it mean my care is inadequate?

No, on both counts. Availability varies enormously between countries, hospitals and individual dermatology practices, and a strong international consensus doesn't mean every clinic already has the equipment or training in place — the consensus itself is explicit that implementation remains a real challenge. A skilled clinical exam is still the foundation of HS care, and plenty of sound treatment decisions get made without imaging. The relevant question isn't "should everyone with HS get ultrasound," it's "would seeing what's under the skin answer something examination and history haven't."

Ultrasound versus MRI

Both can show structures beneath the skin, but they aren't interchangeable. Ultrasound offers real-time imaging, high resolution for superficial tissue, the ability to examine one specific area dynamically, and Doppler assessment of vascularity — useful during some guided procedures too. MRI covers a much wider field and can be more valuable for selected deeper or anatomically complex disease, such as some perianal presentations where deeper pelvic anatomy needs consideration. Your clinician chooses based on the clinical question at hand, not on which technology sounds more advanced.

Ultrasound versus photographs and the Symptom Tracker

These tools answer different questions, and none of them replaces the others. Photographs document what's visible — distribution, redness, swelling, drainage, scarring — over time; see our Photo Guide (/en/hs-photo-guide/) for how to do that usefully before an appointment. The Symptom Tracker (/en/symptom-tracker/) can show pain, drainage, flares and functional impact over time. Ultrasound can show anatomy beneath the surface that neither a photograph nor a symptom log can ever reach. A photograph can't see through skin, and ultrasound can't tell you how the disease has behaved between visits — they're complementary, not competing.

Five questions worth asking your dermatologist

1. Do you think there's a tunnel or collection beneath this area that we can't fully assess by exam?
2. Would ultrasound tell us something examination alone can't answer clearly?
3. Would the result actually change treatment or procedure planning?
4. If surgery is being considered, would mapping the tunnel first change how it's approached?
5. Is high-frequency dermatologic ultrasound available here, or through a specialist HS centre?

That's a more useful conversation than asking for "an ultrasound" in the abstract.

When ultrasound probably isn't the first problem to solve

If the open question is still "are these recurring lesions HS at all," the priority is a proper clinical assessment and a clear history — not imaging. And urgent symptoms — fever, rapidly spreading redness, severe systemic illness, or pain that's rapidly worsening — shouldn't wait on specialist imaging. See when to contact your healthcare team (/en/when-to-get-medical-help-hs/) for that distinction.

The bottom line

HS can extend beneath what's visible on the skin, and high-frequency ultrasound can sometimes reveal tunnels, deeper collections, structural change and inflammatory activity that are genuinely hard to assess from the surface alone. That's why a 2026 international expert consensus now supports its use for staging, monitoring, image-guided procedures and surgery planning in HS.

It's not a replacement for your history, a skilled physical exam, or clinical judgment, and it's not something every person with HS needs. The more useful question isn't "should everyone with HS get ultrasound" — it's "would seeing what's happening under the skin change what we do next."

Choose the next step:

- Understand how HS is diagnosed → Diagnosis Guide (/en/blog/hidradenitis-suppurativa-diagnosis-what-to-expect/)
- Preparing for a procedure → HS Surgery Planner (/en/hs-surgery-planner/)
- Document what your skin looks like between visits → HS Photo Guide (/en/hs-photo-guide/)
- See the full range of HS treatments → Treatment Options (/en/hub/treatment-options/)

FAQ

Can ultrasound detect HS tunnels?

Yes. High-frequency dermatologic ultrasound can identify tunnels beneath the skin and help characterize their depth, course and morphology — sometimes more extensively than what's visible or palpable at the surface. It's an additional clinical tool, not a test that independently confirms HS.

Do I need ultrasound to be diagnosed with HS?

No. HS is primarily a clinical diagnosis, based on the pattern of typical lesions, typical body locations and recurrence over time. Ultrasound is not required to reach a diagnosis and doesn't replace that clinical assessment — it can add information in selected situations.

Can ultrasound show HS that can't be seen on the surface?

It can detect subclinical or deeper structural changes that aren't obvious on examination. In one multicentre study of 143 patients, ultrasound reclassified 44.7% of patients initially staged as Hurley I (the mildest category) on clinical exam to a more severe stage.

Can ultrasound tell whether a tunnel is inflamed or active?

Colour Doppler ultrasound can detect blood flow associated with inflammation, and a 2026 study found Doppler activity in the majority of evaluated tunnels, including some that weren't visibly draining. That doesn't make Doppler a simple at-home "active or not" test — interpretation takes clinical expertise, and a tunnel without detectable Doppler activity on one scan isn't automatically "inactive."

Is ultrasound useful before deroofing or HS surgery?

It can be. Mapping tunnels and planning the extent of a procedure are among the uses supported by the 2026 international HS-ultrasound consensus, and by earlier work on preoperative ultra-high-frequency mapping.

Is skin ultrasound the same as a routine abdominal or obstetric ultrasound?

The underlying physics are the same, but HS assessment typically uses much higher-frequency probes suited to superficial skin and soft tissue, and it requires familiarity with dermatologic and HS-specific anatomy that a general radiology scan doesn't assume.

Does every HS specialist offer ultrasound?

No. Equipment, training and access vary substantially between countries, hospitals and individual dermatology practices. The field is actively being built out, not something every clinic already has in place.

Is MRI better than ultrasound for HS?

Not universally — they answer different questions. Ultrasound offers real-time, high-resolution imaging of superficial tissue and Doppler assessment of vascularity; MRI covers a wider field and can be more useful for selected deeper or anatomically complex disease, such as some perianal presentations. The right test depends on the clinical question, not which technology sounds more advanced.

References

1. Wortsman X, Alfageme F, Dini V, et al. International consensus statement on the use of ultrasound in hidradenitis suppurativa. - Journal of the European Academy of Dermatology and Venereology, 2026 - https://doi.org/10.1111/jdv.20600
2. Vilarrasa E. From 'nice to have' to 'must have': Integrating ultrasound into routine care of hidradenitis suppurativa. - Journal of the European Academy of Dermatology and Venereology, 2026 - https://doi.org/10.1111/jdv.70312
3. Martorell A, Alfageme Roldán F, Vilarrasa Rull E, et al. Ultrasound as a diagnostic and management tool in hidradenitis suppurativa patients: a multicentre study. - Journal of the European Academy of Dermatology and Venereology, 2019 - https://doi.org/10.1111/jdv.15710
4. Martorell A, Melgosa Ramos FJ, Navarro Guillamón P. Beyond Drainage: Clinical-Ultrasound Correlation Supports a Broader Definition of the Active Tunnel in Hidradenitis Suppurativa. - Dermatology and Therapy, 2026 - https://doi.org/10.1007/s13555-026-01828-5
5. Mendes-Bastos P, Martorell A, Bettoli V, Matos AP, Muscianisi E, Wortsman X. The use of ultrasound and magnetic resonance imaging in the management of hidradenitis suppurativa: a narrative review. - British Journal of Dermatology, 2023 - https://doi.org/10.1093/bjd/ljad028
6. Zouboulis CC, Bechara FG, Benhadou F, et al. European S2k guidelines for hidradenitis suppurativa/acne inversa part 2: Treatment. - Journal of the European Academy of Dermatology and Venereology, 2025 - https://doi.org/10.1111/jdv.20472
7. Medizinische Sonografie — Institut für Versorgungsforschung in der Dermatologie und bei Pflegeberufen (IVDP). - University Medical Center Hamburg-Eppendorf (UKE) - https://www.uke.de/kliniken-institute/institute/versorgungsforschung-in-der-dermatologie-und-bei-pflegeberufen/sprechstunden/medizinische-sonografie.html