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. 2024 Nov 4;28(1):137–150. doi: 10.1007/s40477-024-00966-w

Trichosonography: ultrasound of alopecias and hair disorders

F J Rodríguez-Cuadrado 1,✉, C Martínez-Mera 1, G Roustan-Gullón 1, F Alfageme-Roldán 1
PMCID: PMC11947382  PMID: 39495405

Abstract

Trichology is the area of dermatology that focuses on the study, diagnosis and management of the different types of alopecia and hair and scalp disorders. In recent years, there have been great advances in the non-invasive diagnosis of these conditions, especially with trichoscopy and more recently with sonography. High frequency ultrasound study of the scalp, for which we propose the name of “trichosonography”, may represent a valuable technique in the evaluation of both clinical and subclinical abnormalities of the hair follicle and the innermost layers of the skin, which are otherwise inaccessible to trichoscopy. The purpose of this pictorial essay is to offer a descriptive approach to the clinical and ultrasound findings of the main hair and scalp disorders.

Keywords: Hair disorders, Sonography, Trichosonography, Cutaneous ultrasound, Dermatology, Trichology

Introduction

High-frequency ultrasound is a fast, noninvasive technique that is increasingly used in dermatology, both in the diagnosis and in the evaluation of the response to treatment, or even in surgical planning [1–5]. Its use in trichology, which is the area of dermatology that specializes in the management of hair and scalp diseases, has not yet been widely studied and widespread.

Other image modalities such as trichoscopy (magnified visualization of the hair and scalp skin) or tricogram (microscopic examination of hairs plucked from the scalp) are effective tools in the diagnosis of many of the diseases in this field. However, the main limitation of optic techniques lies in the observation of only the most superficial layers of the skin [6, 7]. Other newer techniques, such as confocal microscopy or optical coherence tomography, present the same problem and their current availability in clinics is limited [7–9].

Ultrasound can be particularly useful in trichology for the study of clinical and subclinical alterations that occur in hair and scalp diseases, both in the most superficial layers of the skin and in other deeper layers.

In this pictorial essay we detail the application of sonographic features of alopecias and other hair disorders.

Matherials and methods

We reviewed both clinical and sonographic images of the patients of our center with the diagnosis of scarring and non-scarring alopecias after histological confirmation, from 2013 to 2024. This included a total of 22 patients with androgenetic alopecia, 16 with alopecia areata, 6 with congenital triangular alopecia, 8 with trichotillomania, 7 with tinea capitis, 12 with frontal fibrosing alopecia, 8 with lichen planopilaris, 6 with discoid lupus erythematosus, 8 with folliculitis decalvans, and 6 with dissecting cellulitis. In addition, it is reviewed the ultrasound findings reported in the literature regarding these pathologies.

The equipments used were Esaote MyLab 9 with a 10–22 MHz linear probe, General Electric LOGIQ P9 with a 10–12 MHz linear probe and Clarius L20 HD3 Handheld Ultrasound (8–20 MHz linear probe). Both B-mode and Color-Doppler/Power-Doppler images were described together with literature reported sonographic features of alopecias and other hair disorders. In most ultrasound images, we provide an unedited image and a labeled image to illustrate the main findings.

Sonoanatomy of hair follicles and hair shafts

The hair follicle is a structure comprising a lower segment (mainly composed of the bulb) and an upper segment. The hair shaft is located inside the follicle and is composed of cuticle, cortex and medulla. The medulla is only present in terminal hairs (not in vellus hairs or lanugo). On ultrasound, follicles are seen as oblique hypoechoic linear structures, of 0.2–0.3 mm thickness and variable depth depending on the phase of the cycle in which they are found: in the anagen phase they reach the reticular dermis or even the hypodermis, whereas in the telogen phase they only reach the papillary dermis (Fig. 1a, b). Hair shafts are observed as hyperechoic lines of 0.05 mm thickness, and with very high frequency probes it is possible to observe a bilaminar structure (mainly in vellus hairs) (Fig. 1c) or trilaminar (in terminal hairs) (Fig. 1d) [1, 2, 10–13].

Fig. 1.

Fig. 1

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a Normal skin and hair follicles, clinical image: Appearance of healthy scalp and normal hair density. b Normal skin and hair follicles, B-mode: The epidermis is seen as a narrow hyperechoic band, the dermis as a medium echogenicity band, and the subcutaneous tissue as a hypoechoic band crossed by hyperechoic septa. Hair follicles are observed as oblique linear hypoechoic bands (yellow marked) (10–22 MHz linear probe). c Vellus hair, B mode: Hair shaft of bilaminar structure (10–22 MHz linear probe). d Terminal hair, B mode: Hair shaft of trilaminar structure (10–22 MHz linear probe)

Clinical and ultrasound characteristics of non-cicatricial alopecias

Although there are different classifications, we can divide alopecias into two main types: non-scarring alopecias and scarring alopecias. Non-scarring alopecias are characterized by the fact that hair loss is reversible, so that ultrasound will show a more or less homogeneous distribution of hair follicles. However, in more advanced cases we may observe focal areas of atrichia (absence of hair follicles).

Androgenetic alopecia

Androgenetic alopecia is the most common form of alopecia. It is mainly due to the effect of dihydrotestosterone on the hair follicle. The main clinical pattern is a loss of hair density at the frontal hairline and vertex in males, or at the medial frontoparietal region in females (Fig. 2a) [13, 14].

Fig. 2.

Fig. 2

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a Androgenetic alopecia, clinical image: Loss of capillary density in the frontoparietal midline in a woman. b Androgenetic alopecia, B-mode: Follicles of different diameters and at different depths (yellow marked), as some follicles are miniaturized and their lower segment does not reach the deep dermis (arrows) (10–22 MHz linear probe)

On ultrasound, it is possible to identify the miniaturization of follicles due to the effect of dihydrotestosterone, together with the variability conferred by anisotrichosis (95.4% in our series). Thus, we will see follicles at different levels of depth: some unaffected terminal follicles in anagen reaching the deep dermis or dermohypodermal border, mixed with other miniaturized follicles of smaller diameter and length (sometimes with ovoid morphology) reaching only the superficial dermis (Fig. 2b). However, a limitation of current ultrasound equipment lies in its failure to differentiate follicles that comprise a multifollicular unit, which subsequently affects the ability of the technique to identify androgenetic alopecia in its earliest stages, since follicular units of a single non-miniaturized follicle could be considered as normal. Late-stage follicle loss can be sometimes seen on ultrasound (36.4% in our series), and with ultra-high frequency probes, there can be observed a tendency for the shafts to be bilaminar rather than trilaminar, presumably due to the substitution of the terminal hairs with medulla by amedullary vellus hairs [1, 9, 11, 15, 16]. There are contradictory studies regarding the variation of scalp thickness, since it has been found from a lower thickness of dermis and hypodermis with respect to healthy individuals [17], to a greater thickness of subcutaneous tissue in patients with androgenetic alopecia in the frontal region, which would also correlate directly with the degree of severity [18].

Alopecia areata

Alopecia areata is a type of alopecia that occurs more frequently in children and young adults. Its etiopathogenesis is mainly autoimmune, in relation to a loss of the "immune privilege" of the hair follicle. The onset is acute, sometimes triggered by environmental factors such as stress, infections or hormonal factors. Hair loss generally occurs on one or several patches on the scalp (Fig. 3a) or in other areas (eyebrows, eyelashes, beard) [13, 14].

Fig. 3.

Fig. 3

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a Alopecia areata, clinical image: Multiple rounded, well-defined alopecia plaques. b Alopecia areata, B-mode: Widening of the follicles at their base, giving them a drop-like appearance (yellow marked), with discrete perifollicular hyperechogenicity. In advanced stages, it can be noted a decreased number of follicles (crosses) (10–22 MHz linear probe). c Alopecia areata, Color-Doppler: Widened drop-shaped follicles (yellow marked) and mild perifollicular vascularization (10–22 MHz linear probe)

Sonographically, there is a widening of the follicles, which is often more evident at the base of the follicle, giving a drop-like appearance (68.7% in our series) (Fig. 3b). This finding is related to the inflammatory infiltrate at the bulbar level that occurs in the acute phase of the disease. Occasionally, some perifollicular hyperechogenicity (25% in our series) and even a discrete increase in perifollicular vascularization on Doppler (37.5% in our series) may be observed (Fig. 3c). In advanced/chronic stages, decreased number of follicles might be detected (12.5% in our series) [1, 15, 16].

Congenital triangular alopecia

Congenital triangular alopecia is a circumscribed form of triangular or lancet-shaped alopecia (Fig. 4a), present from birth, although it is usually identified at 2–3 years of age [13, 14].

Fig. 4.

Fig. 4

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a Congenital triangular alopecia, clinical image: Asymptomatic frontotemporal lancet-shaped alopecia plaque, present from birth. b Congenital triangular alopecia, B-mode: Sharp reduction in the number of follicles (10–22 MHz linear probe)

We observed on ultrasound examination a marked reduction in the number of follicles (100% in our series) (Fig. 4b), together with some follicles of reduced thickness (83.3% in our series).

Trichotillomania

Trichotillomania is the unconscious pulling out of hairs from the scalp or other locations by the patient. Clinically, irregular and incomplete alopecic plaques with uprooted and broken hairs are observed (Fig. 5a).

Fig. 5.

Fig. 5

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a Trichotillomania, clinical image: Diffuse alopecia in eyebrows with presence of broken hairs. b Trichotillomania, B-mode: Irregularly widened follicles (yellow marked) (10–22 MHz linear probe). c Trichotheiromania, Color-Doppler: Widening of follicles (yellow marked), difusse dermal hypoechogenicity and increased vascularization (10–22 MHz linear probe)

In our experience, ultrasound may show thickened follicles (75% in our series) (Fig. 5b), and in case of trichotheiromania (rubbing or scratching of the hair and scalp) it is possible to identify some dermal hypoechogenicity and increased vascularization on Doppler (25% in our series), presumably a consequence of inflammation due to continued scratching (Fig. 5c).

Tinea capitis

Tinea capitis is an infection caused by dermatophytes, that presents clinically as one or several scaling plaques, either with or without hair loss, and with a variable degree of inflammation (Fig. 6a). In severe cases, the high intensity of inflammation can lead to an irreversible hair loss (cicatricial alopecia) [13, 14].

Fig. 6.

Fig. 6

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a Tinea capitis, clinical image: Single erythematous and scaly plaque with an exudative appearance. b Tinea capitis, Color-Doppler: Widening of the follicles (yellow marked) with increased vascularization in the dermis and hypodermis (10–22 MHz linear probe). c Highly inflammatory tinea capitis, B-mode: Confluence and fusion of widened follicles (yellow marked) (10–12 MHz linear probe). d Highly inflammatory tinea capitis, Power-Doppler: Markedly increased intralesional and perilesional vascularization (10–12 MHz linear probe) [19]

With cutaneous ultrasound, we have observed a widening of the follicles together with increased vascularization on Doppler (85.7% in our series) (Fig. 6b). In cases with severe inflammation, we can even observe an apparent fusion of the affected follicles (42.8% in our series) (Fig. 6c) with significant intralesional vascularization on Doppler (Fig. 6d) [19]. Furthermore, ultrasound can be a useful tool for the evaluation of reactive inflammatory lymphadenopathies.

Clinical and ultrasound characteristics of Cicatricial alopecias

Scarring alopecias are characterized by the presence of inflammation affecting the stem cells of the hair follicle bulge, which causes a progressive permanent loss of follicles. Thus, on ultrasound, there will be observed an inflammation of varying severity, which will mainly manifest as a hypoechogenic widening of the follicle and increased vascularization in Doppler mode. In the cicatricial phase, we will observe homogeneous dermal hyperechogenicity, increase of the interfollicular space due to loss of follicles, effacement of the dermo-hypodermal border, and a variable degree of atrophy of the scalp.

Frontal fibrosing alopecia

Frontal fibrosing alopecia is a lymphocytic cicatricial alopecia that generally appears in postmenopausal women. It is characterized by a progressive recession of the frontotemporal hairline (Fig. 7a), which may be accompanied by loss of eyebrows or hair in other locations, as well as facial papules, depression of the frontal veins, lichen planus pigmentosus, or preauricular wrinkles [13, 14, 20].

Fig. 7.

Fig. 7

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a Frontal fibrosing alopecia, clinical image: Recession of the frontotemporal hairline and depression of the facial veins. b Frontal fibrosing alopecia, Color-Doppler: Irregular thickening of the follicles (yellow marked) and a mild-moderate increase in vascularization, with areas of absence of follicles (cross) (10–22 MHz linear probe). c Frontal fibrosing alopecia, B-mode: Hyperechoic fibrous septa (arrows) located in the subcutaneous tissue (10–22 MHz linear probe)

With cutaneous ultrasound we may identify an irregular thickening of the follicles (83.3% in our series), together with a variable increase in vascularization on Doppler (75% in our series) (Fig. 7b). A non-constant (41.7% in our series) but very characteristic finding is the presence of elongated hyperechoic structures extending vertically from dermis to hypodermis (which are probably a consequence of concentric lamellar perifollicular fibrosis) (Fig. 7c). In the cicatricial phase, there is an absence of follicles [1, 11, 15, 21, 22]. It is noteworthy to comment on how ultrasound could play a relevant role in the early evaluation of subclinical signs such as perifollicular inflammation even in areas apparently clinically unaffected [23], or depression of the frontal veins resulting from dermal fibrosis, which has been identified as a potential poor prognostic factor [21]. In addition, ultrasound can be used to measure the thickness of the affected skin in comparison with healthy skin, and thus assess the degree of atrophy.

Lichen planopilaris

Lichen planopilaris is a lymphocytic cicatricial alopecia that affects middle-aged adults. The typical presentation is the onset of one or several plaques of alopecia with erythema (Fig. 8a) and pruritus or trichodynia (scalp pain), although sometimes there is only a diffuse loss of hair density with generalized erythema [13, 14, 20].

Fig. 8.

Fig. 8

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a Lichen planopilaris, clinical image: Single alopecic plaque with severe erythema. b Lichen planopilaris, B-mode: Irregularly widened follicles (yellow marked) (10–22 MHz linear probe). c Lichen planopilaris, Color-Doppler: Moderately increased perifollicular vascularization (10–22 MHz linear probe)

The ultrasound findings are similar to those of frontal fibrosing alopecia, with irregular follicular widening (75% in our series) (Fig. 8b) and increased vascularization on Doppler (87.5% in our series) (Fig. 8c), together with the absence of follicles in the cicatricial areas. However, the hyperechoic vertical lines that confer the sawtooth morphology in frontal fibrosing alopecia are not usually observed [1, 15, 22].

Discoid lupus erythematosus

Lupus erythematosus is an autoimmune disease that can present in multiple forms. Although hair loss can occur in a nonspecific pattern, the most relevant clinical presentation related to the scalp is discoid lupus erythematosus, in the form of erythematodescamative and infiltrated plaques appearing in outbreaks, generally during the seasons with the highest solar radiation (Fig. 9a) [13, 14, 20].

Fig. 9.

Fig. 9

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a Discoid lupus erythematosus, clinical image: Erythematous infiltrated alopecic plaque. b Discoid lupus erythematosus, B-mode: Dermal hypoechogenicity in relation to diffuse inflammatory infiltrate, and presence of focal thickening of the epidermis (circles) causing an acoustic shadow artifact (arrows) (10–22 MHz linear probe). c Discoid lupus erythematosus, Color-Doppler: Significant increase of vascularization in dermis and subcutaneous tissue (10–22 MHz linear probe)

Ultrasound shows findings common to other cicatricial alopecias such as irregular follicular widening (83.3% in our series) and increased vascularization on Doppler (83.3% in our series). However, it also presents characteristic findings such as diffuse dermal hypoechogenicity (66.7% in our series), which correlates with the presence of a diffuse inflammatory infiltrate and not only perifollicular, and the presence of foci of subtle epidermal thickening (50% in our series), in relation to keratotic plugs (Fig. 9b and 9c) [22].

Folliculitis decalvans

Folliculitis decalvans is typically characterized by the appearance of a one or more plaques of alopecia with significant erythema, scaling, yellowish crusts and tufted hairs (several hairs emerging from the same follicular ostium) (Fig. 10a). The course is chronic, with recurrent inflammatory exacerbations [13, 14, 20].

Fig. 10.

Fig. 10

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a Folliculitis decalvans, clinical image: Single scarring alopecic plaque with inflammatory foci and pustules in the periphery. b Folliculitis decalvans, B-mode: Severe widening of the affected follicles (yellow marked), with fusion at the base of some of them, together with absence of isolated follicles (crosses) (8–20 MHz linear probe). c Folliculitis decalvans, Power-Doppler: Significant increase in vascularization at the dermis and dermal-hypodermal border (8–20 MHz linear probe)

It is remarkable on ultrasound because of the significant follicular inflammation, which is reflected in moderate to severe follicular widening (100% in our series), sometimes even with fusion of follicles (75% in our series) (Fig. 10b), and a large increase in vascularization in the dermis that can even reach the hypodermis (87.5% in our series) (Fig. 10c) [1, 2, 10, 11].

Dissecting cellulitis

Dissecting cellulitis of the scalp is a type of predominantly neutrophilic alopecia, closely related to other follicular occlusion conditions, such as acne conglobata, hidradenitis suppurativa and pilonidal sinus. It manifests as highly inflammatory nodules, which sometimes even become fistulas, usually located on the vertex and occipital region (Fig. 11a) [13, 14, 20].

Fig. 11.

Fig. 11

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a Dissecting cellulitis, clinical image: Multiple highly inflammatory alopecic nodules in vertex and occipital region. b Dissecting cellulitis, Power-Doppler: Anechoic fluid collection (abscess) with a fragment of hair shaft inside (arrow), and marked perilesional vascularization (8–20 MHz linear probe). c Dissecting cellulitis, B-mode: Complex interconnected fistulas extending from dermis to subcutaneous tissue (yellow marked) (8–20 MHz linear probe)

The ultrasound findings are highly remarkable, and quite similar to those found in hidradenitis suppurativa. Thus, it is notable for the presence of pseudocysts (83.3% in our series), fluid collections (33.3% in our series) (Fig. 11b) and fistulas (83.3% in our series) with a significant intralesional vascularization on Doppler (Fig. 11c) [2, 10, 11, 24].

Conclusion

Trichology is a subspecialty of dermatology that has been expanding in recent years. The high impact on the quality of life of patients with hair and scalp diseases, especially those suffering cicatricial disorders, makes imperative to have techniques that allow diagnostic precision and to assess evolutionary changes that may imply a modification of the therapeutic approach. Histopathology is still today the gold standard for the diagnosis, but its invasive nature and the inherent scarring that it entails imply that its use should be reserved for cases in which there are doubts despite the prior use of other techniques. In recent years, trichoscopy has become one of the most reliable non-invasive diagnostic methods in trichology, although its limitation lies in the impossibility of accessing the deeper layers of the skin.

In this context, high-frequency ultrasound of the scalp, for which we propose the name of “trichosonography”, offers a non-invasive diagnostic alternative that allows rapid and precise evaluation of every layer of the scalp, the hair follicle and the pathological alterations occurring at such levels, especially in highly inflammatory conditions. In addition, it allows the monitoring of the activity of the disease over time and its evolution once treatment has been established, and it even offers the possibility of performing ultrasound-guided interventional procedures, such as infiltrations or biopsies.

Funding

The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.

Data availability

The data that support the findings of this manuscript are available from the corresponding author upon reasonable request.

Declarations

Conflict of Interest

The authors have no relevant financial or non-financial interests to disclose.

Ethics Approval

This study was performed according to the ethical standards of the institutional research committee and the principles of the Declaration of Helsinki of 1975.

Consent to Participate and for Publication

The patients in this manuscript have given informed consent to publication of their case details and pictures.

Footnotes

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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Data Availability Statement

The data that support the findings of this manuscript are available from the corresponding author upon reasonable request.

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