Ultrasound Feature-Based Diagnostic Model Focusing on the "Submarine Sign" for Epidermal Cysts among Superficial Soft Tissue Lesions

Ultrasound of Benign Cutaneous Tumors and Pseudotumors: The Key Lesions

Benign cutaneous tumors are commonly seen in daily practice. Most of these lesions are diagnosed based on clinical appearance, but in some cases, clinical findings are nonspecific. A diagnostic imaging exam is indicated to provide additional information, and the first choice for studying dermatologic lesions is a high-frequency color Doppler ultrasound, a noninvasive technique that can play a relevant role in all cases and give important anatomical information for final diagnosis and proper clinical management. This article aims to show the most common benign skin lesions emphasizing clinical-sonographic correlation and familiarizing radiologists with the sonographic appearance of the key benign cutaneous tumors.

Investigations on ultrasonography in the diagnosis of nodular localized cutaneous neurofibroma

OBJECTIVE

To describe the ultrasound characteristics of nodular localized cutaneous neurofibroma (NLCN).

MATERIALS AND METHODS

Clinical features and ultrasound characteristics of 43 lesions of 40 patients pathologically proven as NLCNs at Peking University Shenzhen Hospital from October 2014 to May 2022 were analyzed retrospectively. The location, length-to-thickness (L/T) ratio, thickness-to-width (T/W) ratio, shape, margin, capsule, echogenicity, echotexture, posterior features, vascularity, and "rat tail sign" were evaluated.

RESULTS

All ultrasound findings showed almost perfect agreement. More than a half of NLCNs (n = 24, 55.8%, p < 0.001) were located in the subcutaneous fat layer wholly with well-demarcation from dermis and deep fascia. Most of the NLCNs were fusiform shape (n = 27, 62.8%, p < 0.001) in the long axis and oval shape (n = 35, 81.4%, p < 0.001) in the short axis. The other ultrasound findings of NLCNs included well-defined (n = 42, 97.7%, p < 0.001), encapsulated (n = 39, 90.7%, p < 0.001), predominately hypoechoic (n = 34, 79.1%, p < 0.001), homogeneous (n = 39, 90.7%, p < 0.001), posterior enhancement (n = 29, 67.4%, p = 0.033), and avascularity (n = 37, 86.0%, p < 0.001). Only a quarter (n = 11, 25.6%, p = 0.002) of lesions were recognized with the "rat tail sign."

CONCLUSION

NLCNs present as fusiform shape in long axis and round shape in short axis. The common ultrasound findings of NLCNs are well-defined, encapsulated, predominately hypoechoic, homogeneous lesion with posterior enhancement, and poor blood supply. The "rat tail sign" has low sensitivity in NLCNs.

Integrating vascularity into the pattern classification of pilomatricomas on ultrasound provides a more competent approach for discriminative evaluation

BACKGROUND

Pilomatricoma has various manifestations on color Doppler ultrasound, and a differential diagnosis is challenging. The objective of this study was to investigate which characteristics of skin lesions on color Doppler ultrasound are effective in distinguishing pilomatricoma from epidermoid cyst and dermatofibrosarcoma protuberans.

MATERIALS AND METHODS

Records of patients with pilomatricomas (n = 63), epidermoid cysts (n = 76), and dermatofibrosarcoma protuberans (n = 19) who underwent color Doppler ultrasound evaluation and surgical excision were reviewed. The anatomical distribution and color Doppler ultrasound characteristics of these lesions were analyzed. The 63 pilomatricomas were categorized into five types based on their color Doppler ultrasound characteristics, and the roles of these five types in the differential diagnosis of the aforementioned diseases were studied.

RESULTS

Pilomatricomas, epidermoid cysts, and dermatofibrosarcoma protuberans exhibited some similar characteristics. Dominantly markedly hyperechoic or hyperechoic appearance, posterior acoustic shadowing, and the presence of vascularity were the major characteristics of pilomatricomas. The pilomatricomas could be categorized into five types, with type II having a diagnostic performance of sensitivity of 65.08%, specificity of 98.95%, area under the receiver operating characteristic curve (AUC) of 0.743, positive predictive value of 97.62%, and negative predictive value of 81.03% for the diagnosis of the aforementioned skin diseases.

CONCLUSION

A combination of dominantly markedly hyperechoic or hyperechoic appearance, posterior acoustic shadowing, and the presence of vascularity exhibits higher diagnostic performance for the differential diagnosis of pilomatricomas, epidermoid cysts, and dermatofibrosarcoma protuberans.

A comparative study of pilomatricoma and epidermoid cyst with ultrasound

AIM

To explore and compare the ultrasonic (US) features of pilomatricoma (PM) and epidermoid cyst (EC) in the differential diagnosis and improve the accuracy of US diagnosis of PM.

MATERIALS AND METHODS

Three hundred and nine patients who underwent US examination before surgery with a histopathological diagnosis of PM or EC after surgery were analysed retrospectively. The patients were categorised into the training and validation sets according to the inspection times. Univariate analysis was undertaken on the US and clinical features of PM and statistically significant variables (p<0.05) were included in the multivariate logistic regression model to establish a diagnostic model.

RESULTS

The results demonstrated that the multivariate logistic regression model for PM was statistically significant (p<0.001). The risk factors included posterior echo attenuation and hypoechoic halos (odds ratio [OR] = 9.277, 10.254) and the protective factors included age, diameter thickness, and posterior echo enhancement (OR=0.936, 0.302, 0.156). The performance of the diagnostic model was tested using the training set (area under the receiver operating characteristic curve [AUC] = 0.974, 95% confidence interval [CI] = 0.955-0.994) and the validation set (AUC = 0.967, 95% CI = 0.926-1.000), which demonstrated good discriminant ability.

CONCLUSIONS

The diagnostic accuracy for PM was higher than that for EC when the nodule is characterised by posterior echo attenuation, hypoechoic halos, smaller thickness, and younger age. The US diagnostic model developed may be used to guide the diagnosis of PM.

Ultrasonographic Spectrum of Cutaneous Cysts With Stratified Squamous Epithelium in Pediatric Dermatology: Pictorial Essay

High-resolution ultrasound (HRUS) is an important diagnostic method in dermatology, especially in pediatric population. The most common type of cutaneous cysts in children corresponds to cysts with stratified squamous epithelium (CSSE). The objective is to present the different ultrasonographic appearance of histologically proven CSSE in a retrospective review. Epidermoid, milium, trichilemmal, dermoid, and pilonidal cyst and steatocystomas are included. Utility of HRUS in diagnosis of cutaneous lesions is well established. It is important to know-and stay updated-about the wide spectrum of ultrasonographic appearance of CSSE in order to avoid misleading diagnoses.

Ultrasonographic and strain elastographic features of epidermal cyst according to body location

BACKGROUND

There are not many studies on the differences of ultrasound (US) findings between epidermal cysts (ECs) located in the trunk and those in the extremities.

PURPOSE

To compare the sonographic findings of ECs according to location in the body (trunk vs. extremity) and evaluated the feasibility of strain elastography (SE).

MATERIAL AND METHODS

This is a retrospective study of 76 patients with surgically confirmed non-ruptured EC who underwent US including SE. The US analyses included size, shape, ratio of depth to length (DLR), involvement of more than half the dermis, "submarine sign," and SE characters of each lesion. SE findings were assigned into four grades based on elasticity.

RESULTS

The submarine sign was more significantly observed in ECs located in the trunk versus extremities (P value = 0.004 and 0.035, respectively). Truncal lesions were significantly more likely to possess an ovoid shape (P < 0.05) and exhibited higher DLR (P < 0.05). There were more cases with low elasticity according to SE (grade 3 or 4) compared to high elasticity (grade 1 or 2). However, we did not observe significant differences between the two locations (P > 0.05). More-than-half signs also did not exhibit a significant difference (P > 0.05).

CONCLUSION

The submarine sign, ovoid shape, and tall lesions (higher DLR) are common in the trunk. However, the degree of elasticity and number of more-than-half signs did not differ between the two groups.

The reproducibility of shear wave and strain elastography in epidermal cyst

Purpose

This study evaluated epidermal cyst elasticity using multiple parameters of strain elastography (SE) and shear wave elastography (SWE) and assessed the reproducibility of each parameter.

Methods

This retrospective study included 73 patients with epidermal cysts who underwent SE and SWE. SE scores were classified as 1-4 according to elasticity. The strain ratio was evaluated using the elasticity ratio of lesions and adjacent subcutaneous fat tissue. For SWE, the shear wave velocity (m/s), elasticity (kPa) according to the Young modulus, velocity ratio, and elasticity ratio were evaluated. All values were measured twice. The reproducibility of SE and SWE measurements was assessed. The relationships among SE and SWE measurements were evaluated.

Results

The strain ratio on SE images showed good reproducibility (intra-class correlation coefficient [ICC]=0.789), and SE scores showed substantial reproducibility (kappa=0.753 and kappa=0.758 for readers 1 and 2, respectively). Moderate reproducibility was found for shear wave velocity and elasticity (ICC=0.750 and ICC=0.648, respectively), as well as for the shear wave velocity of the reference tissue and velocity ratio (ICC=0.747 and ICC=0.713, respectively). All SE scores were positively correlated with the strain ratio (P<0.001). The strain ratio in the second SE session was significantly correlated with the elasticity ratio and velocity ratio in the first SWE session (r=0.245, P=0.037; r=0.243, P=0.038, respectively). Other variables were not correlated.

Conclusion

SE and SWE parameters of epidermal cysts showed moderate to good reproducibility. The strain ratio on SE showed good reproducibility and could provide relatively objective and consistent measurements of epidermal cyst elasticity.

Ultrasonography of Superficial Soft-Tissue Masses: Society of Radiologists in Ultrasound Consensus Conference Statement

The Society of Radiologists in Ultrasound convened a panel of specialists from radiology, orthopedic surgery, and pathology to arrive at a consensus regarding the management of superficial soft-tissue masses imaged with US. The recommendations in this statement are based on analysis of current literature and common practice strategies. This statement reviews and illustrates the US features of common superficial soft-tissue lesions that may manifest as a soft-tissue mass and suggests guidelines for subsequent management.

Giant epidermal inclusion cyst of the axilla: a case report with diagnostic ultrasound imaging features

Epidermal inclusion cyst is a relatively common benign lesion of the skin, and it can occur anywhere in the hair-bearing area of the body. It usually appears as an asymptomatic mass, which is less than 4 cm in size. However, rarely it can occur as a large mass in the axilla, and in such cases, the location and size tend to cause more complications. The author encountered a patient with a large epidermal inclusion cyst of the axilla. Ultrasound examination showed an oval-shaped hypoechoic subcutaneous mass with dermal attachment, intralesional echogenic reflectors, filiform anechoic areas, and no vascularity. These characteristic imaging features could lead to an accurate preoperative imaging diagnosis without biopsy and avoid subsequent complications. Excision of the mass was performed due to discomfort because of the large size and growing nature of the lesion, and histological examination confirmed the diagnosis of an epidermal inclusion cyst. Therefore, recognition of diagnostic ultrasound features of this entity may enable an accurate preoperative diagnosis, even when it has an unusual size and location.

Usefulness of strain elastography in the differential diagnosis of ruptured epidermal cyst and superficial abscess

PURPOSE

The aim of this study was to evaluate the usefulness of strain elastography (SE) in the differential diagnosis of ruptured epidermal cyst and superficial abscess.

METHODS

This retrospective study included 34 patients with ruptured epidermal cysts and 17 patients with superficial abscesses who underwent ultrasonography (US) including SE. The SE characteristics were classified into four grades (1 to 4) according to elasticity. The largest length and height of the lesion and their ratio were evaluated on the US images. Involvement of more than half of the depth of the dermis and the presence of the submarine sign were assessed.

RESULTS

The inter-reader agreement of US and SE findings showed excellent or almost perfect agreement. The height, length, ratio of height to length, and more-than-half-depth sign did not significantly differ between ruptured epidermal cysts and superficial abscesses for either reader (reader 1, P=0.071, P=0.129, P=0.806, and P=0.102, respectively; reader 2, P=0.173, P=0.053, P=0.669, and P=0.060, respectively). The submarine sign was significantly more frequent in ruptured epidermal cysts than in superficial abscesses (both readers, P<0.001). The difference in SE scores between ruptured epidermal cysts and superficial abscesses, which are harder than ruptured epidermal cysts, was statistically significant (reader 1, P=0.046; reader 2, P=0.028).

CONCLUSION

The SE score and submarine sign may be useful characteristics for distinguishing ruptured epidermal cyst from superficial abscess.

Can ultrasound distinguish between dermatofibroma and subcutaneous epidermal tumors? - Imaging features and reproducibility

BACKGROUND

We evaluated ultrasound (US) features of dermatofibroma and epidermal tumor (ET). We also evaluated the reproducibility of each US findings.

MATERIALS AND METHODS

We retrospectively assessed US findings of 30 surgically confirmed dermatofibromas and 44 ETs, measuring the lesion (i.e., the depth and the length of the lesion) and calculating the depth to length ratio (DLR). We then determined the sharpness and the shape of the lesion. Finally, we assessed whether the lesion appeared with a "more-than-half sign" (involving more than 50% of the dermal layer) or a "submarine sign" (focal projection to skin). We used Pearson's chi-squared test to analyze the US findings (i.e., presence of more-than-half sign or submarine sign and margin sharpness) between dermatofibroma and ET. Inter-observer agreement of the image findings was assessed using kappa statistics.

RESULTS

The submarine sign and margin sharpness of ET lesions and the more-than-half sign and submarine sign in dermatofibroma, respectively, showed almost perfect agreement. Also, the more-than-half sign and shape of the lesion in ET and the margin sharpness and shape of the lesion in dermatofibroma showed substantial agreement. The measurements of DLRs showed excellent reproducibility. There were no significant differences of DLRs between two groups (p values = 0.512, 0.671, respectively). The more-than-half sign was observed more frequently in the context of dermatofibroma to a statistically significant degree (p < 0.001), while the submarine sign was statistically more common in relation to ET together with greater margin sharpness (p = 0.021 and <0.001, respectively).

CONCLUSIONS

More-than-half signs are common in dermatofibroma while submarine sign and sharp margin are common in ET. Each finding showed high reproducibility and can be useful as a sonographic marker for differentiation between ET and dermatofibroma.

Overview of Ultrasound Imaging Applications in Dermatology

Complete visualization of lesions is critical for the accurate diagnosis and management of dermatological diseases. Currently, the most readily available technologies used by dermatologists include dermoscopy and photography. Nevertheless, ultrasound has emerged as a useful non-invasive modality in dermatology, which can be added to the clinical examination supporting an early and more accurate diagnosis. Moreover, there are significant technological advances in recent years, such as the development of handheld devices and ultra-high frequency probes that have expanded the integration of ultrasound into daily dermatology practice. In this article, we reviewed the most common applications of ultrasound in the field of dermatology.

Ulcerated Keloid Secondary to a Coexisting Complicated Epidermal Inclusion Cyst: A Sonographic Diagnosis

Keloid is a benign fibroblastic tumor that is most often secondary to tissue injury. The clinical presentation is a hard red or purple tumor, mostly itchy or painful. The clinical objectives are to report an ulcerated keloid secondary to a central or inner complicated epidermal inclusion cyst histologically proven and to describe the sonographic findings that permitted the diagnosis. A 29-year-old man with multiple large keloids on the chest wall presented with a two-day pain history, increased volume, and ulceration on one side. Physical examination showed a keloid with edema, peripheral erythema, and a 1-cm central ulcer with purulent discharge. On the sonogram, multiple solid dermal hypodermal pseudotumors were visualized. The lesions were well-defined hypoechogenic heterogeneous solid masses that were hypovascular with color Doppler, concordant with keloids. Within the ulcerated enlarged mass, a complicated epidermal inclusion cyst was discovered with inflammatory changes. The significance of this case lies in the very low frequency of ulceration of a keloid and the high diagnostic value of sonography to demonstrate the presence of a coexisting epidermal inclusion cyst. In the differential diagnosis of an ulcerated keloid, sonography can assist in achieving a better presurgical approach.