Differences in Sonographic Features of Ruptured and Unruptured

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1 ORIGINAL RESEARCH Differences in Sonographic Features of Ruptured and Unruptured Epidermal Cysts Wei-Hsin Yuan, MD, Hui-Chen Hsu, MD, Yi-Chen Lai, MD, Yi-Hong Chou, MD, Anna Fen-Yau Li, MD, PhD Received December 23, 2010, from the Division of Radiology, Taipei Municipal Gan-Dau Hospital Taipei Veterans General Hospital, Taipei, Taiwan (W.-H.Y., Y.-C.L., Y.-H.C.); Departments of Radiology (W.-H.Y., Y.-C.L., Y.-H.C.) and Pathology (A.F.-Y.L.), Taipei Veterans General Hospital and National Yang Ming University, Taipei, Taiwan; and Department of Medical Imaging, Taiwan Adventist Hospital, Taipei, Taiwan (H.-C.H.). Revision requested January 20, Revised manuscript accepted for publication September 1, We thank Chih-Ping Chiu, senior research assistant, for assistance in preparation of this article. Address correspondence to Yi-Hong Chou, MD, Department of Radiology, Taipei Veterans General Hospital, No. 201, Section 2, Shih-Pai Rd, Taipei, Taiwan. Objectives This study aimed to report the differences in sonographic features of ruptured and unruptured epidermal cysts. Methods We reviewed and analyzed the sonographic features of superficial epidermal cysts of in 2 subgroups of 46 patients: 20 with ruptured cysts and 26 with unruptured cysts. All lesions were diagnosed either by excisional biopsy or by debridement biopsy. Sonographic features used in the analysis included tumor size, location, echo texture, pericystic changes, boundary, and shape on gray scale sonography and lesion vascularity on color Doppler sonography. Pathologic examinations were reviewed with emphasis on differences between ruptured and unruptured epidermal cysts. Results Unruptured epidermal cysts showed significantly higher frequencies of an oval shape, presence of a halo, well-circumscribed boundaries, and lack of blood flow signals (P <.05). In contrast, ruptured cysts usually had a lobulated shape, a slightly poorly defined or poorly defined boundary, the absence of a halo, and intermediate grades of lesion vascularity. The lesion sizes and sonographic features, including dermal attachment, a hypoechoic echo texture, posterior acoustic enhancement, and the presence of intralesional hyperechoic strips and hypoechoic debris, showed no significant differences between the groups (P >.05). In pathologic studies, acute and chronic inflammatory reactions, more prominent microvessels, and abscess formation in the adjacent stromal tissue, the lesions, or both could be detected in the 20 ruptured epidermal cysts but not in the unruptured cysts. Conclusions This research shows that recognition of different sonographic features is helpful for differentiating ruptured and unruptured epidermal cysts. Key Words color Doppler sonography; ruptured epidermal cyst; sonography; unruptured epidermal cyst E pidermal cysts are the most common superficial epithelial cysts. 1 5 The cysts are benign cutaneous or subcutaneous lesions, which are lined with stratified squamous epithelium and filled with keratin debris. 3 7 These lesions often arise in the hairbearing areas of the body, 1,3 5 including the scalp, face, neck, trunk, and back. Fewer than 10% of epidermal cysts occur on the extremities, palms, soles, and breasts. Obstruction of hair follicles results in the formation of epidermal cysts. 8 Those cysts occurring in the nonfollicular areas of the body are thought to be due to traumatic or surgical implantation of the epidermis into the dermis or subcutis. 1,9 Palmoplantar epidermal cysts may develop when infected by human papillomavirus 57 or by the American Institute of Ultrasound in Medicine J Ultrasound Med 2012; 31:

2 Identification of unruptured and ruptured cysts is important for treatment decisions. Most epidermal cysts are harmless, and malignant transformation of epidermal cysts is uncommon. 2,9 However, on palpation, unruptured epidermal cysts can mimic other subcutaneous cystic masses, solid tumors, or vascular lesions. 9 Similarly, ruptured epidermal cysts can lead to inflammation and abscess formation and can even resemble malignant soft tissue tumors. 5,7,9 Although asymptomatic unruptured epidermal cysts need no treatment, ruptured or infected epidermal cysts should be surgically removed because they can be erythematous, swollen, and painful and may recur after simple antibiotic treatment. 5,11 Sonography has been widely used in the evaluation of superficial lesions. The lack of definitive differences in sonographic findings for ruptured and unruptured epidermal cysts may lead to unnecessary sonographically guided needle biopsy and surgical intervention for epidermal cysts. To the best of our knowledge, only limited reports have been published on the differences in sonographic findings of ruptured and unruptured epidermal cysts in superficial soft tissue. 2,5,6 The purpose of this retrospective study was to analyze the differences in the gray scale and color Doppler sonographic findings of ruptured and unruptured epidermal cysts with emphasis on the echo texture, pericystic changes, shape, boundary, and lesion vascularity. Materials and Methods The surgical pathology database at our hospital was searched for cases using the index terms epidermal cyst and epidermal inclusion cyst from January 2004 to January There were, in total, 594 patients whose lesions had been pathologically diagnosed as epidermal cysts or epidermal inclusion cysts. Only 46 of the 594 patients underwent presurgical sonography and were included in this study. The other 548 patients who underwent surgery without sonography were excluded. The abstractor (Chih- Ping Chiu, senior research assistant), who was blinded to the study hypothesis, did the abstraction. This study was approved by our Institutional Review Board, and informed patient consent was not required because of the retrospective nature of the study. All 46 patients underwent sonography for characterization of the mass and then underwent surgical excision within 1 week to 1 month. Debridement biopsy was performed in 2 ruptured epidermal cysts, and excisional biopsy was performed in the other 44 lesions. The study population consisted of 15 female patients and 31 male patients with an overall mean age of 47.8 years (range, 3 85 years). Among these patients, 20 had ruptured epidermal cysts, including 8 female patients and 12 male patients with a mean age of 45.6 years (range, years). Twenty-six patients had unruptured cysts, including 7 female patients and 19 male patients with a mean age of 49.5 years (range, 3 85 years). Routine gray scale and color Doppler sonographic examinations of the clinically palpable lesions were performed using real-time scanners (HDI 5000 and HDI 3000; Philips Healthcare, Bothell, WA; and LOGIQ 9; GE Healthcare, Milwaukee, WI) equipped with high-resolution linear probes (L12 5 MHz). When a lesion was detected on gray scale sonography, color Doppler sonography was performed with the proper settings. The Doppler gain setting was adjusted to a level associated with minimal noise. Flow toward the transducer was displayed in red and flow away from the transducer in blue. Without the knowledge of the nature of the epidermal cyst, gray scale and color Doppler sonography were performed in transverse and longitudinal planes for each lesion. The blood flow in each lesion was measured on color Doppler sonography for the lesion as a whole and for perilesional areas. In this small retrospective study, we assessed epidermal cysts with sonography and biopsy on the basis of independent reviews by 2 radiologists and 1 pathologist. All sonographic studies were analyzed retrospectively by 2 experienced radiologists (H.-C.H., with 15 years of experience, and Y.-C.L., with 10 years of experience). Two radiologists, blinded to the biopsy results, evaluated the sonograms together on a picture archiving and communication system monitor, and all interpretations were decided by consensus and recorded. The analysis included the lesion size and location on sonography, the sonographic features (ie, echo texture, pericystic changes, shape, and boundary), and grading and the distribution of color flow signals representing lesion vascularity on color Doppler sonography. The image with maximum blood flow signals for each lesion on color Doppler sonography was recorded for comparison. Using simple descriptive statistics, the lesion size was divided into 9 groups according to maximum diameter shown on sonography: less than 10.0, 10.0 to 19.9, 20.0 to 29.9, 30.0 to 39.9, 40.0 to 49.9, 50.0 to 59.9, 60.0 to 69.9, 70.0 to 79.9, and 80.0 to 89.9 mm. The lesion location was marked by the body part and skin layer where the lesion was identified on sonography. 3,12,13 The echo texture of each lesion was characterized by echogenicity and homogeneity. Echogenicity was classified as hypoechoic, isoechoic, or hyperechoic with respect to the background of the dermis layer of normal skin. Homogeneity was categorized as homogeneous, slightly heterogeneous, or heterogeneous. 266 J Ultrasound Med 2012; 31:

3 Lesions with areas of slightly increased or decreased echogenicity compared with the greater portion of the lesion were defined as slightly heterogeneous. When a lesion showed areas of apparently increased or decreased echogenicity, it was described as having a heterogeneous echo texture. Posterior acoustic features of the lesions were also evaluated. A halo was defined as a sharply demarcated hypoechoic or hyperechoic rim surrounding a lesion and separating it from adjacent tissue. The shape of a lesion was classified as round, oval, lobulated, or irregular. The boundary of a lesion was classified as well circumscribed if the lesion s contour from normal cutaneous or subcutaneous tissue was clear for greater than 90% of the lesion 14 or poorly defined when the contour from the normal cutaneous or subcutaneous tissue was unclear for greater than 50% of the lesion; otherwise, it was defined as slightly poorly defined, ie, unclear boundary for 10% to 50% of the lesion. Lesion vascularity reviewed on color Doppler sonography was subjectively graded on a 4-step analog scale of 0 to +++ as follows 15 : 0 for no detectable color signal; + for transient occasional pixels of color or the presence of a single color flow signal in or around the lesion; ++ for multiple pixels of color or multiple pedicles of blood supply or the presence of well-defined vessels in or around the lesion; and +++ for large feeding vessels and a high number of color signals in or around the lesion. The distribution of color flow signals was divided into a peripheral, central, or mixed type according to the appearance of the blood flow in or around the lesion. With a small number of patients in each group for comparison, the study applied nonparametric tests (Mann- Whitney U test) for continuous variables and the χ 2 or Fisher exact test for categorical variables to assess differences between characteristics in the subgroups. The significance level was set at P <.05. One experienced pathologist (A.F.-Y.L.) with 20 years of experience, without knowledge of the sonographic findings, retrospectively reviewed microscopic slides from the 46 patients. The pathologic examination focused on the composition of the epidermal cysts and the difference between ruptured and unruptured cysts. After the sonographic and pathologic examinations, a radiologist (W.- H.Y., with 12 years of experience in medical sonography) integrated the reviewed records of the sonographic and pathologic findings for synthesis. Results Tables 1 4 summarize the sonographic appearances of the ruptured and unruptured epidermal cysts. The study Table 1. Locations of Ruptured (n = 20) and Unruptured (n = 26) Epidermal Cysts Ruptured, Unruptured, Total, Location n (%) n (%) n (%) Axilla 2 (10.0) 0 2 (4.3) Back 3 (15.0) 1 (3.8) 4 (8.7) Breast 6 (30.0) 2 (7.7) 8 (17.4) Buttock 3 (15.0) 2 (7.7) 5 (10.9) Finger 4 (20.0) 8 (30.8) 12 (26.1) Knee 1 (5.0) 1 (3.8) 2 (4.3) Neck 1 (5.0) 3 (11.5) 4 (8.7) Toe 0 1 (3.8) 1 (2.2) Elbow 0 2 (7.7) 2 (4.3) Popliteal 0 1 (3.8) 1 (2.2) Palm 0 2 (7.7) 2 (4.3) Eyelid 0 1 (3.8) 1 (2.2) Plantar 0 1 (3.8) 1 (2.2) Coccyx 0 1 (3.8) 1 (2.2) showed breasts and fingers as the 2 most common locations of ruptured cysts and fingers and necks as the 2 most common locations of unruptured cysts (Table 1). Only 1 ruptured cyst was found above the deep layer of the dermis (Figure 1). The other 45 of 46 lesions (97.8%) appeared in the junction of the dermis and the subcutaneous region or dermal attachment (just beneath the deep layer of the dermis; Figures 2, 3, 4A, 5, 6A, and 7A). 3,12,13 The sizes of the ruptured and unruptured epidermal cysts ranged from 8.9 to 82.4 mm (mean, 24.8 mm; Table 2) and 8.5 to 81.0 mm (mean, 26.8 mm; Table 2), respectively. The difference in the mean sizes of the lesions between the groups was not statistically significant (P =.438, Mann-Whitney U test). The 2 most common size ranges were 10.0 to 19.9 and 20.0 to 29.9 mm in both ruptured and unruptured cysts. Table 2. Maximum Diameters of Ruptured (n = 20) and Unruptured (n = 26) Epidermal Cysts on Gray Scale Sonography Diameter, Ruptured, Unruptured, Total, mm n (%) n (%) n (%) < (15.0) 2 (7.7) 5 (10.9) (40.0) 10 (38.5) 18 (39.1) (20.0) 6 (23.1) 10 (21.7) (15.0) 2 (7.7) 5 (10.9) (15.4) 4 (8.7) (3.8) 1 (2.2) (5.0) 0 1 (2.2) (0) (5.0) 1 (3.8) 2 (4.3) J Ultrasound Med 2012; 31:

4 In Table 3, the homogeneity features, including a heterogeneous echo texture (Figures 1 and 2), a slightly heterogeneous echo texture (Figure 3), and a homogeneous echo texture (Figure 4A), showed a nonsignificant difference between the ruptured and unruptured epidermal cysts (P =.270). Differences in echogenicity, the presence of posterior acoustic enhancement (Figures 2, 4A, 5, 6A, and 7A), hypoechoic debris (Figure 2), and hyperechoic strips (Figure 3) between the groups was also not statistically significant (P >.05). The halos of epidermal cysts vary in thickness on sonography. The maximum thickness of the halos was about 3 mm. Halos were found in 5 ruptured cysts (25%, 4 hypoechoic and 1 hyperechoic) and 16 unruptured cysts (61.5%, 11 hypoechoic and 5 hyperechoic; P =.043; Figures 2 and 4A). The differences in boundaries and shapes, including oval (Figure 2), round, and lobulated features (Figures 4A and 5), were significant between the groups (P <.001). Table 3. Gray Scale Sonographic Features of Ruptured (n = 20) and Unruptured (n = 26) Epidermal Cysts Feature Ruptured Unruptured P Echogenicity, n (%) Hypoechoic 18 (90.0) 23 (88.5) >.99 a Isoechoic 2 (10.0) 3 (11.5) Homogeneity, n (%) Homogeneous 7 (35.0) 15 (57.7).270 a Heterogeneous 6 (30.0) 4 (15.4) Slightly heterogeneous 7 (35.0) 7 (26.9) Posterior acoustic feature, n (%) Enhancement 14 (70.0) 20 (76.9).717 a Shadowing 0 1 (3.8) Absent 6 (30.0) 5 (19.2) Hypoechoic debris, n (%) Presence 6 (30.0) 12 (46.2).266 b Absence 14 (70.0) 14 (53.8) Hyperechoic strips, n (%) Presence 12 (60.0) 21 (80.8).12 b Absence 8 (40.0) 5 (19.2) Halo, n (%) Hypoechoic halo 4 (20.0) 11 (42.3).043 a Hyperechoic halo 1 (5.0) 5 (19.2) Absent 15 (75.0) 10 (38.5) Shape, n (%) Round 1 (5.0) 3 (11.5) <.001 a Oval 6 (30.0) 20 (76.9) Lobulated 13 (65.0) 3 (11.5) Boundary, n (%) Well circumscribed 4 (20) 20 (76.9) <.001 a Slightly poorly defined 11 (55) 3 (11.5) Poorly defined 5 (25) 3 (11.5) Table 4. Color Doppler Sonographic Features of Ruptured (n = 20) and Unruptured (n = 26) Epidermal Cysts Feature Ruptured Unruptured P a Flow distribution, n (%) Peripheral 7 (35.0) 3 (11.5) <.001 Central 1 (5.0) 1 (3.8) Mixed 6 (30.0) 0 No blood flow 6 (30.0) 22 (84.6) Flow vascularity, n (%) Grade 0 6 (30.0) 22 (84.6) <.001 Grade + 7 (35.0) 4 (15.4) Grade ++ 7 (35.0) 0 a Fisher exact test. Table 4 shows that the difference in blood flow distribution on color Doppler sonography was statistically significant between the groups (P <.001). Blood flow patterns included no blood flow (Figure 5), a peripheral pattern (Figure 6A), a central pattern, and a mixed pattern (Figure 7A). Central color flow was detected in 1 ruptured epidermal cyst (5%) and 1 unruptured cyst (3.8%). Moreover, 14 ruptured cysts with color flow signals showed intermediate (+ and ++) grades of vascularity (Figures 6A and 7A), but 4 epidermal cysts with color flow signals had only grade + vascularity (P <.001). Microscopic examinations showed that the walls of the 46 epidermal cysts were composed of variable amounts Figure 1. Ruptured epidermal cyst in the upper inner quadrant of the right breast of a 68-year-old woman. Longitudinal sonography shows a heterogeneously hypoechoic lesion (short arrow). The lesion appears superficial to the deep dermal layer. D indicates dermis; and H, hypodermis (subcutaneous tissue). a Fisher exact test. b χ 2 test. 268 J Ultrasound Med 2012; 31:

5 of keratinizing stratified squamous epithelium (Figures 4, B and C, and 6B). The 26 unruptured cysts had much more complete walls than did the 20 ruptured cysts. Most of the cyst contents in the 46 cases were lost during surgical and pathologic processes (Figure 4B). Variable amounts of keratinous debris or keratin material arranged in dense or scattered laminated layers could be preserved in the cysts (Figures 4C and 6B). Desquamative cellular lipid or protein fragments also could be seen in the some cysts. In the 20 ruptured cysts, photomicrography showed granulation tissue, acute and chronic inflammatory cell infiltration, a few multinucleate foreign body giant cells or abscess formation, and more prominent microvessels in the adjacent stromal tissue, in the ruptured cysts, or both (Figures 6B and 7B); however, none of these microscopic findings could be identified in the unruptured cysts. There was no evidence of malignancy in any specimen examined. Discussion Forty-five of 46 lesions in our study (97.8%) appeared in the junction of the dermis and the subcutaneous region or dermal attachment. An epidermal cysts, the most common benign subcutaneous epithelial cyst found on clinical examination, 1,6 should be the first diagnosis suspected when a lesion appears in the junction of the dermis and subcutaneous layers. 3,7 Other common skin lesions that can be found in the same location (junction of the dermis and subcutaneous tissue), such as pilomatrixomas, should also be considered in the differential diagnosis. 16 Pilomatrixomas may present as totally or partially calcified nodules, as intrinsic microcalcifications, or as cystic variants (among their sonographic patterns), which could help differentiate epidermal cysts from pilomatrixomas. 17 Epidermal cysts contain variable amounts and varied arrangements of keratin debris. 2,7 Sonographic findings of internal compact laminae of keratin might show an onion skin appearance, a target appearance, or a laminated appearance. 3,18 Scattered fragments of packed lamellae of keratin might appear as a hypoechoic or hyperechoic echo texture with nodular, linear, or branching structures on sonography. 11,18,19 Hyperechoic strips might be correlated with dense keratin debris, whereas hypoechoic debris might be correlated with lipid fragments or keratin fragments containing additional water. 18 These two specific sonographic features indicating the presence of keratin debris could be used to distinguish epidermal cysts from other superficial tumors such as synovial cysts, ganglions, sebaceous cysts, pilomatrixomas, fibromas, lipomas, galactoceles, and xanthomas. 1,2,9,11,16,17 Figure 3. Ruptured epidermal cyst in the left buttock of a 52-year-old man. Transverse sonography shows a slightly heterogeneously hypo - echoic mass with dermal attachment. The inner contents show many short hyperechoic strips (short arrows). D indicates dermis; E, epidermis; and H, hypodermis (subcutaneous tissue). Figure 2. Unruptured epidermal cyst in the right side of the neck of a 73- year-old man. Transverse sonography shows a heterogeneously hypoechoic well-circumscribed oval mass with a hyperechoic halo (curved arrow). Posterior acoustic enhancement (asterisk) and dermal attachment are also shown. Inner contents show the typical numerous areas of hypoechoic debris (short arrows). D indicates dermis; and H, hypodermis (subcutaneous tissue). J Ultrasound Med 2012; 31:

6 In our study, homogeneous or heterogeneous hypo - echoic internal echoes, intralesional hypoechoic debris, hyperechoic strips, and posterior acoustic enhancement were common features in both the ruptured and unruptured epidermal cysts. These findings agree with several previous studies on epidermal cysts. 6,20,21 The ruptured epidermal cysts showed a slightly heterogeneous or heterogeneous echo texture more frequently than did the unruptured cysts (65.0% versus 42.3%), which might have been due to inflammatory cell infiltration, granulation tissue, or an abscess component in or around the ruptured cysts. The halo on sonography showed a sharply demarcated hypoechoic or hyperechoic rim surrounding the epidermal cyst. The hypoechoic halo of ruptured and unruptured epidermal cysts might represent the more complete walls of cysts composed of keratinizing stratified squamous epithelium, 3,5,18 and the hyperechoic halo might represent posterior acoustic enhancement. Ruptured epidermal cysts tend to have fragmentation of the cystic walls and leakage of nonresorbable keratin. If the fragmented wall of a ruptured epidermal cyst is involved with an inflammatory reaction or granulation tissue caused by irritation from keratin leakage, 1 3,5,22 the sharpness and continuity of the walls would disappear on pathologic examination, and the hypoechoic and hyperechoic halos would be absent on sonography. Previous investigators reported that lobulations from ruptured epidermal cysts and the presence of combined protruding portions from unruptured ones were the important differences in the sonographic findings of the two types. 2,3,5 Our results emphasized a higher frequency of the absence of a halo in the ruptured cysts than in the unruptured cysts (P =.043). According to the pathologic examinations in our study, the prominent microvessels in the surrounding granulation tissue and in the ruptured epidermal cysts could explain the finding that ruptured cysts had a significantly A Figure 4. Unruptured epidermal cyst in the plantar aspect of the left foot of a 41-year-old woman. A, Transverse sonography shows a homogeneously isoechoic lobulated mass. A hypoechoic halo (curved arrow), posterior acoustic enhancement (asterisk), and hyperechoic strips (short arrows) are shown. D indicates dermis; and H, hypodermis (subcutaneous tissue). B, Pathologic specimen shows that partial defects (arrows) in the cyst wall are cutting artifacts during slide preparation due to its thin wall. Most cystic contents are lost during pathologic processes (hematoxylin-eosin, original magnification 1). C, Pathologic specimen shows the unruptured epidermal cyst with a wall composed of stratified squamous epithelium (long arrows). Scattered keratinous debris (curved arrows) and some keratin material arranged in laminated layers in the cyst (short arrows) are present (hematoxylin-eosin, original magnification 100). B C 270 J Ultrasound Med 2012; 31:

7 higher frequency of mixed and central blood flow signals on color Doppler sonography than did the unruptured ones (P <.001), which is consistent with previous studies. 1,2 In 1 unruptured epidermal cyst (representing 3.8% of the total), the positive central color flow signals could have been due to motion artifacts that were misinterpreted as real signals; no microvessels were noted on the histopathologic studies of the unruptured cysts. Lack of blood flow signals in unruptured epidermal cysts on color Doppler sonography could be helpful for differentiating unruptured from ruptured cysts and other superficial solid tumors. 23 This study had several limitations. First, it was a retrospective study of a relatively small series, which might be insufficient for representing the variety of ruptured and unruptured epidermal cysts. Second, the internal composition including keratin debris in the cysts had been washed out during surgical and pathologic processes. It was therefore difficult to correlate the sonographic features with the distribution of keratin particles. Third, interobserver variability was not considered because of the retrospective nature and methodological limitations of the study. Fourth, other superficial soft tissue masses were not included for comparison. Last, a correlation was not considered between the sonographic features and clinical histories of the ruptured and unruptured cysts, including onset, duration, and symptoms, and signs. In conclusion, unruptured epidermal cysts are more likely than ruptured cysts to have an oval shape, a wellcircumscribed boundary, a halo on gray-scale sonography, and lack of blood flow signals on color Doppler sonography. In contrast, sonographic features including a lobulated shape, a slightly poorly defined or poorly defined boundary, the absence of a halo, and the presence of intermediate grades of vascularity are more indicative of ruptured epidermal cysts. Recognition of the differences in the sonographic features of ruptured and unruptured epidermal cysts could provide evidence to support a correct diagnosis. Figure 6. Ruptured epidermal cyst in the lower right side of the back of a 66-year-old man. A, Longitudinal color Doppler sonography shows a predominantly well-circumscribed heterogeneously hypoechoic lobulated mass. The color Doppler pattern is predominantly marginal or peripheral in distribution. Lesion vascularity was graded +. Asterisk indicates posterior acoustic enhancement; D, dermis; E, epidermis; and H, hypodermis (subcutaneous tissue). B, Pathologic specimen shows a ruptured cyst with an incomplete wall composed of keratinizing squamous epithelium (long white arrow). Keratin material arranged in laminated layers is shown in the cyst (short white arrow). The ruptured cyst releases keratin material (asterisk) as an irritant, which causes inflammatory reactions (thick white arrow) and dilatation of microvessels (black arrows) in the adjacent stromal tissue (hematoxylin-eosin, original magnification 100). A Figure 5. Ruptured epidermal cyst in the upper right side of the back of a 72-year-old man. Longitudinal color Doppler sonography shows a heterogeneously hypoechoic lobulated mass (arrow) with a poorly defined boundary. No blood flow signal is evident in or around the lesion. Lesion vascularity was graded 0. Asterisk indicates posterior acoustic enhancement; D, dermis; and H, hypodermis (subcutaneous tissue). B J Ultrasound Med 2012; 31:

8 A B Figure 7. Ruptured epidermal cyst in the right buttock of a 24-year-old man. A, Longitudinal color Doppler sonography shows a heterogeneously hypoechoic oval mass. Mixed blood flow signals are shown in and around the lesion. Lesion vascularity was graded ++. Asterisk indicates posterior acoustic enhancement; D, dermis; E, epidermis; and H, hypodermis (subcutaneous tissue). B, Pathologic specimen shows keratinous debris (long arrows), prominent inflammatory reactions, multinucleated giant cells (curved arrows), and multiple microvessels (short arrows) in and around the cystic lesion (hematoxylin-eosin, original magnification 200). References 1. Fisher AR, Mason PH, Wagenhals KS. Ruptured plantar epidermal inclusion cyst. AJR Am J Roentgenol 1998; 171: Lee HS, Joo KB, Song HT, et al. Relationship between sonographic and pathologic findings in epidermal inclusion cysts. J Clin Ultrasound 2001; 29: Huang CC, Ko SF, Huang HY, et al. Epidermal cysts in the superficial soft tissue: sonographic features with an emphasis on the pseudotestis pattern. J Ultrasound Med 2011; 30: Kim HK, Kim SM, Lee SH, Racadio JM, Shin MJ. Subcutaneous epidermal inclusion cysts: ultrasound (US) and MR imaging findings. Skeletal Radiol 2011; 40: Jin W, Ryu KN, Kim GY, Kim HC, Lee JH, Park JS. Sonographic findings of ruptured epidermal inclusion cysts in superficial soft tissue: emphasis on shapes, pericystic changes, and pericystic vascularity. J Ultrasound Med 2008; 27: Denison CM, Ward VL, Lester SC, et al. Epidermal inclusion cysts of the breast: three lesions with calcifications. Radiology 1997; 204: Kwak JY, Park HL, Kim JY, et al. Imaging findings in a case of epidermal inclusion cyst arising within the breast parenchyma. J Clin Ultrasound 2004; 32: Taira N, Aogi K, Ohsumi S, Takashima S, Kawamura S, Nishimura R. Epidermal inclusion cyst of the breast. Breast Cancer 2007; 14: Hong SH, Chung HW, Choi JY, Koh YH, Choi JA, Kang HS. MRI findings of subcutaneous epidermal cysts: emphasis on the presence of rupture. AJR Am J Roentgenol 2006; 186: Lee S, Lee W, Chung S, et al. Detection of human papillomavirus 60 in epidermal cysts of nonpalmoplantar location. Am J Dermatopathol 2003; 25: Whang IY, Cho HJ, Lee SL, Jung NY, Chun KA, Kim KT. Epidermoid cyst appearing as a malignancy-mimicking subcutaneous lesion on ultrasonography. J Med Ultrasonics 2009; 36: El Gammal S, El Gammal C, Kaspar K, et al. Sonography of the skin at 100 MHz enables in vivo visualization of stratum corneum and viable epidermis in palmar skin and psoriatic plaques. J Invest Dermatol 1999; 113: Fornage BD. High-frequency sonography of the skin. Eur J Radiol 1995; 2: Yuan WH, Hsu HC, Chou YH, Hsueh HC, Tseng TK, Tiu CM. Gray-scale and color Doppler ultrasonographic features of pleomorphic adenoma and Warthin s tumor in major salivary glands. Clin Imaging 2009; 33: Martinoli C, Derchi LE, Solbiati L, Rizzatto G, Silvestri E, Giannoni M. Color Doppler sonography of salivary glands. AJR Am J Roentgenol 1994; 163: Hassanein AH, Alomari AI, Schmidt BA, Greene AK. Pilomatrixoma imitating infantile hemangioma. J Craniofac Surg 2011; 22: Solivetti FM, Elia F, Drusco A, Panetta C, Amantea A, Di Carlo A. Epithelioma of Malherbe: new ultrasound patterns. J Exp Clin Cancer Res 2010; 6: Cho JH, Chang JC, Park BH, Lee JG, Son CH. Sonographic and MR imaging findings of testicular epidermoid cysts. AJR Am J Roentgenol 2002; 178: Stein MM, Stein MW, Cohen BC, Li M, Koenigsberg M. Unusual sonographic appearance of an epidermoid cyst of the testis. J Ultrasound Med 1999; 18: Fajardo LL, Bessen SC. Epidermal inclusion cyst after reduction mammoplasty. Radiology 1993; 186: Yasumoto M, Shibuya H, Gomi N, Kasuga T. Ultrasonographic appearance of dermoid and epidermoid cysts in the head and neck. J Clin Ultrasound 1991; 19: Whang IY, Lee J, Kim JS, Kim KT, Shin OR. Ruptured epidermal inclusion cysts in the subareolar area: sonographic findings in two cases. Korean J Radiol 2007; 8: Ma LD, McCarthy EF, Bluemke DA, Frassica FJ. Differentiation of benign from malignant musculoskeletal lesions using MR imaging: pitfalls in MR evaluation of lesions with a cystic appearance. AJR Am J Roentgenol 1998; 170: J Ultrasound Med 2012; 31: