MRI features of nipple leiomyoma in a male patient: A case report

Abstract

Nipple leiomyoma is a benign cutaneous tumor that arises from the smooth muscle fibers of the musculus areolae and represents the rarest subtype of cutaneous leiomyoma. Since its first description by Virchow in 1854, approximately 50 cases have been reported, with only 20 involving male patients. Imaging findings, particularly the MRI characteristics, have been insufficiently documented. We report a man in his 70s with a 10-year history of left nipple pain. Ultrasonography revealed a mildly irregular hypoechoic mass with increased vascularity. MRI demonstrated a well-defined, smoothly marginated mass with intermediate signal intensity on STIR and T1WI, a hypointense rim, and a slow, persistent contrast-enhancement pattern without diffusion restriction. Core needle biopsy confirmed a leiomyoma. The lesion was managed conservatively at the patient’s request. Recognition of the MRI characteristics of nipple leiomyoma may help the differential diagnosis of nipple lesions.

Introduction

Nipple leiomyomas are extremely rare benign tumors and are one of the least common subtypes of cutaneous leiomyomas [1,2]. Cutaneous leiomyomas are benign tumors and originate from smooth muscle cells, and are classified into 3 subtypes based on their site of origin: pilar leiomyoma, arising from the arrector pili muscle; angioleiomyoma, arising from the tunica media of blood vessels; and genital leiomyoma, arising from smooth muscle in the genital region, including the scrotum, the nipple/areola, and the vulva [1]. Among these, genital leiomyomas are uncommon and nipple leiomyomas are considered the rarest [1,2]. Since the first report by Virchow in 1854, approximately 50 cases have been reported. However, cases in male patients are particularly rare, with only 22 cases identified in a 2023 review [2].

Imaging findings, particularly MRI features, have rarely been described. To date, the literature reports only 1 case involving a female patient [3]. Therefore, the imaging characteristics of nipple leiomyoma remain poorly understood. Here, we present the imaging findings of a nipple leiomyoma in a male patient and discuss them in the context of the existing literature.

Case report

A man in his 70s had experienced pain in his left nipple for approximately 10 years. Eight years earlier, owing to worsening pain, he presented to the Department of Plastic Surgery at our hospital. A skin infection was initially suspected and oral antibiotics were prescribed; however, his symptoms persisted. He was then referred to the Department of Breast Surgery, where a skin biopsy was performed and a diagnosis of nipple leiomyoma was made. Since then, symptomatic treatment with topical corticosteroids has been administered intermittently for several years during episodes of pain. Because of the recent exacerbation of symptoms, MRI was performed to further evaluate the lesion. He had no significant medical history, was not taking any medications, and had no family history of breast cancer.

Physical examination revealed bilateral gynecomastia and a firm, elastic mass in the left nipple (Fig. 1). Mammography confirmed bilateral gynecomastia; however, the nipple lesion was not clearly visualized (Fig. 2A). Ultrasonography revealed a mildly irregular, hypoechoic mass with posterior acoustic enhancement, measuring approximately 0.95 cm, just beneath the left nipple (Fig. 2B). Doppler ultrasonography of the left nipple mass revealed increased internal blood flow in the lesion (Fig. 2C).

Fig. 1.

Gynecomastia was observed in the left breast, with no visible abnormalities of the nipple on inspection. On palpation, a firm lesion was detected just beneath the nipple.

Fig. 2.

The nipple lesion was not clearly visualized on mammography (A). Ultrasonography on transverse view showed a mildly irregular, hypoechoic mass measuring approximately 0.95 cm just beneath the left nipple, with posterior acoustic enhancement (B). Color Doppler ultrasonography on transverse view demonstrated increased peripheral vascularity within the mass (C).

MRI revealed a well-defined, smoothly marginated mass in the left nipple. Correspoding images of the right breast (Fig. 3A, C, E, G) showed no abnormal findings. On short tau inversion recovery (STIR) images, the lesion showed intermediate signal intensity with a hypointense rim (Fig. 3B). On T1-weighted images (T1WI), the mass was slightly hypointense compared with the adjacent muscle (Fig. 3D). The lesion was not clearly visualized on diffusion-weighted imaging (DWI) and there was no evidence of significant diffusion restriction (Fig. 3F, H). Dynamic contrast-enhanced T1WI demonstrated a slow and persistent enhancement pattern with mild heterogeneous internal enhancement (Fig. 4, Fig. 5). MRI was performed on a 3.0-T scanner using a dedicated breast coil. The slice thickness was 4 mm for STIR, T1-weighted imaging, and diffusion-weighted imaging, and 1 mm for dynamic contrast-enhanced sequences. Diffusion-weighted imaging was obtained with b values of 0 and 1000 s/mm². Dynamic contrast-enhanced images were acquired pre-contrast and at 1, 2, and 6 minutes following intravenous contrast administration (0.1 mmol/kg).

Fig. 3.

MRI revealed a well-circumscribed mass just beneath the left nipple (white arrow). On STIR imaging (A, B), the lesion showed intermediate signal intensity with a peripheral low-signal rim. On T1-weighted imaging (C, D), the signal intensity was similar to that of the pectoral muscle. Diffusion-weighted imaging (E, F) showed no definite signal abnormality, and no significant diffusion restriction was observed on the corresponding ADC map (G, H).

Fig. 4.

On dynamic contrast-enhanced MRI, images (A) and (B) show pre-contrast T1-weighted imaging, (C) and (D) were obtained at 1 minute after contrast administration, (E) and (F) at 2 minutes, and (G) and (H) at 6 minutes. The mass beneath the left nipple demonstrated persistent enhancement (B, D, F, H; white arrow).

Fig. 5.

On contrast-enhanced MRI, internal enhancement was heterogeneous without rim enhancement (A). The time-intensity curve derived from dynamic contrast-enhanced MRI showed a slow-persistent pattern (B).

A pathological diagnosis was established by core needle biopsy. Hematoxylin and eosin staining demonstrated interlacing bundles of mature smooth muscle within the dermis without cytologic atypia or other features of malignancy, consistent with leiomyoma (Fig. 6). Immunohistochemical staining (including SMA, desmin, and ER/PR) was not performed.

Fig. 6.

Histopathological examination revealed interlacing bundles of mature smooth muscle cells within the dermis, consistent with leiomyoma. No necrosis or nuclear atypia suggestive of malignancy was observed (hematoxylin-eosin staining, x400).

At the patient's request, complete excision was not performed and the lesion is currently being managed conservatively with observation.

Discussion

Nipple leiomyomas are extremely rare benign tumors and are one of the least common subtypes of cutaneous leiomyomas [1,2]. Although leiomyomas typically arise from the arrector pili, vascular smooth, or genital smooth muscles, those originating from the nipple are rare [1]. Nipple leiomyomas typically present as unilateral, slowly enlarging nipple masses, and are generally small (with a mean diameter of approximately 2 cm) [1,2]. In the present case, no significant changes in size were observed over a 10-year period.

These tumors are often associated with pain or pruritus triggered by external stimuli such as cold, friction, or stress. Pain is also a common feature of cutaneous leiomyomas at other sites and is thought to result from the calcium-dependent contraction of smooth muscle cells [1,2,4]. Previous studies have shown a female predominance of approximately 3:1, with the tumor most commonly occurring in middle-aged women [[1], [2], [3]]. Associations with female hormones, trauma, and oral contraceptive use have been suggested as possible contributing factors [2,5].

A PubMed search identified 23 reported cases of nipple leiomyoma in males, including the present case. Cases have been reported in association with both gynecomastia and idiopathic settings, and bilateral nipple leiomyomas have also been reported [2]. Some cases have demonstrated the expression of estrogen and progesterone receptors on histopathologic evaluation [2,5]; however, no correlation with the underlying gynecomastia has been observed [6]. Because immunohistochemical evaluation of hormone receptors has not been performed in all previously reported cases, including the present one, the significance of hormone receptor expression in tumor proliferation remains unclear.

Reports describing the MRI findings of nipple leiomyomas are extremely limited, with only 1 female patient identified in our literature search [3]. Similar to ours, the lesion was well-defined with intermediate signal intensity on both T1WI and T2-weighted images (T2WI) and demonstrated a slow and persistent enhancement pattern on dynamic contrast-enhanced imaging that may be characteristic of nipple leiomyoma. In contrast to the previous report, our case differed in that the lesion was not clearly visualized on DWI, and rim enhancement was not observed on post-contrast images.

Among genital leiomyomas, including nipple leiomyomas, vaginal leiomyomas have been more frequently evaluated using MRI. These typically present as well-circumscribed lesions with low signal intensity on both T1WI and T2WI, and show strong early enhancement with persistent contrast enhancement [7]. However, it has been reported that the signal intensity on T2WI and enhancement patterns may vary depending on the proportion of capillaries and cellular components within the lesion [7]. This variability may account for the differences observed in our case. Although the lesion in our case demonstrated a slow and persistent enhancement pattern similar to a previously reported case of nipple leiomyoma, it differed in that rim enhancement was absent and the lesion was poorly visualized on DWI. In addition, the small size of the lesion may have contributed to these findings. Further studies are needed to investigate potential sex-related differences and to evaluate the relationship between imaging findings and hormone receptor expression.

Differential diagnoses of nipple leiomyoma include adenoma, intraductal papilloma, syringomatous tumor, and Paget’s disease of the breast. Nipple adenoma is a relatively rare, benign glandular tumor that arises within the ducts of the nipple or just beneath the areola. It is often associated with nipple induration, bleeding, and erosion. On MRI, it typically appears as a well-circumscribed solid mass with smooth margins and shows heterogeneous enhancement with a fast-persistent or washout pattern on dynamic contrast-enhanced imaging [8]. Intraductal papilloma is a papillary tumor arising within the ducts and contains vascular and fibrous stromal components arranged in a branching pattern. In the absence of an associated cystic component, it may appear as a well-defined mass with intermediate signal intensity on T2WI. Contrast-enhanced MRI often reveals rim enhancement, and dynamic imaging typically shows a fast washout or plateau pattern [8]. Syringomatous tumors are rare benign neoplasms arising from eccrine sweat glands, which are skin adnexal structures. Ultrasonography reveals an irregular mass in the subareolar region of the nipple, and MRI findings are generally nonspecific, except for the presence of contrast enhancement within the lesion [9]. Paget’s disease of the breast typically presents with clinical symptoms such as nipple erythema, erosion, or bleeding. MRI may show linear or segmental enhancement in cases with associated ductal extension [8]. A summary of the distinguishing MRI features is provided in Table 1. Because there is considerable overlap in imaging features among these entities, a definitive diagnosis based solely on imaging findings is often difficult. Therefore, a histopathologic examination is essential for making a final diagnosis. In addition, leiomyosarcomas can be excluded histologically by the absence of nuclear atypia and necrosis.

Table 1.

Summary of distinguishing MRI features of nipple leiomyoma and its main differential diagnoses.

Diagnosis	Margins	Diffusion restriction	Dynamic contrast enhancement	Key distinguishing feature
Nipple leiomyoma	Well-circumscribed	Variable	Slow, persistent	Rare benign smooth muscle tumor
Nipple adenoma	Well-circumscribed	Variable	Fast-persistent or washout pattern	Frequently associated with nipple erosion or bleeding
Intraductal papilloma	Well-defined	May be present	Rim enhancement; washout or plateau pattern	Ductal origin, may be associated with ductal dilatation
Syringomatous tumor	Ill-defined or infiltrative	Variable	Nonspecific enhancement	Infiltrative growth in subareolar region
Paget’s disease	Often non–mass-like	Not applicable	Linear or segmental enhancement	Associated nipple skin changes

Treatment of nipple leiomyoma is primarily symptomatic, and calcium channel blockers and alpha-adrenergic receptor antagonists are used to manage pain [10]. The definitive treatment is surgical excision of the lesion. Although recurrence data are limited, Hammer et al. [11] reported 6 cases with no recurrence over a follow-up period of up to 12 years. To date, malignant transformation has not been reported in the literature.

To our knowledge, this is the first report describing the MRI findings of nipple leiomyoma in a male patient. Previous MRI documentation has been limited to a single case report in a female patient. Although both cases shared imaging features, including a well-circumscribed mass with intermediate signal intensity on T1- and T2-weighted images and a slow, persistent enhancement pattern, our case differed in the absence of a clearly identifiable abnormality on diffusion-weighted imaging and the lack of rim enhancement. By presenting detailed multiparametric MRI findings in a male patient, this report further expands the limited imaging features on this rare entity.

Patient consent

Written and informed consent was received from the patient.