Mucocele-like Lesions: Radiologic-Pathologic Correlation

Mucocele-like lesions (MLLs) of the breast are rare lesions described as dilated, mucin-filled cysts associated with rupture and extracellular mucin in the surrounding stroma. These lesions are of clinical concern because they can coexist with a spectrum of atypical and malignant findings, including atypical ductal hyperplasia, ductal carcinoma in situ, and invasive carcinoma including mucinous carcinoma. Imaging findings of MLLs are nonspecific and varied, although the most common initial finding is that of incidental coarse heterogeneous calcifications on mammography. Occasionally, an asymmetry or mass may be found with or without calcifications, and such MLLs have a higher rate of upgrade to malignancy at excision. Pathology findings are often descriptive given the small sample received from percutaneous biopsy, and the primary consideration is to report any associated atypia, including atypical ductal hyperplasia. There is consensus in the literature that MLLs with atypia on biopsy should undergo excision because of the average reported 17.5% (20/114) upgrade rate to malignancy. The upgrade rate for MLLs without atypia averages 4.1% (14/341). Therefore, imaging surveillance may be a reasonable alternative to excision for MLLs with no atypia on a case-by-case basis. We review MLL imaging findings, pathology findings, and clinical management and present 3 cases from our institution to add to the literature on these rare lesions.

Spectrum of Mucin-containing Lesions of the Breast: Multimodality Imaging Review with Pathologic Correlation

Mucin-containing lesions of the breast encompass a wide range of benign and malignant processes. The spectrum of histologic findings includes incidental mucus-filled benign cysts or ducts, mucocele-like lesions (MLLs), mucin-producing ductal carcinoma in situ, and invasive mucinous carcinoma. MLL is characterized by the presence of mucin-containing cysts that are typically associated with extravasated stromal mucin. MLL is often benign but can be associated with epithelial atypia or malignancy. Mucinous carcinoma represents the malignant end of the spectrum of mucinous lesions of the breast. Evidence-based literature supports a conservative approach for benign MLLs without associated atypia or malignancy, reserving excision for those lesions exhibiting such pathologic features. The most common imaging finding for MLL is microcalcifications at mammography. No specific imaging feature is predictive of malignant outcome at surgical excision. Invasive mucinous carcinoma is a heterogeneous breast tumor subtype, as defined according to the World Health Organization criteria. Mucinous carcinomas are categorized into pure (>90% mucinous component) or mixed (10%-90% mucinous component) subtypes. Pure mucinous carcinomas are generally associated with excellent prognosis and survival, with a few exceptions. Mixed mucinous carcinomas do not have the same favorable prognosis and instead behave similarly to invasive breast carcinomas of no special type. Characteristic diagnostic imaging features can be identified for mucinous carcinoma based on its mucinous and nonmucinous contents. ©RSNA, 2023 Online supplemental material is available for this article. Quiz questions for this article are available through the Online Learning Center.

Mucocele-Like Lesion of the Breast

Mucocele-like lesions (MLLs) of the breast are rare neoplasms characterized by dilated, mucin-filled epithelial ducts or cysts that can rupture and expel their contents into the surrounding stroma. They are frequently associated with atypia, dysplastic change, and, more recently, pre-malignant and malignant conditions like atypical ductal hyperplasia, ductal carcinoma, invasive carcinoma, or mucinous carcinoma. The malignant potential of MLLs is often challenging to determine from the initial histologic evaluation of a core-needle biopsy due to copious mucin and low cellularity. Therefore, at initial presentation, MLLs should be surgically excised and thoroughly evaluated for malignancy. In this paper, we present a rare case of an MLL and explore the radiology, histology, carcinogenic potential, diagnostic evaluation, and suggested management of the condition.

The Spectrum of Mucinous Lesions of the Breast

CONTEXT.—

Mucinous lesions of the breast encompass many entities ranging from benign to malignant and nonneoplastic to neoplastic. Lesions discussed under this category are mucocele-like lesion, mucinous carcinoma, mucinous micropapillary carcinoma, solid papillary carcinoma, mucinous cystadenocarcinoma, mucoepidermoid carcinoma, invasive lobular carcinoma with extracellular mucin, mucinous ductal carcinoma in situ, and metastasis.

OBJECTIVE.—

To review clinical, pathologic, and molecular features of mucinous lesions of the breast, their differential diagnoses, and challenging features on core needle biopsies.

DATA SOURCES.—

The existing scientific and clinical literature as of December 2021.

CONCLUSIONS.—

The category of mucinous lesions of the breast is vast and the differential diagnosis can be challenging, especially on core needle biopsies. In all cases, clinical, radiologic, and pathologic correlation is necessary to reach a comprehensive diagnosis. Given that the prognosis and management of each entity is different, being aware of these entities and their nuances is critical for a pathologist to guide accurate management.

Mucocele-like Lesions of the Breast

Mucocele-like lesions of the breast (MLL) are believed to be due to mucinous ducts extruding their contents into the surrounding stroma. MLLs are a rare entity usually identified by calcifications noted on routine screening mammography. Surgical excision has been recommended due to the propensity for these lesions to harbor atypical ductal hyperplasia (ADH) or malignancy. A 44-year-old female patient presented to the breast center after undergoing routine mammography which showed a group of coarse appearing microcalcifications in the outer third of the breast. After further workup, a core needle biopsy was obtained with pathology showing benign breast tissue with acellular stromal mucin pools containing dystrophic calcifications. The patient underwent surgical excision with final pathology revealing ductal carcinoma in-situ and ADH with prominent mucin production throughout the stroma.

Mucin Neovascularization as a Diagnostic Aid to Distinguish Mucinous Carcinomas From Mucocele-like Lesions in Breast Core Needle Biopsies

The distinction between mucinous carcinomas (MCs) and mucocele-like lesions (MLLs), particularly those containing detached epithelial fragments, can be problematic in the limited samples afforded by breast core needle biopsies (CNBs). Neovascularization of mucin has been proposed as a criterion to distinguish MC from MLL, but its value in helping to categorize mucin-producing breast lesions in CNB has not been previously investigated. To address this, we evaluated mucin neovascularization on hematoxylin and eosin (H&E)-stained sections of 140 CNB containing mucin-producing breast lesions including 52 MC, 17 mucin-producing ductal carcinoma in situ (mDCIS), and 71 MLL. In 116 cases with sufficient remaining material (42 MC, 16 mDCIS, and 58 MLL), we also assessed mucin neovascularization on CD31 immunostains. On H&E-stained sections, neovascularization of mucin, defined as delicate, thin-walled microvessels in mucin, and unassociated with fibrous septae, was identified significantly more frequently in MC than in MLL (69.2% vs. 14.1%; P=0.0001). The difference in the frequency of mucin neovascularization between MC and MLL was even greater on CD31 immunostains (97.6% vs. 13.8%, P<0.00001). The sensitivity, specificity, positive predictive value, and negative predictive value of mucin neovascularization for categorizing a lesion as MC were 69.2%, 85.8%, 78.3%, and 79.2%, respectively, for H&E-stained sections and 97.6%, 86.2%, 83.7%, and 98.0%, respectively, for CD31 immunostains. We conclude that mucin neovascularization is significantly more common in MC than in MLL in breast CNB on H&E-stained sections and particularly on CD31 immunostains and may be a valuable adjunct in distinguishing between MC and MLL in problematic cases.

Mucocele-like Lesion of the Breast Diagnosed on Core Biopsy: Histologic and Clinical Analysis of 78 Cases With Focus on Features Associated With Upgrade

CONTEXT.—

Mucocele-like lesion of the breast (MLL) is an uncommon entity, and recent studies show low rates of upgrade from core needle biopsy (CNB) to excision.

OBJECTIVE.—

To evaluate features associated with upgrade of MLLs diagnosed on CNB.

DESIGN.—

Seventy-eight MLLs diagnosed on CNB from 1998-2019 and subsequent excisions were reviewed. Histologic parameters evaluated included the presence of atypia, presence and morphology of calcifications, and morphologic variant (classic [C-MLL], duct ectasia-like [DEL-MLL], or cystic mastopathy-like [CML-MLL]).

RESULTS.—

Overall, 45 MLLs lacked atypia and 33 were associated with atypia (atypical ductal hyperplasia, 32; atypical lobular hyperplasia, 1). Most were C-MLLs (61) with fewer DEL-MLLs (14) and CML-MLLs (3). Half showed both coarse and fine calcifications, with fewer showing only coarse or fine calcifications, and some showing none. Subsequent excision or clinical follow-up was available for 25 MLLs without atypia-of which 2 (8.0%) were upgraded to ductal carcinoma in situ (DCIS)-and 23 with atypia, of which 4 (17.4%) were upgraded to DCIS. No cases were upgraded to invasive carcinoma. All upgraded cases showed coarse calcifications on CNB, and all upgraded cases were associated with residual calcifications on post-CNB imaging.

CONCLUSIONS.—

Most MLLs present as calcifications and nearly half are associated with atypia. Upgrade to DCIS is twice as frequent in MLLs with atypia versus those without. A predominance of coarse calcifications and the presence of residual targeted calcifications following core biopsy may be associated with higher upgrade rates.

Unusual Changing Calcification Patterns on the Mammogram in a Pure Mucocele-Like Lesion of the Breast: A Case Report

Patient: Female, 39

Final Diagnosis: Mucocele-like lesion

Symptoms: None

Medication: —

Clinical Procedure: —

Specialty: Radiology

Clinical Management of Mucocele-Like Lesions of the Breast with Limited or no Epithelial Atypia on Core Biopsy: Experience from Two Institutions

PURPOSE

Mucocele-like lesions of the breast identified on core biopsy are rare high-risk lesions associated with variable upgrade rates to carcinoma on excision. We aimed to identify the clinicoradiopathological features that can help optimize management of this lesion.

METHODS

We evaluated 50 mucocele-like lesions identified on core biopsies from two institutions, including 36 with no atypia and 14 with limited atypia. Outcome data from excision or clinicoradiological follow-up were reviewed with core biopsy results.

RESULTS

Radiological targets were calcifications in 74% of cases, calcifications with associated mass or density in 16%, and mass in 10%. One of the 16 excised lesions without atypia on core biopsy, which was a mass lesion, was upgraded to mucinous carcinoma on excision. Of the 12 excised lesions with limited atypia, none were upgraded on excision. Among the lesions not excised, 20 without atypia had a median follow-up of 61 months, and 2 with limited atypia had follow-up of 97 and 109 months. None of these 22 patients had new development of their lesions on follow-up. The upgrade rate was 2% in our entire cohort, 3% for lesions without atypia, and 0% for lesions with limited atypia.

CONCLUSIONS

Clinicoradiological surveillance can be appropriate when a mucocele-like lesion without atypia is identified on core biopsy for a non-mass lesion with pathological-radiological concordance. For mucocele-like lesions with limited atypia, a nonsurgical approach could be considered if the atypia by itself does not warrant excision. The latter recommendation requires careful clinicopathological correlation and support from additional studies.

Excision or Observation: The Dilemma of Managing High-Risk Breast Lesions

There is an enduring dilemma on the appropriate management of high-risk breast lesions; is surgical excision always warranted or can conservative management be utilized? We present cases of high-risk breast lesions diagnosed at core needle biopsy at our institution along with relevant factors to consider for appropriate management. We conclude that a nuanced approach is warranted over the broad stroke approach of surgical excision of all high-risk breast lesions.

Histological changes secondary to wire coil placement in breast tissue and lymph nodes

We describe the histological and immunohistochemical features of the changes produced by spiral coil localization wires in the breast parenchyma and lymph nodes of a total of 100 patients undergoing surgery for different breast lesions. Coil wires produced cystic lesions containing a hyaline, mucous-like, PAS-negative fluid. Cavities were lined by cells of variable morphology ranging from synovial-like cells (with a conspicuous epithelial appearance) to mononuclear or multinucleate histiocytic cells that expressed CD68, but were negative for keratins. CD3-positive/CD8-positive T lymphocytes predominated in the inflammatory reaction. Pathologists should be aware of these changes in order to differentiate coil-related lesions from other granulomatous or epithelial lesions, including mucocele-like and ductal carcinoma in situ lesions.

Mucocelelike Lesions in the Breast: Radiologic and Clinicopathologic Correlations With Upgrade Rate

OBJECTIVE

The purpose of this article is to investigate the radiologic and clinicopathologic findings of mucocelelike lesions (MLLs) and the rate of pathologic upgrade with factors predicting it.

MATERIALS AND METHODS

We reviewed our institution's database from January 2006 to December 2012 and enrolled 89 women with 89 MLLs. The pathologic findings from the initial biopsies identified 71 lesions without and 18 lesions with associated high-risk lesions. Images were reviewed according to the BI-RADS lexicon. Clinical and pathologic results were analyzed statistically, and upgrade rates were calculated.

RESULTS

Of the 89 lesions, 67 (75.3%) underwent surgical excision and 22 (24.7%) did not. After surgical excision (n = 67), one lesion was upgraded to mucinous carcinoma, three were upgraded to ductal carcinoma in situ, and 16 were upgraded to MLLs with associated high-risk lesions (29.9% total upgrade rate; 20/67). A statistically significant higher percentage of MLLs with associated high-risk lesions was observed in the surgical excision group (94.4% vs 70.4%; p = 0.036). The final pathologic diagnosis revealed larger lesions (16.4 ± 9.1 vs 12.6 ± 6.8 mm; p = 0.024) and younger patients in the high-risk group (46.9 ± 7.7 vs 50.6 ± 9.1 years; p = 0.049). Although no significant differences were observed in the imaging findings, including the BI-RADS category, upgraded lesions were seen as a mass with calcification as a predominant feature.

CONCLUSION

This study revealed no significant differences in imaging findings or BI-RADS category between high-risk and non-high-risk breast MLLs. However, we confirmed that high-risk lesions typically are seen as larger masses with calcifications.

An Update of Mucinous Lesions of the Breast

Mucinous lesions of the breast include a variety of benign and malignant epithelial processes that display intracytoplasmic or extracellular mucin, including mucocelelike lesions, mucinous carcinoma, solid papillary carcinoma, and other rare subtypes of mucin-producing carcinoma. The most important diagnostic challenge is the finding of free-floating or stromal mucin accumulations for which the significance depends on the clinical, radiologic, and pathologic context. This article emphasizes the differential diagnosis between mucocelelike lesions and mucinous carcinoma, with a brief consideration of potential mimics, such as biphasic and mesenchymal lesions with myxoid stroma ("stromal mucin") and foreign material.

Mucocele like Tumour of the Breast Associated with Ductal Carcinoma in situ and Focal Ductal Carcinoma: What is the Best Approach to these Patients?

Mucocele Like Tumours (MLT) of the breast are quite rare neoplasms displaying a broad spectrum. These lesions were considered benign initially. But now, they are believed to be related to atypical ductal hyperplasia, ductal carcinoma, or mucinous carcinoma. Preoperative diagnosis in fine needle aspiration and core biopsy is difficult. We are reporting a case of mucocele like tumour with ductal carcinoma in situ and ductal carcinoma in a 71-year-old Turkish woman. The patient had a palpable mass in her left breast. Mammograpy showed ill defined and lobulated mass with widespread tiny microcalcifications. A few cells with sporadic nuclear atypia, were detected on FNAB (Fine Needle Aspiration Biopsy). Mastectomy was done on the left side because of the suspicion of malignancy as evident by mammograpy and FNAB. We examined adequate tissue samples from resection material. Histopathologic findings were consistent with MLT and microscopic focus of ductal carcinoma was also noted in mastectomy specimen. She is currently disease-free in the 118^th month. We believe that our case will be the first patient from Turkey and will be added to the database as one of the longest term follow-up MLT cases reported. If a mucocele-like tumour is suspected in fine needle biopsy, surgical excision should be recommended and the specimen should be carefully evaluated to exclude the presence of ductal carcinoma in situ or carcinoma.

Mucocele-Like Lesions of the Breast: Rate of Upstaging and Cancer Development

BACKGROUND

Breast mucocele-like lesions (MLLs) are rare breast lesions. There is a paucity of literature on the rate of pathologic upstaging of MLL to in situ or invasive breast cancer. We sought to review our experience with MLL at a tertiary care center and review published literature.

METHODS

A retrospective review was undertaken of all patients with breast MLL at the Mayo Clinic, Rochester, from 1998 to 2016. Descriptive statistics were performed.

RESULTS

Overall, 30 patients were diagnosed with MLL, with a mean age of 54.6 years (range 51-58). Calcifications on screening mammogram were the most common method of MLL detection (n = 26, 86.7 %), with core needle biopsy (CNB) being performed in 29/30 patients. MLL with atypia was identified in 14 patients (48 %), and surgical excision was performed in 26 patients. Disease was upstaged to invasive disease in one patient (3.8 %) who presented with a palpable mass. With a median duration of follow up of 3.5 years [interquartile range 1-7.1], two patients developed contralateral invasive breast cancer (both patients had a remote history of invasive breast cancer on that side), and one patient developed contralateral in situ disease. Review of the literature demonstrates a 2.9 % upgrade rate of MLL without atypia on excisional biopsy.

CONCLUSIONS

The upstage rate of MLL identified on CNB to invasive disease at surgical excision in this series was 3.8 %. In cases with MLL presenting as calcifications, no cases were upstaged in this series. Across the literature, upstage rates of MLL without atypia on CNB are low, indicating excisional biopsy may be avoided in these cases.

[Benign proliferative breast disease with and without atypia]

In the last few years, diagnostics of high-risk breast lesions (atypical ductal hyperplasia [ADH], flat epithelial atypia [FEA], lobular neoplasia: atypical lobular hyperplasia [ALH], lobular carcinoma in situ [LCIS], radial scar [RS], usual ductal hyperplasia [UDH], adenosis, sclerosing adenosis [SA], papillary breast lesions, mucocele-like lesion [MLL]) have increased with the growing number of breast percutaneous biopsies. The management of these lesions is highly conditioned by the enlarged risk of breast cancer combined with either an increased probability of finding cancer after surgery, either a possible malignant transformation (in situ or invasive cancer), or an increased probability of developing cancer on the long range. An overview of the literature reports grade C recommendations concerning the management and follow-up of these lesions: in case of ADH, FEA, ALH, LCIS, RS, MLL with atypia, diagnosed on percutaneous biopsies: surgical excision is recommended; in case of a diagnostic based on vacuum-assisted core biopsy with complete disappearance of radiological signal for FEA or RS without atypia: surgical abstention is a valid alternative approved by multidisciplinary meeting. In case of ALH (incidental finding) associated with benign lesion responsible of radiological signal: abstention may be proposed; in case of UDH, adenosis, MLL without atypia, diagnosed on percutaneous biopsies: the concordance of radiology and histopathology findings must be ensured. No data is available to recommend surgery; in case of non-in sano resection for ADH, FEA, ALH, LCIS (except pleomorphic type), RS, MLL: surgery does not seem to be necessary; in case of previous ADH, ALH, LCIS: a specific follow-up is recommended in accordance with HAS's recommendations. In case of FEA and RS or MLL combined with atypia, little data are yet available to differ the management from others lesions with atypia; in case of UDH, usual sclerosing adenosis, RS without atypia, fibro cystic disease: no specific follow-up is recommended in agreement with HAS's recommendations.