Encapsulated neoplasms of the thyroid gland - PubMed (original) (raw)

Review

Encapsulated neoplasms of the thyroid gland

Nikolina Dioufa et al. Virchows Arch. 2026 Jan.

Abstract

Encapsulated thyroid gland lesions, defined by complete or partial confinement within a fibrous capsule, are common findings in endocrine pathology but frequently pose diagnostic challenges. The primary difficulty lies in distinguishing benign, low-risk, and malignant neoplasms, particularly within the spectrum of follicular-patterned tumors. Accurate classification can be hindered by pitfalls such as differentiating true tumor capsule from peritumoral fibrosis, identifying capsular or vascular invasion versus reactive changes from preoperative fine-needle aspiration, and accounting for histologic and cytologic heterogeneity. In this review, we discuss the definition of true capsule and vascular invasion and how to contrast from mimics. We describe the wide spectrum of both follicular and non-follicular lesions encountered in the thyroid, and we propose a systematic diagnostic approach to encapsulated thyroid neoplasms, integrating ultrasonographic, cytologic, histologic, immunohistochemical, and molecular data, in an effort to optimize diagnostic accuracy and guide appropriate clinical management.

Keywords: Adenoma; Carcinoma; Encapsulated; Low-risk neoplasms; Neoplasms; Thyroid gland.

© 2025. The Author(s).

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Conflict of interest statement

Declarations. Ethical approval: The manuscript was prepared in compliance with the Ethical Standards of the journal. Competing interest: The authors declare no competing interests.

Figures

Fig. 1

Fig. 1

Classic examples of capsular invasion. Trans-capsular invasion/“mushrooming” of the tumor (A, B). Separate tumor foci seen within and beyond the tumor capsule (C, D)

Fig. 2

Fig. 2

A–F Example cases of mimickers of capsular invasion in daily practice due to reactive and reparative change following preoperative fine-needle aspiration, with granulation tissue formation, vascular proliferation, and fibrosis often mimicking capsular invasion, creating diagnostic pitfalls

Fig. 3

Fig. 3

Angioinvasion. The tumor adheres to the vessel wall, partially occluding the lumen (A). A layer of endothelial cells enveloping the tumor thrombus, highlighted by CD31 (B). CD61 highlights the fibrin that is intimately admixed with the tumor cells (C)

Fig. 4

Fig. 4

Stepwise microscopic assessment of thyroid lesions under low magnification, highlighting essential features for diagnostic interpretation (image created using Biorender.com)

Fig. 5

Fig. 5

Stepwise diagnostic approach depicting the microscopic criteria for assessing capsule integrity and growth behavior in encapsulated thyroid neoplasms (image created using Biorender.com)

Fig. 6

Fig. 6

Follicular adenoma, encapsulated follicular patterned, lacking invasive features and the nuclear features of PTC (A). Follicular adenoma with papillary architecture, an encapsulated neoplasm showing complex papillary infoldings of the lining epithelium, with broad papillae containing embedded follicles (B)

Fig. 7

Fig. 7

Non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP). Well-demarcated lesion with follicular architecture and nuclear features of PTC (zoomed in insert)

Fig. 8

Fig. 8

Encapsulated papillary thyroid carcinoma, classic subtype, showing well-developed tumor capsule and papillary architecture (A) with diagnostic typical nuclei of papillary thyroid carcinoma (B)

Fig. 9

Fig. 9

Minimally invasive encapsulated follicular variant of papillary thyroid carcinoma. Tumor shows capsular invasion (A) and the diagnostic nuclear features (B)

Fig. 10

Fig. 10

Poorly differentiated thyroid carcinoma. The tumor is encapsulated, showing capsular invasion (A) and insular growth pattern and lacks nuclear features of papillary thyroid carcinoma (B)

Fig. 11

Fig. 11

Concise diagnostic algorithm of encapsulated thyroid lesions (image created using Biorender.com)

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