Anatomical Basis of a Posterior Intralamellar Plane in Breast Tissue-Preservation Surgery.

Breast tissue-preservation surgery relies on the identification of anatomical dissection planes that allow surgical access while minimizing disruption of glandular and fascial structures. Although a plane between the mammary gland and the pectoralis major fascia is increasingly utilized in aesthetic procedures, its anatomical basis remains incompletely defined. The aim of this study was to describe the anatomical and histological foundations of a posterior intralamellar dissection plane located between the corpus mammae and the pectoralis major fascia and to characterize its relevance for breast tissue-preservation surgery. Eight bilateral dissections (n = 16 breasts) were performed on fresh cadavers at 2 academic anatomy centers between 2024 and 2025. Conventional breast augmentation approaches (subglandular, subfascial, and dual-plane) and breast tissue-preserving techniques were sequentially performed. Specimens underwent layer-by-layer anatomical dissection or sagittal sectioning. Macroscopic, endoscopic, and histological analyses were conducted at standardized anatomical locations using hematoxylin and eosin, Masson's trichrome, and Sirius Red/Fast Green staining. A consistent posterior lamella composed of laminated adipose and fascial layers was identified in all specimens, regardless of the surgical approach. This posterior intralamellar plane separated the corpus mammae from the pectoralis major fascia and demonstrated variable thickness but reproducible continuity. Atraumatic tunneling and balloon-assisted expansion preferentially propagated within this plane, creating a reproducible dissection space while preserving glandular, fascial, and adjacent neurovascular structures. Histological analysis confirmed a distinct laminated fascial architecture, clearly differentiated from both glandular parenchyma and underlying muscular fascia. The posterior intralamellar plane represents a consistent anatomical and histological dissection plane suitable for breast tissue-preservation surgery. Recognition of this plane provides an anatomical rationale for conservative surgical strategies that preserve glandular integrity and may facilitate posterior access aligned with native breast tissue architecture. Level of Evidence: 4 (Therapeutic)  For image description, please refer to the figure legend and surrounding text.