Acinar

Acinar refers to a small, cluster-like or grape-like grouping of cells or glands, often the smallest functional unit of a gland or organ. In the lungs, the acinus is the tiny structure at the end of the smallest airways where oxygen and carbon dioxide are exchanged. In pathology, "acinar" describes a tissue pattern in which cells form rounded, gland-like spaces.

Origin

From the Latin word acinus, meaning "berry" or "grape," referring to the clustered, berry-like appearance of these structures under a microscope. The term has been used in anatomy since the 18th century.

Significance in Asbestos Context

Acinar appears in pathology reports for two important reasons. First, in lung anatomy, the acinus is where asbestos-related scarring (asbestosis) often begins and where adenocarcinomas of the lung frequently arise. Second, when a pathologist describes a tumor as having an "acinar pattern," this is one of the recognized growth patterns of epithelioid mesothelioma and of lung adenocarcinoma, and distinguishing between the two is critical because mesothelioma and lung cancer follow different treatment paths and may involve different defendants in a legal claim. Special stains and immunohistochemistry are usually needed to tell them apart, and patients should make sure this work was done before accepting a diagnosis.

Example Sentence

The pathology report described an "acinar growth pattern," and the oncologist ordered additional immunohistochemical stains to confirm whether the tumor was epithelioid mesothelioma or a lung adenocarcinoma.

Related Terms

Epithelioid Mesothelioma, Adenocarcinoma, Immunohistochemistry, Histopathology, Alveolus, Tubulopapillary

Notes

• If your pathology report mentions an "acinar pattern," ask your doctor whether immunohistochemical stains (such as calretinin, WT-1, CK5/6, TTF-1, and Napsin A) were performed to distinguish mesothelioma from lung adenocarcinoma.
• Request a copy of the full pathology report and the immunohistochemistry panel results. These documents are central to both treatment planning and any legal claim.
• Consider asking for a second pathology review at a mesothelioma specialty center, since acinar mesothelioma is uncommon and can be misread as lung cancer.
• Preserve all biopsy slides and tissue blocks; they may be needed later for additional testing or expert review.