A reticulin stain is a special stain that pathologists use to see a fine network of fibers in tissue. These fibers, called reticulin fibers, form a thin supporting mesh in many organs. The stain colors the fibers black, so the pathologist can see their pattern. Changes in this mesh help pathologists diagnose conditions of the bone marrow, liver, adrenal gland, and ovary.
This article explains how the reticulin stain works and how pathologists use it on bone marrow, liver, adrenal, and ovarian samples.
What are reticulin fibers?
Reticulin fibers are very thin threads made mostly of a type of collagen. They form a delicate framework that holds cells in place. Reticulin fibers are common in the liver, bone marrow, spleen, lymph nodes, and adrenal glands.
On a routine slide stained with hematoxylin and eosin (H&E), reticulin fibers are almost invisible. The reticulin stain makes them easy to see.
How does a reticulin stain work?
The reticulin stain uses silver. The laboratory treats a thin slice of tissue with a silver solution. The silver sticks to the reticulin fibers and turns them black. The rest of the tissue stays pale.
The pathologist then looks at the pattern of black fibers under the microscope. The pathologist checks whether the fibers are present, how thick they are, and how they surround the cells.
Why do pathologists use a reticulin stain on a bone marrow biopsy?
A reticulin stain on a bone marrow biopsy shows whether the marrow has extra fibers. Doctors call extra fibers in the marrow myelofibrosis, a type of fibrosis. Myelofibrosis can crowd out the cells that make blood.
Pathologists grade marrow fibrosis on a scale from MF-0 to MF-3:
- MF-0. A few thin reticulin fibers lie scattered and do not cross each other. This is normal.
- MF-1. A loose network of fibers is present, with many crossing points.
- MF-2. The fibers are dense and widespread. Small bundles of thicker collagen may appear.
- MF-3. The fibers are dense and widespread, with coarse collagen bundles. The bone itself is often thickened.
The grade is especially important in myeloproliferative neoplasms. In primary myelofibrosis, MF-0 or MF-1 points to the early, or prefibrotic, stage. MF-2 or MF-3 points to the overt, or fibrotic, stage. Higher grades predict a worse outlook.
Why do pathologists use a reticulin stain on a liver biopsy?
In the liver, the reticulin stain outlines the plates of liver cells. Normal liver cells line up in thin plates, one or two cells thick. Reticulin fibers run along both sides of each plate.
The stain helps pathologists tell hepatocellular carcinoma apart from noncancerous growths:
- Noncancerous growths. A hepatocellular adenoma usually keeps its reticulin framework and thin plates.
- Hepatocellular carcinoma. The tumor loses some or all of its reticulin fibers. The plates of cancer cells become thick, often three or more cells across.
Where else do pathologists use a reticulin stain?
The reticulin stain also helps in several other organs:
- Adrenal gland. Normal adrenal cortex has a regular mesh of reticulin, like an intact fishing net. In adrenal cortical carcinoma, this mesh is broken. Pathologists use a disrupted reticulin pattern, plus necrosis, many dividing cells, or vessel invasion, to separate carcinoma from adrenal cortical adenoma.
- Ovary. In a thecoma or fibroma, reticulin surrounds every single cell. In an adult granulosa cell tumor, reticulin usually surrounds groups of cells instead. This difference helps distinguish the tumors.
- Soft tissue tumors. The fiber pattern around tumor cells can give clues about the tumor type.
What might my report say about a reticulin stain?
Your report may describe the reticulin stain in several ways:
- Reticulin framework intact or preserved. The normal fiber mesh is present.
- Reticulin loss or disrupted reticulin. The normal mesh is broken or missing.
- Reticulin fibrosis, grade MF-0 to MF-3. This describes the amount of extra fibers in a bone marrow biopsy.
- Thickened liver cell plates. The liver cells form plates more than two cells thick.
Questions to ask your doctor
- Why did the pathologist order a reticulin stain?
- Was the reticulin framework normal or disrupted?
- What grade of marrow fibrosis did my bone marrow biopsy show?
- How does the fibrosis grade affect my diagnosis or outlook?
- Does the reticulin pattern support a noncancerous or a cancerous diagnosis?
- Were other stains or tests done along with the reticulin stain?
- Will I need a repeat biopsy to follow the fibrosis over time?
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