Tissue-Specific Sectioning Guide: Troubleshooting

 Routine histological sectioning forms the bedrock of pathological diagnosis, and the quality of the sections is a crucial guarantee for pathologists to make accurate diagnoses. During microtomy, numerous issues can arise—such as tissue sticking to the blade, cracking, wrinkling, rolling, or fragmenting. These problems not only compromise section quality and speed but also delay turnaround times. Based on our daily practice with various tissue types, we have summarized several hands-on insights and experiences to share with fellow professionals.

1. Lymph Node Tissue

• Sampling: Lymph node tissues are characterized by a dense structure and high cellularity. When sampling, the tissue must be cut to a uniform thickness, ideally between 0.2 and 0.3 cm.

• Fixation and Processing: Lymph nodes possess a dense connective tissue capsule that hinders the penetration of fluids. Consequently, the fixation time needs to be extended by 6 to 12 hours (or overnight), allowing them to be dehydrated alongside routine tissues the following day. If using neutral buffered formalin for fixation and ethanol for dehydration, the processing time should be doubled, while the xylene clearing step can be appropriately shortened.

• Microtomy: Because a section thickness of 2–3 μm is required, the tissue becomes highly brittle. During sectioning, wrinkles are difficult to expand, and cracks or unevenness often occur. To resolve this, avoid freezing the wax blocks for too long. Once the frozen block is faced down to its maximum surface area, press your thumb (warmed with warm water) against it for 5–6 seconds, ice it immediately for 3–4 seconds, and section it right away. This technique yields intact, crack-free, and continuous serial sections.

• Water Bath: The water bath temperature should be maintained at around 35°C. If it is too high, micro-wrinkles will fail to open; if it is too low, the section will remain uneven and fail to adhere firmly, leading to section detachment.

• Staining: The hematoxylin staining time should be shorter than routine protocols, typically 3 to 5 minutes. Alternatively, a dedicated staining program can be set up specifically for solid tissues like lymph nodes.

2. Fatty Tissue

Fatty tissues are rich in lipid droplets, which are difficult to completely dissolve with standard dehydrating agents, preventing paraffin from fully infiltrating and fixing the tissue. Since fixation aims to increase tissue hardness for easier sectioning, extending both fixation and infiltration times is critical. Sampling should not be too thick.

During sectioning, after facing the block to its maximum area, place an ice cube directly onto the wax block for 5–10 seconds before sectioning immediately. The low temperature temporarily solidifies the poorly infiltrated lipid droplets, allowing for more intact sections. The section thickness can be adjusted to 5–6 μm. Floating and mounting the sections must be done quickly, and the water bath temperature should not exceed 42°C.

3. Bone Marrow and Bone Tissue

Decalcification is the key step in preparing bone marrow and bone tissue sections.

• Bone Marrow: A 7% aqueous hydrochloric acid solution is commonly used for decalcification. Because the hardness of submitted bone marrow specimens varies, timing is critical. If the time is too short, the tissue remains hard, preventing continuous sectioning; if too long, the tissue turns gray, which impairs diagnosis. Bone marrow tissue is ready when it begins to float in the decalcification solution, typically taking 2 to 5 minutes.

• Bone Tissue: Bone tissue must also be decalcified before sectioning. A 17% aqueous nitric acid solution is frequently used, with a duration of 12 to 24 hours, or until a pin can easily penetrate the tissue.

• Microtomy and Mounting: Before sectioning, the wax block must be faced slowly and thinly—especially for thin bone fragments—to prevent the bone tissue from being completely shaved away. The section drying time should be extended to prevent tissue detachment.

4. Blood Clots

Dehydrated blood clots tend to become very dry, causing them to crumble and fragment during sectioning. To improve sectioning speed and quality, press a warm, water-moistened thumb against the faced tissue surface for a few seconds, back the block up slightly, and then section rapidly. Extend the drying time to prevent section detachment during staining.

5. Skin Tissue

Skin tissue has a complex, multi-layered structure with varying degrees of density across different layers. Dehydration times can be relatively extended for these specimens. During embedding, the epidermis and subcutaneous tissue must be aligned on the exact same plane to preserve the anatomical layers in the section.

When mounting the block on the microtome, orient the epidermal layer facing upward. Section from the inner layers outward, leaving the stratum corneum for last. This approach ensures intact sections, as the stratum corneum is the densest and most brittle layer. Extend the drying time to prevent tissue detachment.

6. Brain Tissue

Brain tissue is loose, cellularly sparse, soft, and highly friable. Generally, the sampling thickness should be less than 2 mm. Poor dehydration will negatively impact paraffin infiltration, so dehydration times can be appropriately extended.

Because the tissue becomes brittle post-dehydration, handle it gently with forceps during embedding and avoid applying heavy pressure to prevent crushing. During microtomy, the tissue tends to stick to the blade, and wrinkles are difficult to flatten. Therefore, the block should be chilled in the refrigerator for a longer duration, and the sectioning method should mirror that used for lymph nodes. When floating sections, place them in cool water first to fully expand micro-wrinkles, then transfer them via a glass slide to the heated water bath for final expansion. Avoid overly long drying times.

📌 Key Takeaways for the Sectioning Process

1. Blade Management: When using a new microtome blade, try to section smaller tissues or solid tissues (like lymph nodes) first, followed by fat and muscle, and save bone tissues for last.

2. Blade Positioning: Do not face the block and cut the actual sections at the exact same position on the blade. Face the block on one side of the blade, then slide to the other side for final sectioning. This extends blade life and ensures section quality.

3. Drainage Before Drying: Before placing slides onto the section dryer/slide warmer, lean the freshly mounted slides vertically against the edge of the instrument to drain excess water. Otherwise, trapped water may disperse the tissue, destroying its structural integrity.

4. Automation Advantages: Utilize automated tissue processors and strainers to maintain constant temperatures, precise timing, and standardized protocols, thereby eliminating the inconsistencies associated with manual operations.

   
   

   **Part of our Tissue Sectioning Troubleshooting series.** See the [complete 9-step guide]or jump to another phase: [Fixation & Grossing] | [Dehydration & Embedding]| [Sectioning & Floating]