Cryostat Article #3: Cryostats for Mohs Surgery in Dermatology

Cryostat Article #3: Cryostats for Mohs Surgery in Dermatology

Welcome to the summer! As you are enjoying the summer sun and hot weather, we hope you are taking care of your skin when you’re outdoors by wearing sunscreen. Why? Because skin cancer is a risk with sun exposure. The incidence and diagnosis of skin or cutaneous cancer are steadily rising. The most common skin cancers are basal cell carcinoma, squamous cell carcinoma, and melanoma. Skin cancer is the most common cancer in the United States and worldwide (Figure 1). In fact, 1 in 5 Americans will develop skin cancer by the age of 70. When melanoma is detected and treated early, the 5-year survival rate is 99%.

Figure 1. Skin cancer is the most common type of cancer, and includes basal cell carcinoma, squamous cell carcinoma, and melanoma.

One common application of the clinical cryostat is in dermatology, where cryostats are used for analyzing tissue samples from Mohs surgery. This week, we will explore this area of clinical cryostats, and see how cryostats are used in private practices and clinical histology labs by dermatologists.

What is Mohs surgery?

Mohs micrographic surgery (MMS) is the gold standard of care for the treatment of high-risk nonmelanoma skin cancers, and is also increasingly used to treat melanoma. Cutaneous malignancies, or skin cancers, include squamous cell carcinoma (SCC), basal cell carcinoma (BCC), and melanoma. Typically, Mohs surgery involves surgically removing the minimal amount of tissue to eradicate cancerous tissue while preserving normal skin (Figure 2).

Figure 2. Left panel shows a suspicious mole on a patient’s forehead. Middle panel illustrates the horizontal layers of skin tumor excised during Mohs surgery. Right panel shows three small specimens mounted onto a glass slide after cryostat sectioning.

Mohs surgery was originally developed in 1941 by Dr. Frederick Mohs. Cancers like SCC and BCC grow in the skin by extending fingerlike projections into the surrounding connective tissue. These tumor strands may go undetected with standard excision techniques, which are geared more towards tumors that grow in a sphere-shaped mass. The Mohs surgery technique allows tissue to be removed in thin layers, and all margins of the specimen are mapped to determine the tumor margins (i.e., if the tumor remains). As a result, the skin tumor is precisely identified and maximum amounts of normal skin can be retained. Cure rates are very high and Mohs surgery can usually be performed on fresh tissue in 1 day on an outpatient basis.

How are cryostats used in Mohs surgery analysis?

For Mohs surgery, a thin, horizontal layer of tissue is removed over the area of concern. This layer is divided into smaller specimens for frozen sections on a cryostat. The edges of the extracted tissue layer is dyed to provide spatial orientation when the tissue is examined later on on a glass slide. The specimens are prepared in a cryostat and sectioned (Figure 3). Cut tissue sections are mounted onto glass slides, stained, and microscopically examined.

The location of tumor cells are then indicated on a map. The above steps are repeated to excise additional tissue layers in the areas with tumor, until cryostat-sectioned tissue samples show a cancer-free plane. The skin defect created by the fresh tissue Mohs surgery can heal or be closed.

Figure 3. Left panel shows skin samples mounted on a cryostat specimen holder for frozen section cutting. Right panel shows an H&E-stained pathology of excised tissue from Mohs surgery

What are key cryostat features for dermatology?

In a dermatology practice, the cryostat will likely be the largest single purchase for the clinic or laboratory. Thus, users should make sure that they purchase a cryostat with all important features for frozen section creation. The cryostat should be located in an easily accessible area. Key components of the cryostat include the microtome, cryochamber, blade holder, handwheel, and freeze plate. For Mohs surgery samples, the cryostat should be kept between -20 and -25 C. The cryostat for dermatology needs to have a robust freeze system, because multiple frozen samples are main daily, so the window to the freeze chamber will be repeatedly opened and closed. A heat extractor and Peltier cooling tray are also desirable to help speed up fresh tissue sample preparation (Figure 4).

Figure 4. Heat extractors are extremely helpful in rapidly freezing embedded skin biopsies (left). Prepared samples are then mounted and sectioned on cryostats (right).

The Precisionary Cryostat CF-6100 meets all of the above criteria. Our cryostat comes with a dual compressor system, meaning that there are two compressors for helping maintain cold temperatures in the freeze chamber. The CF-6100 cryostat has a built in Peltier plate with room for 36 specimens, so that users don’t have a backlog of tissue samples to process. Our cryostat set comes with the heat extractor, Peltier cooling, UV disinfection lamp, and LED touchscreen (all included with no additional cost).

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