Incisional Wedge Biopsy of Subcutaneous Tumors

Subcutaneous tissue tumors are common.^2,3 Fine-needle aspiration can accurately differentiate neoplastic from inflammatory processes and is often the first test performed⁴; however, not all cytologic samples are diagnostic or accurate, especially when peripheral inflammation or necrotic centers of tumors are sampled.^4,5 Surgical biopsy is therefore often pursued as it can provide tissue that reveals the underlying architecture and interplay of cells.¹ Tumor grade can only be identified via biopsy.^1,2,6,7

Surgical biopsies are excisional or incisional. Excisional biopsy involves removal of an entire mass without prior knowledge of tumor type⁷; surgical margins may be inadequate, risking tumor regrowth, and additional aggressive surgery or adjuvant treatment (eg, radiation, chemotherapy) may be needed.⁷ Incisional biopsy involves excision and submission of a small piece of the tumor; this indicates the tumor type before definitive removal, and appropriate surgical margins can be planned.⁷

Incisional biopsies can be performed using a punch biopsy instrument, specialized biopsy needle device, or wedge technique.^1,2,7 Punch biopsies of the outer layers of a subcutaneous tumor are less likely to be diagnostic because the depth of the circular blade determines the depth of the sample.⁷ Although needle biopsies have a high rate of diagnostic accuracy, specialized cutting needles are required and advanced imaging modalities may be needed to increase the accuracy of sample retrieval.^1,2,6,7 Wedge biopsy can provide direct visualization of abnormal tissue, control of the length and depth of the sample, and avoidance of specialized equipment use.^1,7

Anesthesia is not always needed for wedge biopsies; heavy sedation, analgesics, and a local anesthetic are often sufficient.

Sample location is an important consideration for wedge biopsy of a subcutaneous tumor. Sampling from the junction of a lesion and normal tissue is commonly recommended for dermatologic biopsies^3,7; however, sampling a subcutaneous mass at this junction can lead to inadvertent spread of cancer cells beyond the original tumor.^1,7 Removal of the original biopsy site should be considered if definitive tumor excision is performed later, as the biopsy site is considered contaminated with tumor cells. Sampling closer to the center of the mass may be preferable, but areas of inflammation or necrotic debris should be avoided (Figure 1). 

Understanding the appearance of healthy tissue and normal tissue layering is key to distinguishing neoplastic from normal tissue. Familiarity with regional anatomy overlying and adjacent to a subcutaneous mass can help avoid inadvertent damage to vital structures (eg, blood vessels, nerves; Figure 2). Many tumors have a capsule or pseudocapsule, which should be grossly differentiated from normal tissue layers and penetrated during dissection to obtain a sample of the underlying tumor.^2,7

Narrow and deep wedge biopsies are most likely to obtain an accurate sample.⁷ Because the wedge biopsy site is considered contaminated, and a lengthy incision that may contain cancer cells can make definitive removal with adequate margins challenging, the skin incision should not span the entire width of the tumor. Depending on the size of the mass, the incision can vary from a few millimeters to a few centimeters.

The pathology form should be filled out completely when a biopsy sample is submitted so the pathologist can provide an informed, accurate, and clinically relevant diagnosis (see Pathology Form).⁸ A study found >88% of biopsy submission forms supplied inadequate clinical information in at least one key content area, and 3% of forms were devoid of information beyond signalment.⁹ Inadequate information significantly influenced reporting of clinical information by the pathologist.⁹

• Clippers
• Sterile surgical scrub and alcohol
• Sterile gown and gloves
• Sterile instrument pack
  • Scalpel blade handle
  • Brown-Adson thumb forceps
  • Needle holders
  • Suture scissors
• #10 or #15 scalpel blade
• Small biopsy jar with 10% buffered formalin
• 3-0 synthetic absorbable monofilament suture (eg, poliglecaprone, polydioxanone)
• 3-0 synthetic nonabsorbable monofilament suture (eg, nylon)
• Histopathology form

Clip and aseptically prepare the mass and surrounding skin.

Apply sterile drapes around the tumor or biopsy site.

Incise through the skin (A) and underlying subcutaneous tissue (B) over the mass.

Identify and incise the tumor capsule (A, arrow; subcutaneous lipoma) or pseudocapsule (B, dashed arrow; subcutaneous sarcoma).^2,7

Incise the tumor, slicing down and inward as if following the side of an inverted triangle (A). Remove the scalpel blade and angle it in the opposite direction, slicing down and inward on the other side of the imaginary inverted triangle (B).

Continue incising into the tumor until the point of the inverted triangle is reached and the wedge is released. Place the specimen in 10% neutral buffered formalin immediately after excision to limit tissue artifacts.⁸

Close the subcutaneous and subcuticular layers and the skin layers routinely.