Overview
Impression smear, also known as touch imprint or imprint cytology, is a rapid cytological technique in which freshly cut tissue is gently pressed onto a glass slide to transfer surface cells. It provides quick cellular details with minimal processing and is often performed intraoperatively or at the bedside. Impression smears were traditionally used as a substitute for frozen section in selected situations and are interpreted in a manner similar to FNAC smears.
Symptoms
Impression smear is not symptom-driven but is performed based on clinical suspicion of disease. It is commonly used in patients undergoing surgery for tumors, lymph node enlargement, organ transplantation, or suspected malignancy. Patients may present with lumps, masses, effusions, weight loss, fever, or organ-specific symptoms that require rapid pathological assessment during or immediately after tissue sampling.
Causes
Impression smears are used to evaluate cellular changes caused by benign or malignant conditions, infections, and inflammatory processes. They help identify tumor cells, metastatic deposits, reactive changes, and microorganisms. This technique is particularly useful for lymph nodes, breast masses, thyroid nodules, soft tissue tumors, and biopsy cores. It allows rapid assessment of tumor margins, lymph node involvement, and transplant organ viability.
Risk Factors
Situations favoring impression smear use include intraoperative decision-making, limited tissue availability, and the need for rapid diagnosis. It is especially helpful when frozen section facilities are unavailable. However, hard or calcified tissues, fatty tissues, and very small biopsies yield suboptimal smears. Sampling error, cellular overlap, and limited architectural detail are important limitations that can affect interpretation.
Prevention
While diseases diagnosed by impression smear cannot be prevented, early use of this technique helps prevent delays in diagnosis and unnecessary repeat procedures. Proper tissue handling, gentle touch technique, immediate fixation or staining, and correct slide labeling improve smear quality. Combining impression smear findings with histopathology, special stains, and immunohistochemistry ensures accurate diagnosis and optimal patient management.
