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Ultrasound-guided biopsy for soft tissue sarcoma


Medical editor Arne Heilo MD
Radiologist
Oslo University Hospital

General

Ultrasound-guided biopsy is the most precise and gentle method of obtaining a representative sample of a suspected soft tissue sarcoma. The technique has a high diagnostic precision, is sensitive, and specific with regards to malignity.

During an ultrasound guided biopsy, it is important that a cytologist is present for immediate determination of the quality of the material either as aspirate or imprint. This also provides good possibilities to ensure material for supplementary examinations. Usually, it is important to remove unfixed biopsy material for cytogenetic analysis and genetic examinations.

Before the examination, the localization of the puncture is meticulously planned to include the biopsy canal to be removed during a surgical resection of the tumor.

Indication

  • Tumor in soft tissue suspect of sarcoma

Goal

  • Obtaining representative material of the tumor to give a diagnosis cytologically or histologically.

Equipment

  • To examine and puncture the tumor, the ultrasound probe chosen should give the best detail resolution and simultaneously give satisfactory overview.
  • For cytological biopsy, a 21-27 G needle is used depending on tumor type and vascularisation.
  • For histological biopsy, a biopsy gun with a 14-18 biopsy needle is chosen.

Preparation

  • Local anesthetic is administered around and sometimes into the tumor to be sampled.
  • The patient should be positioned to provide optimal access to the tumor.

Implementation

Cytological specimen

For a cytological specimen, the sample is most often taken without aspiration. The needle's capillary action alone provides the best cytological material. The exception is lipomatous tumors in which a 21 G cannula and aspiration is necessary to obtain sufficient material.

  • The needle is inserted into the tumor and moved in and out in the same plane to liberate cell material.
  • The number of punctures for cytology depends on the type of tumor.
  • The material should be immediately transferred to a slide to avoid coagulation. The specimen should be air-dried and stained.

Histological biopsy

For a histological biopsy, the area of skin is washed and the procedure is carried out aseptically. The biopsy access is discussed with a surgeon beforehand.

  • After local anesthesia has been injected with ultrasound guidance, a small incision is made in the skin to insert the thicker needle. When the needle is in the correct position, a "shooting" mechanism is triggered and a tissue specimen is automatically sampled.
  • The biopsy material is pushed a few times onto the slide to make a cytological imprint.
  • Depending on the type of tumor, the material is put in Ringer solution or formalin for histopathological examination. 
  • The skin where the puncture is made is tatooed in order for the biopsy canal to be removed with the tumor if sarcoma is present.
  • The puncture point is covered with a bandage.

Follow-Up

  • Complications after the procedure seldom occur.
  • Mild irritation at the puncture point may occur.
  • Cytological and histological biopsies can in rare cases cause bleeding into surrounding tissue.
  • Cytology results from the specimen are available usually after 2-3 days while histology results are usually available after 1-2 weeks, depending on the type of tumor.

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