MRI-Guided Biopsy

MRI-directed biopsy is a technique for sampling a lesion that is best seen on MRI, using MRI to plan and in some methods to direct the needle.

The lesion may be invisible or poorly seen on ultrasound or CT, and the combination of the best soft tissue contrast and multiplanar imaging allows precise targeting without ionising radiation.

There are three approaches. In bore biopsy uses a wide bore scanner and MR-compatible needles, with the patient on the table and the needle passing through a grid or a sleeve, and images are taken during the procedure to confirm the needle position.

Cognitive biopsy uses the MRI to plan, and the operator targets the lesion by memory with ultrasound. Fusion biopsy overlays the MRI on live ultrasound with software, and samples the lesion in real time.

The procedure is used for the prostate (the commonest use), the breast (lesions seen only on MRI), the brain (stereotactic biopsy) and, less often, bone, liver, kidney, pelvic and musculoskeletal lesions. Prostate in bore biopsy takes 45 to 90 minutes, and MRI-directed breast biopsy takes 30 to 60 minutes.

Targeted prostate biopsy finds clinically significant cancer in 30 to 40% more men than systematic biopsy alone, and finds 10 to 20% fewer insignificant cancers. In bore breast biopsy for MRI-only lesions has a malignancy yield of about 20 to 35% and a technical success rate over 95%.

Indications.

• Prostate: MRI-visible lesion with a high likelihood of clinically significant cancer, rising prostate specific antigen after a negative systematic biopsy, active surveillance, and focal therapy planning.
• Breast: suspicious lesion seen only on MRI, with no corresponding finding on mammography or targeted ultrasound (second look ultrasound is done first).
• Brain: lesions in deep, eloquent or small sites needing a precise approach (stereotactic or interventional MRI).
• Musculoskeletal: bone and soft tissue lesions seen best on MRI, osteoid osteoma and marrow lesions.
• Other organs: liver, kidney, pelvic and retroperitoneal lesions that are poorly seen on other imaging.
• Treatment: MRI-directed ablation or focused ultrasound uses the same navigation.

Contraindications. Uncorrectable bleeding disorder, active infection at the site (acute prostatitis, mastitis), MRI-unsafe implants, and patients who cannot lie still or cooperate. Relative contraindications include anticoagulation that cannot be stopped safely, allergy to contrast or local anaesthetic (when used), claustrophobia, and large body size exceeding the bore.

Preparation.

• Informed consent, with the benefits, alternatives (ultrasound or CT-directed biopsy, surgical excision, surveillance) and risks explained.
• Review of the MRI, blood tests (full blood count, platelets, coagulation, creatinine), and medicines. Antiplatelet drugs and anticoagulants are managed by the local rule, usually stopping warfarin and direct anticoagulants for several days.
• Prostate: antibiotic prophylaxis (a fluoroquinolone is avoided in many places because of resistance, so local cover is used), a rectal enema, and urine culture.
• Breast: timing in the second week of the menstrual cycle in pre-menopausal women when possible, to reduce background enhancement.
• Intravenous access, monitoring, and, where needed, light sedation. Contrast is given for breast and some prostate lesions.

Technique. The patient lies in the position for the target (prone with the breast hanging in a dedicated coil, prone or lateral for the prostate with a transrectal or transperineal approach, or supine for the body).

Localiser images identify the lesion, and a grid or sleeve with a marker is placed.

For in bore biopsy the entry point and depth are calculated on the MRI. Local anaesthetic is infiltrated, and an MR-compatible needle (non-ferromagnetic) or introducer is advanced.

Images confirm that the needle tip lies in the lesion, and cores are taken with a vacuum assisted or spring loaded device (a vacuum assisted needle for the breast and bone, 18-gauge cores for the prostate, 3 to 5 cores for each lesion).

A marker clip is left in the breast lesion.

Fusion biopsy: the MRI with the lesion outlined is registered to live transrectal or transperineal ultrasound, and the lesion is sampled with 2 to 5 targeted cores, followed by systematic cores in many centres. Brain procedures use a frame or a frameless system with MRI or intraoperative MRI.

Findings on completion.

• Technical success: the needle in the target on post-sampling images, with adequate cores.
• Targeted cores contain tissue, and a biopsy marker is placed in the breast and in some prostate lesions.
• Post-procedure images show the needle track, small haematoma, and the clip position for follow up and surgery.
• Pathology: the histology result is matched with the imaging. Benign results that do not explain the imaging (discordant) lead to repeat sampling or excision, and concordant benign results lead to follow up.
• Breast: malignancy, high risk lesions (atypical hyperplasia, radial scar, papilloma) that need excision, and benign findings.
• Prostate: cancer with grade and extent, or no cancer in the target (which does not exclude cancer).

Critical findings needing immediate action. Uncontrolled bleeding or large haematoma, sepsis after prostate biopsy (fever with chills, retention), pneumothorax, cord or nerve injury, and discordant or high risk pathology that needs treatment planning. These need prompt clinical review and supportive treatment.

Complications. Complications are uncommon.

Haematoma and bleeding (breast haematoma in 1 to 3%, haematuria and haematospermia in prostate biopsy in over 50%, and rectal bleeding in up to 10%), infection (prostate sepsis in 1 to 3%, mastitis under 1%), urinary retention (1 to 2%), vasovagal reactions, pain, and failure to sample the lesion (1 to 5%).

Rare complications are pneumothorax in chest wall lesions, nerve injury, and tumour seeding.

Missing the target is more likely with patient movement, lesion movement and registration error. A normal result needs correlation with the MRI and repeat imaging if suspicion remains.

Aftercare.

• Observation for 30 to 60 minutes. Compression for breast biopsy and pressure on the perineum or rectum for the prostate.
• Advice about bruising, mild pain (paracetamol), and avoiding strenuous activity and aspirin or anticoagulants for 24 to 48 hours (restart as directed by the team).
• For the prostate: expect blood in urine and semen for weeks, drink fluids, and finish antibiotics as prescribed.
• Return for fever over 38 degrees, chills, urinary retention, heavy bleeding, expanding swelling, worsening pain or neurological symptoms.
• Results are discussed in a multidisciplinary meeting with the imaging, and follow up is set (repeat MRI at 6 to 12 months for benign concordant breast results).
• Marker clips direct later surgery, and are documented.

Special groups.

• Patients on anticoagulants: bridging decisions with the prescribing team.
• Patients with implants: confirm MRI conditional status, with a team of MRI safety staff.
• Women who are pregnant or breast feeding: avoid contrast when possible. Lactation does not need interruption for most agents.
• Children: sedation or anaesthesia is usually needed.
• Patients with claustrophobia or large body size: open or wide bore scanner or an alternative approach (fusion or cognitive biopsy).
• Regions: MRI-directed biopsy is available only in a few referral centres. Ultrasound directed biopsy, stereotactic mammography biopsy and surgical excision are the usual methods.