Principle of coaxial system operation
A coaxial system is used for targeted tissue acquisition. The instrument is inserted into the target lesion (for example, access to a pancreatic tumor may be achieved via the gastric antrum). A trocar is housed within the system, with a dense artifact visible at its tip on imaging.
Following precise positioning, the trocar is withdrawn while the cannula remains in the tissue (in situ). An automated cutting needle is inserted through this guiding channel. This method allows multiple biopsy samples to be obtained by changing the angles of the cutting needle without requiring repeated punctures of surrounding structures.
Post-procedural complications
Following the removal of the biopsy system, follow-up imaging may reveal a limited collection of free gas (e.g., outside the stomach in transgastric access). If the patient exhibits no clinical symptoms of complications, they can be discharged for observation shortly thereafter. In the standard situations described, safe discharge is possible as early as 6 hours post-procedure.
Role of post-biopsy staging
If histological examination confirms the presence of cancer, precise staging is critically important. It is essential for assessing the locoregional spread of the tumor and detecting distant metastases.
Diagnostic imaging plays a major role in this process. Staging results provide crucial prognostic information and, along with the histological grade, expected biological behavior of the tumor, patient age, and clinical status, determine the treatment strategy.
In the past, various organs had their own classification systems: the Robson system for kidneys, the Dukes' classification for colorectal cancer, the Royal Marsden system for testicular germ cell tumors, and the FIGO classification for gynecological oncology. However, an ideal system must be simple, precise, and universal.
TNM staging system
The current universally accepted standard is the TNM system, developed by the American Joint Committee on Cancer and the Union for International Cancer Control (originally proposed by Pierre Denoix in the 1940s).
Evaluation is carried out across three categories:
- T (Tumour) — local extent of the primary tumor. Possible variants include: Tx (cannot be assessed), T0 (no evidence of primary tumor), Tis (carcinoma in situ without evidence of invasion), and T1–T4 (increasing degree of invasion).
- N (Node) — regional lymph node involvement. Categories: Nx, N0 (no regional lymph node metastasis), and N1–N3 (increasing degree of involvement).
- M (Metastasis) — distant metastases. Designated as Mx, M0 (no metastases) and M1 (metastases present). To specify the localization, the following codes are used: PUL (lungs), OSS (bones), HEP (liver).
To provide further detail, letter subcategories 'a' or 'b' may be added to the categories, along with prefixes: c (clinical), p (pathological), and y (staging after neoadjuvant radiation therapy).
General rules for TNM application
- Clinical stage (cTNM) is established based on physical examination and imaging modalities. Following microscopic examination, it may be revised to the pathological stage (pTNM).
- Rule of doubt: in case of equivocal findings (e.g., imaging signs of pelvic wall invasion that do not allow for a definitive diagnosis without histology), the lower, less advanced category is always selected.
- The stage established prior to the start of treatment is recorded in the medical chart and remains unchanged throughout the course of therapy.
- In cases of multiple simultaneous primary tumors, staging is based on the lesion with the highest 'T' category. If the lesions are located in paired organs, a separate TNM stage is assigned to each tumor.
Because the TNM system is complex, staging groups from 0 to IV are used for convenience. They increase as the tumor process becomes more advanced.
Briefly: answers to topical questions
What three-letter codes are used to designate the localization of distant metastases (M) in the TNM system?
The localization of distant metastases is designated by standard three-letter codes.
- PUL — lung
- HEP — liver
- OSS — bones
- BRA — brain
- LYM — lymph nodes
- MAR — bone marrow
- PLE — pleura
- PER — peritoneal cavity
- SADP — adrenal glands
- SKI — skin
- OTH — other sites
What imaging methods are used for guidance during needle biopsy?
Ultrasound, CT, MRI, fluoroscopy, and PET/CT, as well as image fusion technologies, are used for needle biopsy guidance.
- Ultrasound — real-time needle visualization, absence of ionizing radiation
- CT — one of the main modalities, particularly for lung and bone lesion biopsies
- MRI — used for prostate, breast, and bone marrow lesion biopsies
- Fluoroscopy — most commonly used for musculoskeletal system biopsies
- PET/КТ — can be used to identify and biopsy lesions that are poorly visible on standard CT but detected by FDG uptake
- Fusion imaging — combining real-time ultrasound with previously acquired CT or MRI images
What are the absolute contraindications to image-guided percutaneous biopsy?
The sources list the following contraindications for image-guided spinal biopsy:
- Uncorrectable coagulopathy
- Non-compliant patient — inability to cooperate
- Hypervascular lesion in the cervical or thoracic spine
- Anatomically difficult or unsafe location for access
- Risk of spreading infection to the bone
Sources generally do not list general contraindications for percutaneous biopsy of internal organs; for liver biopsy, the presence of ascites is not a contraindication.
What complications can occur after image-guided biopsy of internal organs?
The following complications may occur after image-guided biopsy of internal organs:
- Hemorrhage, including severe hemorrhage during pancreatic biopsy
- Pneumothorax — after lung biopsy; also possible during liver biopsy
- Biliary peritonitis and hemobilia — during liver biopsy
- Bowel and gallbladder perforation — during liver biopsy
- Arterioportal shunt — during liver biopsy
- Post-procedural pancreatitis — in 3% of pancreatic biopsy cases
- Needle-tract tumor seeding — extremely rare
The source indicates that the overall complication rate of biopsy in general is less than 0.1%, and the mortality rate for liver biopsy is approximately 1:10,000.
The rule of doubt in staging: "When in doubt, choose the lower category." If the imaging findings are ambiguous, the patient is assigned the lower stage until definitive histological confirmation is obtained.
Class and exam questions
Is it possible to obtain multiple tissue samples with a single puncture?
Yes, the coaxial system allows the guiding cannula to be left in situ. Through it, an automatic cutting needle is introduced, making it possible to take biopsy samples at various angles without repeated tissue trauma.
Does the TNM stage change during the patient's treatment?
No, the TNM stage established before the initiation of therapy is recorded in the medical chart and remains unchanged throughout all subsequent treatment.
How to evaluate synchronous primary tumors?
If there are multiple tumors, the one with the highest T category is used for staging. If tumors are identified in paired organs, each is assigned a separate stage.
What else to study on this topic
- Clinical staging (cTNM) based on imaging data
- Pathomorphological staging features (pTNM)
- Impact of neoadjuvant radiation therapy on stage (y prefix)
- Historical classifications: Robson, Dukes', FIGO
- Principles of TNM stage grouping from 0 to 4
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