How do I correctly tattoo a sigmoid colon mass endoscopically for robotic resection, including whether to place the tattoo distal or proximal and whether to inject normal saline before injecting carbon‑based tattoo ink (e.g., SPOT)?

Endoscopic Tattooing for Sigmoid Mass Prior to Robotic Surgery

For a sigmoid mass requiring robotic surgical resection, place 2-3 tattoos at separate sites 3-5 cm DISTAL (anal side) to the lesion, first creating a saline bleb to confirm submucosal placement before injecting 0.75-1.0 mL of sterile carbon particle suspension at each site. 1

Critical Distinction: Surgical vs. Endoscopic Resection

The tattoo placement strategy differs fundamentally based on the intended intervention:

• For surgical resection (your scenario): The US Multi-Society Task Force on Colorectal Cancer recommends tattooing in line with the lesion AND on the opposite lumen wall to maximize visibility during laparoscopic/robotic surgery 1
• For future endoscopic resection: Tattoos should be placed 3-5 cm distal only, to avoid fibrosis that would complicate endoscopic removal 1

However, the distal placement at 3-5 cm remains the standard even for surgical cases in most recent guidelines, as this provides reliable localization without risking perilesional inflammation 1

Step-by-Step Tattooing Technique

1. Saline Bleb First (Safety Step)

• Always inject normal saline first using a 22-25 gauge needle to create a submucosal bleb 1
• This confirms you are in the correct submucosal plane and not transmural 1
• Once the submucosal plane is confirmed, exchange to the tattoo injection 1

2. Tattoo Injection Parameters

• Use sterile carbon particle suspension (e.g., SPOT) 1
• Inject 0.75-1.0 mL at each site 1
• Place 2-3 separate tattoos circumferentially 1

3. Location Relative to Lesion

• 3-5 cm distal (anal side) to the lesion 1
• The AGA 2024 guidelines specify tattoos should be placed at least 2 cm away from the lesion to avoid undermining fibroinflammatory response 1
• For surgical cases specifically, some sources recommend also tattooing the opposite wall at the same level for better intraoperative visualization 1

Critical Pitfalls to Avoid

Never Tattoo At or Proximal to the Lesion

• Tattooing at or near the lesion causes submucosal fibrosis that increases surgical difficulty and perforation risk 1
• A 2014 case report documented a colonic abscess requiring extended resection when tattoo was placed too close to the lesion 2

Avoid Transmural Injection

• Transmural injection can cause localized peritonitis, abscess formation, or inflammatory pseudotumor 1, 2
• The saline bleb technique prevents this complication 1

Document Everything

• Record tattoo location relative to the lesion in the endoscopy report (e.g., "3 tattoos placed 3 cm distal to lesion at 3,6, and 9 o'clock positions") 1
• Photo-document the tattoos in relation to the lesion 1
• Establish institutional standards for tattoo placement 1

Intraoperative Considerations

• Tattoos are visible laparoscopically in 88% of cases 3
• When tattoos are not visible (12-21.5% of cases), intraoperative colonoscopy may be required 4, 3
• Studies show tattoo localization is accurate in 69% of cases, with inaccuracy leading to surgical plan changes in 16% 4
• For sigmoid lesions specifically, distal tattooing provides reliable margins with mean deviation from target of only 0.33 cm 5

When Tattooing May Be Unnecessary

Tattoos are not required for lesions at clear anatomic landmarks 1:

• Cecum or adjacent to ileocecal valve
• Low rectum (within 5 cm of anal verge)
• Photo documentation with anatomic landmarks may suffice 1

Special Consideration for Complete Response Cases

If the patient receives neoadjuvant therapy and achieves clinical complete response, pre-treatment tattooing becomes critical for identifying the original tumor location and ensuring adequate distal margins 6