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CION Cancer Clinics
The parts of the liver, and why segments matter | CION Cancer Clinics
Doctors divide the liver into eight segments, each with its own blood supply and bile drainage. That is why a surgeon can remove one part and leave the rest working. When your report says a lesion is in segment seven, it tells you where it sits, not how serious it is. This page explains the main parts, the segment map, and why location shapes treatment. At CION Cancer Clinics in Hyderabad, our oncologists explain liver cancer in plain words and plan care around you and your family.
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Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed October 2026, next review due October 2027
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On this page
- What are the parts of the liver, and what is a segment?
- What are the main parts of the liver?
- Why does it matter which segment a tumour is in?
- How do I find where the tumour is on my report?
- Which operation removes which part of the liver?
- What do the anatomy words on a liver report mean?
- What this page cannot tell you
- Common questions about the parts of the liver
The short answer
What are the parts of the liver, and what is a segment?
Doctors divide the liver into eight segments, numbered one to eight. Each segment has its own blood supply and its own bile drainage, so a surgeon can remove one or several segments and leave the rest working. This system is called the Couinaud classification, after the surgeon who described it.
Which liver cancer this page is about
Segments matter for any tumour in the liver, but this page is written mainly for primary liver cancer, which starts in liver cells. If your report says "liver metastases", the cancer began somewhere else, and the two very different things called liver cancer explains how that changes the plan.
Why you are reading about this
Most people meet the word segment on a scan report: "a lesion in segment VII" or "lesions in segments IV and VIII". The number tells you where the tumour sits. It does not tell you how serious it is. Location matters because it decides which treatments can reach the tumour and how much healthy liver would be left behind.
Reports often use Roman numerals. Segment VII is simply segment seven.The big picture
What are the main parts of the liver?
Before the segments, it helps to know the larger parts they belong to.
The right liver
The larger half, sitting under the right ribs. It holds segments five, six, seven and eight. Many tumours are found here simply because it is the bigger part.
The left liver
The smaller half, reaching across towards the stomach. It holds segments two, three and four. Segments two and three together are often called the left lateral section.
The caudate lobe
Segment one. A small part at the back, wrapped around the main vein that carries blood back to the heart. Tumours here are harder to reach.
The hilum
The doorway on the underside where vessels and bile ducts enter and leave. A tumour near it can press on the bile ducts and cause jaundice.
What passes through it
- The portal vein, bringing blood from the gut
- The hepatic artery, bringing oxygen-rich blood
- The bile ducts, carrying bile out
Not sure whether this applies to you?
Ask an oncologistWhy the number matters
Why does it matter which segment a tumour is in?
The segment helps the tumour board decide what is possible. A small tumour on the edge of one segment may be removed with a small operation. The same tumour sitting deep, beside a major vein or near the hilum, may need a much larger operation, or a different treatment altogether.
It shapes surgery
Surgeons try to remove the tumour with its own segment, following the natural boundaries, so the remaining liver keeps its blood supply. What matters most is how much healthy liver stays behind. CION's surgical oncologists plan this with you, and your team will tell you where the operation takes place. Segmentectomy, lobectomy and extended resection explains the operations.
It shapes other treatments too
Ablation works best on tumours away from large blood vessels. TACE and TARE, which treat the tumour through its artery, can be aimed at one segment to spare the rest. CION coordinates these through accredited partner hospitals.
Who this does not suit
In a liver with cirrhosis, the health of the whole liver often matters more than the segment. A well-placed tumour may still not be safe to remove.
On your scan report
How do I find where the tumour is on my report?
Look for the word segment
It usually appears in the findings or the impression, written as a number or Roman numeral. Two numbers mean the lesion crosses a boundary.
Note right lobe or left lobe
Some reports use lobes instead of segments. The right lobe roughly means segments five to eight; the left lobe means two to four.
Check for vessels named nearby
Words such as portal vein, hepatic vein or hilum next to the lesion tell your doctor whether major vessels are close or involved.
Count the lesions
One lesion in one segment is a very different plan from several spread across both halves of the liver.
Take it to the person planning treatment
Write down your questions and bring the scan images, not just the report. The tumour board reviews the pictures themselves.
Leave a number, we will call you
One field. No form to fill in, and no charge for the call.
Side by side
Which operation removes which part of the liver?
Operation name
What is removed
Wedge or non-anatomical resection
The tumour with a rim of normal liver, ignoring segment lines
Segmentectomy
One whole segment, along its natural boundaries
Left lateral sectionectomy
Segments two and three
Left hepatectomy
The left liver, segments two, three and four
Right hepatectomy
The right liver, segments five to eight
Extended resection
One half plus part of the other, only when the liver is healthy
On your report
What do the anatomy words on a liver report mean?
- Couinaud segments
- The eight-part map of the liver that surgeons and radiologists use.
- Portal vein
- The large vein bringing blood from the gut into the liver. Tumour growing into it changes the treatment options.
- Hepatic veins
- The three veins draining blood out of the liver towards the heart. They mark the borders between sections.
- Subcapsular
- Just under the thin outer covering of the liver, near its surface.
- Exophytic
- Bulging outwards from the liver's surface rather than sitting deep inside.
- Future liver remnant
- The liver that would be left after surgery. It must be large and healthy enough to keep you well.
Being straight with you
What this page cannot tell you
It cannot tell you whether the lesion on your report is cancer. Many liver lesions are harmless, and the segment number says nothing about what a lesion is. Only the right scan, read by an experienced radiologist, and sometimes a biopsy, can answer that.
It cannot tell you which treatment suits you
The segment is one input among many. The tumour board also weighs the size and number of tumours, the blood vessels, how well the rest of the liver works and how fit you are. Two people with a tumour in the same segment can be offered very different plans.
Where to take your questions
If you have a report in hand and are unsure what it means, a CION oncologist can go through it and the images with you, and arrange any further scans through partner hospitals. How the liver works is a good place to start.
If you have been asked to have a follow-up scan, keep that appointment, whatever the segment.Questions we are asked
Common questions about the parts of the liver
How many segments does the liver have?
Eight, numbered one to eight in the Couinaud system. Segment four is sometimes split into an upper and lower part, written IVa and IVb. Each segment has its own blood supply and bile drainage, which is what makes it possible to remove one without damaging the others.
Is a tumour in segment seven or eight worse than elsewhere?
Not in itself. These segments sit high and at the back, under the diaphragm, so they can be harder to reach in surgery or ablation. That affects how a tumour is treated, not what kind of tumour it is. Your team will explain what the position means for you.
What is the difference between a lobe and a segment?
A lobe is a large part of the liver, such as the right or left lobe. A segment is a smaller unit inside a lobe, with its own blood supply. Surgeons plan operations by segments because those boundaries are where the liver can be divided safely.
Can I live with only part of my liver?
Yes, if the part left behind is healthy and large enough. A healthy liver regrows after surgery. A liver with cirrhosis regrows poorly, which is why surgeons check liver function and plan how much will remain before suggesting an operation.
Why does the report say the lesion is near the portal vein?
The radiologist is noting how close the lesion is to a major vessel. Being near the vein is different from growing into it. Either can change the treatment plan, so ask your doctor which one your report describes and what it means for the options.
Does it matter if lesions are in both halves of the liver?
It often does, because removing both would leave too little liver. Doctors may then combine treatments, stage the operation, or choose a treatment that reaches the whole liver. It does not automatically rule out treatment aimed at the tumours.
Do segments matter for cancer that spread from elsewhere?
Yes. Surgeons use the same map for secondary tumours, for example from bowel cancer. But the overall plan is led by the team treating the original cancer, and it follows that cancer's rules, not the rules for primary liver cancer.
Who can explain my liver scan in detail?
The radiologist who reported it, the surgeon or oncologist planning treatment, or a second opinion from a liver tumour board. Bring the images on a disc or link, not only the printed report. The CION helpline can arrange for an oncologist to go through them with you.
Your Specialists
Meet CION's liver cancer specialists. Bring your scan reports and liver blood tests.
Our medical and surgical oncologists plan liver cancer care together, weighing the tumour and how well your liver works before choosing surgery, a liver-directed procedure or medicines.
Medical Oncologist
Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
Medical Oncologist
Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
Medical Oncologist
Medical Oncologist
Surgical Oncologist
Dr. Muralidhar Muddusetty
MBBS (AIIMS), MS (Surgery) (AIIMS), DNB (Surgical Oncology), MRCS (Edinburgh)
Surgical Oncologist
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Sources
- Cancer Research UK — Surgery for liver cancer
- American Cancer Society — Surgery for Liver Cancer
- American Cancer Society — What Is Liver Cancer?
- National Cancer Institute — Liver Cancer Treatment
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
Related pages
How the liver worksWhat each part of the liver actually doesSegmentectomy, lobectomy and extended resectionThe operations built on the segment mapHow much liver can be safely removed?Why the part left behind matters mostLiver segmentectomy and wedge resectionThe surgical detail of removing one segment
Talk to us
Not sure what the segment on your report means?
Send us the scan report and images, and a CION oncologist will explain where the lesion sits and what that means for the next step. One helpline serves every CION centre.