Endoscopic mucosal resection — EMR

Endoscopic mucosal resection (EMR), also known as endoscopic mucosectomy, enables the removal of certain superficial lesions from the digestive tract using an endoscope. It is used in particular when the lesion requires a more extensive resection than a conventional polypectomy and shows no signs of deep invasion.

What is endoscopic mucosal resection?

The mucosa is the innermost layer of the wall of the digestive tract. When a lesion is confined to this area or to the most superficial layers, it may be possible to remove it from the inside using endoscopy without having to operate on the entire wall of the organ.

During an EMR, the specialist delineates the lesion and separates the tissue to be removed from the deeper layers. The resection may be performed in a single piece or, in the case of certain extensive lesions, in a planned manner in several fragments.

The excised tissue is collected and sent to the Pathology Department. Analysis of the tissue reveals the type of lesion that has been removed, assesses its depth, and determines whether the resection can be considered sufficient or whether further monitoring or additional treatment is required.

Why the depth of the lesion is a determining factor

A superficial lesion is one that appears to be confined to the inner layers of the digestive tract wall and shows no clear signs of deep invasion. This assessment is essential because size alone does not determine whether a lesion can be treated endoscopically.

A large lesion may still be superficial and suitable for EMR. Conversely, a smaller lesion may require a different approach if its appearance suggests that it has penetrated into deeper layers or if there is a significant risk of lymph node involvement.

The endoscopist examines the shape, margins, surface and vascular pattern using high-definition imaging systems. This characterisation enables an estimate of the depth to be made and guides the choice between EMR, ESD, other endoscopic techniques or surgery.

For which lesions can EMR be used?

EMR is mainly used for flat, sessile lesions or those larger than can be treated by conventional polypectomy, which show no clear signs of deep invasion.

In the colon and rectum, it is an important technique for numerous large, non-pedunculated superficial lesions and allows precursor tissue or certain very early-stage tumours to be removed endoscopically.

It can also be used for visible lesions associated with Barrett’s oesophagus. In this context, as well as treating the abnormal area, the resection provides tissue that allows for a more precise assessment of its nature and depth.

In the stomach, the choice between EMR and other techniques such as ESD depends particularly on the need to obtain a single specimen and on the characteristics of the lesion. For many selected gastric lesions, a technique that allows for a more comprehensive examination of the margins may be preferable.

In the duodenum, the indication requires particularly careful assessment because the wall is thinner and the risk of bleeding or perforation may differ from that seen in other locations.

How is it decided whether a lesion can be treated using EMR?

The decision begins with a detailed endoscopic assessment. The specialist assesses whether the lesion is well-defined, whether it appears superficial, whether it can be reached safely, and how it relates to the deeper layers.

The location, the presence of scarring, and any previous biopsies or treatments are also taken into account. Previous procedures may have caused fibrosis – that is, scar tissue that makes it difficult to elevate and separate the lesion from the deeper layers.

When a lesion appears complex and cannot be adequately treated during the initial examination, it may be preferable to document it and plan a specific session with a specialist in advanced endoscopy. This strategy helps to preserve the chances of a complete resection.

The selection process also takes into account associated conditions, the risk of bleeding, regular medication and the ability to provide follow-up care. The aim is not merely to assess whether the lesion can be technically resected, but whether EMR offers an appropriate strategy compared with other options.

Differences between EMR, polypectomy, ESD and surgery

These techniques can be used to treat gastrointestinal lesions, but they are not equivalent and are used in different situations.

Conventional polypectomy is usually used for small or pedunculated polyps that can be directly encircled with a snare and removed without extensive mucosal resection.

EMR is particularly indicated for certain flat, sessile or extensive lesions. It may allow for en bloc resection or, where the surface area is large, a planned removal in several fragments.

Endoscopic submucosal dissection (ESD) uses specialised instruments to progressively dissect the lesion and aims to facilitate en bloc resection where this offers a clinical advantage in terms of assessing margins and depth.

Surgery may be the most appropriate option when there are signs of deep invasion, a significant risk of lymph node involvement, or when a complete and sufficiently safe endoscopic resection is not feasible.

The choice is based on the actual characteristics of the lesion and not on one technique being generally superior to another.

Preparation before an EMR

When the lesion is located in the colon or rectum, proper bowel preparation is necessary. Thorough preparation allows the margins to be precisely defined, the resection to be carried out, and the treated area to be properly examined.

The hospital provides specific dietary guidelines and a laxative solution. These instructions must be followed as directed and must not be altered without authorisation.

When the lesion is located in the oesophagus, stomach or duodenum, the fasting instructions set out for the examination must be followed.

Prior to the procedure, any relevant medical conditions, allergies and regular medication are reviewed. Anticoagulant or antiplatelet treatments require individual assessment, as an EMR carries a different risk of bleeding compared to a diagnostic endoscopy. These medicines must not be stopped or altered without medical advice.

How an endoscopic mucosal resection is performed

EMR is performed using a flexible endoscope fitted with a camera and working channels. It is inserted via the mouth when the lesion is in the oesophagus, stomach or duodenum, and via the anus when it is located in the colon or rectum.

Once the area has been reached, the specialist carefully examines the surface, delineates the margins and confirms that the planned approach remains appropriate.

In conventional EMR, a solution is usually injected beneath the mucosa to elevate the lesion and create a separation plane from the deeper layers. A loop is then placed around the tissue and a controlled current is applied to complete the resection.

There are variants of EMR that can be performed without submucosal injection; therefore, this manoeuvre is not necessarily part of every procedure.

When the lesion is localised, it can be removed in a single piece. If it is more extensive, it can be resected in a planned manner in several fragments until all visible tissue has been removed.

Upon completion, the endoscopist inspects the treated area and controls any bleeding using clips, coagulation or other devices where necessary. In some locations, the mucosal defect may also be partially or completely closed to reduce certain subsequent risks.

The specimens retrieved are identified and sent to the Department of Pathology.

Sedation and immediate recovery

Sedation is tailored to the location, duration and complexity of the resection, as well as the patient’s clinical characteristics.

Breathing, heart rate, blood pressure and oxygenation are monitored throughout the procedure. Extensive or technically complex resections may require deep sedation and more direct involvement of .

Following a colorectal EMR, flatulence, a feeling of bloating or mild colic may occur. After a resection of the upper gastrointestinal tract, there may be throat irritation, mild discomfort when swallowing or nausea.

Recovery is monitored until the patient is awake and clinically stable. Whether the patient can be discharged or requires further observation depends on the extent of the resection and the immediate post-operative course.

Resection in a single piece or in several fragments

Removing a lesion in a single piece makes it easier for Pathology to examine the lateral and deep margins more accurately, as well as the relationship between the different areas of the lesion.

In certain large colorectal lesions, EMR may be planned to be performed in several fragments. This strategy allows extensive lesions to be treated endoscopically, although it limits the complete reconstruction of the margins under the microscope.

Fragmented resection also increases the likelihood that a small amount of tissue may remain on the scar. For this reason, it is usually accompanied by specific endoscopic follow-up.

What information does Pathology provide?

The removed tissue is examined under a microscope to identify the type of lesion, its degree of dysplasia and the possible presence of cancer.

Dysplasia describes abnormal changes in the cells and can be classified according to its grade. It does not in itself equate to invasive cancer.

When the resection is performed in a single piece, the laboratory can assess the depth and margins more reliably. In a fragmented resection, the nature of the tissue can be studied, but the complete reconstruction of the margins is more limited.

The histopathology report must be interpreted in conjunction with the endoscopic findings, the manner in which the resection was performed and the subsequent development of the scar.

Treatment outcomes and objectives

In appropriately selected lesions, EMR can achieve complete resection endoscopically and avoid the need for more extensive surgery.

This benefit is particularly relevant in certain large, superficial colorectal lesions. Not all resections, however, need to be completed in a single session.

When a lesion is removed in fragments, examination of the scar allows small residual areas to be detected and, in many cases, treated endoscopically.

In certain superficial lesions, EMR may constitute the definitive treatment when the resection and histopathological analysis meet favourable criteria.

If the examination reveals deeper invasion, insufficient margins or features associated with higher risk, further tests, a repeat endoscopic procedure or surgical assessment may be necessary.

Risks and potential complications depending on the lesion and the technique used

ERM is an endoscopic therapeutic procedure and may give rise to complications. The type and likelihood of complications depend on the location, size and characteristics of the lesion, the extent of the resection, the technique used and the individual’s clinical condition.

Bleeding may occur during the procedure or appear hours or days later. In many cases, it can be managed endoscopically, although some situations require hospital observation or further interventions.

Perforation is a tear in the wall of the digestive tract. Depending on its size, location and when it is detected, it may be treated using endoscopic instruments or may require surgery.

When an electric current is used, a thermal injury to the wall may also occur without a complete perforation. This situation can cause pain and fever and requires medical assessment.

Following extensive oesophageal resections, a stricture may develop; that is, a scar-induced narrowing that causes progressive difficulty in swallowing.

Sedation may also be associated with respiratory or cardiovascular complications. Continuous monitoring allows these problems to be detected and treated during the procedure.

The extent of the risk cannot be expressed as a single figure applicable to all ERM procedures. A small resection and an extensive procedure at a more complex site are clinically distinct procedures.

Recovery following an EMR

Many people are able to return home after a period of observation, although not all resections allow for discharge on an outpatient basis.

Where sedation is used, it is necessary to follow the instructions regarding accompaniment, driving and activities requiring caution in the hours following the procedure.

Diet and activity should be adapted to the area treated and the extent of the resection. Procedures involving the upper digestive tract may require a temporary diet, whilst extensive colorectal resections may necessitate limiting certain physical exertion.

In some situations, it may be preferable to extend the observation period or keep the patient in hospital, particularly where the resection has been complex, there is an increased risk of bleeding, or any complications arise.

Before discharge, the team provides personalised instructions on diet, medication, activity and symptoms that require assessment.

How follow-up and scar assessment are decided

The final plan is not determined solely on the basis of the findings obtained during the endoscopy. It takes into account the pathological findings relating to the treated organ, the size and characteristics of the lesion, and the manner in which the resection was performed.

Following a fragmented EMR of a large colorectal lesion, an early scar review is usually scheduled to confirm the absence of residual tissue and to treat any small remnants if necessary.

Lesions associated with Barrett’s oesophagus may also require treatment or monitoring of the remaining mucosa. Gastric and duodenal lesions follow their own criteria and should not be monitored by automatically applying the same intervals as those used for the colon.

When residual tissue is detected, it can often be treated during the follow-up endoscopy. If there is significant fibrosis, extensive recurrence or a lesion that is difficult to resect, it may be necessary to use a different endoscopic technique or to consider surgery.

What happens if the analysis identifies changes that require further assessment?

The histopathological examination provides a more precise understanding of the nature of the lesion and enables an assessment of whether the resection performed can be considered sufficient.

Where the analysis confirms that the lesion was superficial, has been adequately removed and does not present any high-risk characteristics, it may be sufficient to continue with the recommended endoscopic follow-up.

In other cases, the report may reveal changes that suggest the assessment should be supplemented with further tests or that it should be reviewed whether treatment needs to be extended. The decision depends on factors such as the depth of the lesion, the resection margins and other microscopic characteristics.

If cancer is identified, the result is assessed collectively by the team to determine the most appropriate next step. Depending on the specific characteristics, follow-up may be sufficient, a further endoscopic procedure may be required, or a surgical option may need to be considered.

Situations requiring specific assessment

Anticoagulant or antiplatelet therapy

These medicines may alter the risk of bleeding during and after ERM. Management is determined by jointly assessing the haemorrhagic risk of the resection and the risk of thrombosis associated with changing the treatment.

Lesions that have previously been biopsied or treated

Previous biopsies or procedures may cause fibrosis and affect the ability to elevate and resect the lesion. This information may influence the choice between EMR and other techniques.

Cardiac, respiratory, renal or hepatic diseases

Certain conditions may affect sedation, preparation and the observation period. Planning is adapted to the patient’s clinical condition and the complexity of the procedure.

Multiple lesions or family history

The presence of numerous lesions, an unusual age of onset or a relevant family history may warrant a specific assessment of hereditary risk and may alter the follow-up protocol.

Symptoms requiring medical assessment

Following an upper gastrointestinal endoscopy (UGIS), medical assessment should be sought in the event of heavy or recurrent bleeding, vomiting blood or black stools, particularly if accompanied by dizziness, weakness or loss of consciousness.

Severe or worsening abdominal, chest or neck pain, significant abdominal distension, fever, chills, persistent vomiting or difficulty tolerating fluids also require attention.

Following oesophageal resection, medical advice should also be sought if there is a progressive difficulty in swallowing. Severe breathing difficulties, loss of consciousness, heavy bleeding or a rapid deterioration in general health require urgent medical attention.

Specialists involved

ERM forms part of a care pathway that begins with the endoscopic characterisation of the lesion, continues with the selection of the resection technique, and concludes with histopathological analysis and follow-up of the treated area.

At the Publio Cordón Memorial Hospital, the Digestive Endoscopy Unit is the unit most directly involved in this treatment. It forms part of the Digestive System Department and carries out diagnostic and therapeutic endoscopy for general and complex digestive conditions. Its head, Dr Javier Aranda Hernández, specialises in the resection of early-stage tumours of the digestive tract and advanced therapeutic endoscopy.

The unit forms part of the Digestive System Department, which integrates clinical assessment with the various specialist units, enabling a decision to be made as to whether a lesion requires resection, monitoring or another form of treatment.

Pathology plays a key role following EMR, as tissue analysis determines the nature of the lesion, its depth and other factors that may alter the follow-up plan or necessitate a different therapeutic strategy.

When the analysis reveals a cancer with characteristics that may require further intervention, General and Gastrointestinal Surgery may be involved in the care pathway to assess surgical options.

In cases of extensive resections or where sedation is required, Anaesthetology and Intensive Care is involved in the assessment and monitoring during the procedure.

Not everyone requires the involvement of all these departments. The team adapts its approach based on the location and depth of the lesion, the technique used, the histopathological result and the possible need for endoscopic follow-up or further treatment.

Preguntas frecuentes

Are EMR and polypectomy the same thing?

Answer: Not exactly. Both are endoscopic techniques for removing lesions, but conventional polypectomy is usually used for certain polyps that can be resected directly using a snare. EMR allows for a more extensive resection of the mucosa and is used particularly for superficial lesions whose shape, size or extent require a different approach.

What is the difference between EMR and ESD?

Answer: EMR usually involves the use of a snare to remove the lesion and can be performed in a single piece or in several fragments. Endoscopic submucosal dissection (ESD) allows the lesion to be progressively separated from the deeper layers and facilitates en bloc resection when it is particularly important to assess the margins and depth accurately. The choice depends on the organ, the characteristics of the lesion and the benefits offered by each technique.

Does a serious injury always require surgery?

Answer: No. Size is only one of the factors taken into account. A large lesion may be confined to the superficial layers and suitable for endoscopic treatment, whilst a smaller one may require surgery if it shows signs of deep invasion or features associated with a higher risk.

Why can fluid accumulate beneath the injury?

Answer: In certain EMR techniques, a solution is injected into the submucosa to elevate the lesion and create a plane that facilitates its resection from the deeper layers. There are variants of EMR that do not require this injection; therefore, it is not a mandatory step in all procedures.

What does it mean that the lesion has broken up into fragments?

Answer: It means that the tissue has been removed in several pieces rather than as a single specimen. This approach may be appropriate for certain extensive lesions, particularly those of the colorectal tract, although it makes it difficult to assess the margins fully under the microscope and necessitates specific follow-up of the treated area.

Does a segmental resection mean that the EMR has failed?

Answer: No. In some large colorectal lesions, staged resection forms part of the strategy planned from the outset. Subsequent follow-up allows us to check that no residual tissue remains and to treat any small persistent areas if they are detected.

When is the scar checked following a fragmented EMR?

Answer: It depends on the organ, the size of the lesion and the type of resection. In the colon and rectum, following a segmental resection of a lesion measuring 20 millimetres or more, European guidelines generally recommend an early follow-up colonoscopy at 3–6 months. The specific interval is determined by the endoscopic and histopathological findings.

Can MRI tell us whether a lesion is cancerous?

Answer: The removed tissue is examined in the Department of Pathology and may reveal dysplasia, cancer and features relating to the depth of the lesion. When the resected tissue is obtained in a single piece, the assessment of the margins and depth is usually more comprehensive than when the sample is fragmented.

Is dysplasia a form of cancer?

Answer: No. Dysplasia refers to abnormal changes in cells and can be classified into different grades. It may indicate a higher potential for progression, but does not in itself equate to invasive cancer.

What happens if the test finds cancer?

Answer: The next step depends on the depth of invasion, the margins and other microscopic features relating to the risk of residual disease or lymph node involvement. In certain very superficial lesions that have been properly resected, endoscopic treatment may be sufficient; in others, further tests, another resection or surgery may be required.

Can any tissue remain after an EMR?

Answer: Yes, particularly following a resection involving several segments. Monitoring the scar enables the detection of small residual areas or local recurrences and, in many cases, allows these to be treated again using endoscopy.

Is an MRI scan always carried out under sedation?

Answer: Sedation is usually used, but the type and depth are tailored to the location of the lesion, the duration and complexity of the resection, and the patient’s clinical condition. Some more extensive procedures may require deep sedation or the specific involvement of the Anaesthesia team.

Is it necessary to stay in hospital after an EMR?

Answer: Not always. Some MRIs allow discharge after a period of observation, whilst others require prolonged monitoring or admission due to the extent of the resection, the location, associated conditions or any complications arising during the procedure. There is no single length of stay that applies to everyone.

What are the main risks associated with an EMR?

Answer: The risks depend on the location and extent of the lesion and the technique used. Complications to watch out for include bleeding, perforation, thermal injury and problems related to sedation. In certain extensive oesophageal resections, scar-induced narrowing may also occur, and following segmental resections there is a risk of residual tissue or local recurrence.

Can I stop taking anticoagulants or antiplatelet medication before an EMR?

Answer: They must not be discontinued or altered on one’s own initiative. EMR is considered a procedure with a significant risk of bleeding, and the team must jointly assess this risk alongside the risk of thrombosis associated with interrupting treatment. The management strategy depends on the medication, the reason for its use and the characteristics of the procedure.

Medical information for general guidance

This factsheet aims to help you understand what endoscopic mucosal resection is, for which lesions it can be used, how it differs from polypectomy and ESD, how the procedure is carried out, and what information the tissue analysis provides. It also explains why some lesions require a follow-up examination of the scar or additional treatment.

At the Publio Cordón Memorial Hospital, we believe it is important for medical information to be accurate, understandable and useful in guiding each individual through their care journey. Our specialists devote part of their work to explaining conditions, tests and treatment options in an accessible way, helping patients and their families to better understand each stage and participate with greater confidence in decisions about their health. This commitment to knowledge and public outreach is also part of our commitment to .

The information contained in this factsheet describes the general principles of EMR. The indication, resection technique and follow-up must be tailored to the depth, location and characteristics of the lesion, the pathological findings, any associated conditions and the available alternatives.