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Health condition

Plexiform neurofibroma, how it is watched - and when treatment helps.

A benign nerve sheath tumour that is common in NF1 and usually best managed by an expert service. Most stay quiet - the skill is knowing which need treatment and which changes need urgent review.

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A radiographer guides a patient onto the bed of an advanced 3 Tesla MRI scanner in a London imaging suite

Why trust this guide

  • 01

    Editorial team

    Written by our editorial team from the UK sources listed on each page.

  • 02

    Sourced from guidance

    Checked against NHS England specialist commissioning, NICE and peer-reviewed sources you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK practice including MEK inhibitor therapy, whole-body MRI and NF1 specialist service pathways.

Key facts

Plexiform neurofibroma at a glance.

The essentials, in plain English - what it is, how it relates to NF1, and how it is managed in the UK today.

  • What it is

    A benign nerve sheath tumour that spreads along several fascicles or branches of a nerve, rather than forming a single discrete lump.

  • NF1 link

    Roughly 30 to 50% of people with neurofibromatosis type 1 (NF1) have one - and a plexiform neurofibroma is itself a recognised diagnostic feature of NF1.

  • When it appears

    Often congenital or arising in early childhood. Growth is usually most active in childhood, and some tumours are only found on imaging done for other reasons.

  • Why size matters

    Large lesions can disfigure, cause pain or weakness, and press on the airway, spinal cord or the tissues around the eye.

  • Malignant risk

    The lifetime risk of change into a malignant peripheral nerve sheath tumour (MPNST) is about 8 to 13% in NF1 - so most never do, but change must never be ignored.

  • Management

    Observation with expert review, selumetinib for eligible children, surgery where it is safe and useful, plus pain and psychosocial support.

Why this guide matters

Benign, but never to be ignored.

A plexiform neurofibroma can be harmless for decades or change a child’s life. The three points below shape everything else on this page.

  • Expert care changes outcomes

    These tumours are uncommon, so a specialist NF1 service that sees them regularly is the safest place to make decisions about scans, medicines and surgery.

  • New treatment options exist

    Selumetinib has changed what is possible for eligible children with tumours that surgery cannot fully remove - the conversation is worth having early.

  • Change is the signal

    New persistent pain, rapid growth, hardening or a new neurological deficit are what separate routine monitoring from an urgent review for malignant change.

How the diagnosis is made

From first swelling to a shared plan.

The steps a specialist NF1 team will normally follow, in order - so you know what to expect and why.

  1. 01

    Assessing

    History and examination

    When the swelling was first noticed, how it has changed, and whether there is pain, weakness or any pressure symptom.

  2. 02

    Assessing

    Look for wider NF1 features

    Cafe-au-lait patches, skin-fold freckling, other neurofibromas, eye findings and family history are all recorded.

  3. 03

    Assessing

    Referral to an NF1 service

    Because plexiform disease is best judged by people who see it often, a specialist NF1 service is involved early.

  4. 04

    Confirming

    MRI of the affected area

    Shows the extent of the tumour, its relationship to nerves, vessels, airway or spine, and whether pressure effects are present.

  5. 05

    Confirming

    Whole-body MRI for total burden

    Maps every plexiform lesion and allows volume to be measured, giving a baseline to compare against later scans.

  6. 06

    Planning

    PET-CT and biopsy if MPNST feared

    Reserved for suspicious change. PET-CT can highlight the most active area, and biopsy is planned through a specialist sarcoma team.

  7. 07

    Planning

    Multidisciplinary plan

    Genetics, paediatrics or neurology, surgery, pain and psychology agree a monitoring schedule and treatment options.

Typical timeline: specialist review and MRI within weeks - faster if there are urgent pressure or malignancy concerns.

Symptoms

What a plexiform neurofibroma can cause.

Effects depend far more on where the tumour sits than on its size alone - from a painless swelling to pressure on vital structures.

  • Diffuse soft swelling

    A soft, sometimes ropey enlargement that follows nerve pathways and is often present from early life.

  • Skin and tissue overgrowth

    Darker skin, thicker hair or overgrowth of the tissue over a tumour, and sometimes of the underlying bone.

  • Pain

    Aching, burning or shooting pain from stretched or compressed nerves - important to describe in detail.

  • Weakness or altered sensation

    Numbness, pins and needles or loss of strength in the area supplied by an involved nerve.

  • Airway and swallowing effects

    Tumours of the neck or upper chest can cause noisy breathing, sleep-disordered breathing or difficulty swallowing.

  • Spinal involvement

    Tumours along the spine can extend through the exit gaps of the nerves and press on the spinal cord.

  • Face, eyelid and orbit involvement

    Swelling around the eye or face that can affect the lid, the position of the eye and, at times, vision.

  • Red flag - rapid change

    Fast growth, new persistent pain or a hardening lump needs prompt specialist assessment.

Treatment

How plexiform neurofibroma is managed in the UK.

Observation for quiet tumours, selumetinib for eligible children, surgery where it is safe - and urgent action for pressure effects or suspected malignancy.

  • Observation with expert review

    Many plexiform neurofibromas cause few problems. Regular clinical review, with imaging when it is needed, is a legitimate plan.

  • Selumetinib (MEK inhibitor)

    An oral targeted medicine for children with NF1 and symptomatic plexiform neurofibromas that cannot be fully removed. Commissioned by NHS England and started only by a specialist service.

  • Surgery

    Considered for accessible tumours causing symptoms. Complete removal is often not possible because tumour and nerve are intertwined.

  • Partial debulking

    Reducing a tumour that presses on vital structures or disfigures. Bleeding can be significant and regrowth is possible, so surgery is carefully planned.

  • Urgent decompression

    Where a tumour threatens the airway, spinal cord or orbit, a rapid multidisciplinary decision on relieving pressure takes priority.

  • Pain management

    Nerve-pain medicines, physiotherapy and input from a pain team - see our pain management guide.

  • Psychosocial support

    Visible difference, long-term monitoring and childhood illness are demanding. Psychology and family support are part of good care.

  • Urgent MPNST pathway

    Suspected malignant change leads to rapid imaging, biopsy and referral to a specialist sarcoma team.

What this guide is based on

The sources behind every claim on this page.

UK national guidance and peer-reviewed research, current at the time of last review.

Key references

Guidelines and studies we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your NF1 specialist team knows the tumour, the scans and your history, and can tell you which parts apply to you. If something changes, get seen.

  • NHS England. Specialised commissioning for neurofibromatosis type 1 services, including selumetinib.

  • NICE. Selumetinib for treating symptomatic and inoperable plexiform neurofibromas in children with neurofibromatosis type 1 (technology appraisal).

  • MHRA. Selumetinib (Koselugo) product information and safety monitoring.

  • Gutmann DH et al. Neurofibromatosis type 1. Nature Reviews Disease Primers, 2017.

  • Gross AM et al. Selumetinib in children with inoperable plexiform neurofibromas. New England Journal of Medicine, 2020.

  • Evans DG et al. Malignant peripheral nerve sheath tumours in neurofibromatosis 1. Journal of Medical Genetics, 2002.

Red flags

When a plexiform neurofibroma needs urgent attention.

Most of the time these tumours are monitored calmly. These are the changes that should not wait for the next routine appointment.

  • Rapid growth

    A lump that enlarges over weeks or months, rather than slowly over years, needs prompt specialist review.

  • New, persistent pain

    Pain that is new, constant or wakes you at night - particularly in a previously painless tumour - is a recognised warning sign of MPNST.

  • Hardening of the tumour

    A soft lesion that becomes firm, hard or fixed to deeper tissue should be assessed without delay.

  • New neurological deficit

    New weakness, numbness or loss of function in the area supplied by an involved nerve.

  • Breathing or swallowing difficulty

    Noisy breathing, choking, voice change or new difficulty swallowing with a neck or chest tumour needs urgent assessment.

  • Spinal cord compression

    New back or neck pain with limb weakness, unsteady walking or bladder and bowel change is an emergency - seek immediate care.

  • Eye or vision change

    A swollen eyelid, a bulging eye or falling vision needs urgent ophthalmology review. In children with NF1, vision change can also signal an optic pathway glioma.

  • Sudden swelling or bleeding

    Abrupt painful enlargement or bruising can reflect bleeding into a vascular tumour and should be seen urgently.

  • Assuming it is just the known tumour

    Any change is worth reporting. Waiting to see if a familiar lump settles is the most common way malignant change is delayed.

Living with it

A long-term condition, with a team beside you.

Four things that make the biggest difference over the years - knowing your baseline, staying with a specialist team, looking after wellbeing and understanding the genetics.

A quiet reminder

Reporting a change is never wasting anyone’s time.

Most changes turn out to be benign, but early review is what keeps the rare serious ones treatable.

  1. 01 Monitor

    Know your baseline

    Photographs, measurements and a short symptom diary make real change easier to spot and easier to describe to your team.

  2. 02 Team

    Stay with a specialist service

    Plexiform disease changes over years. Ongoing multidisciplinary review, including a planned move from children’s to adult services, matters more than a single visit.

  3. 03 Support

    Look after the whole person

    School, work, body image and pain all shape daily life. Ask early for psychological support for the patient and the family.

  4. 04 Family

    Understand the inheritance

    NF1 can be inherited or arise new. Genetic testing and counselling explain what it means for relatives and future pregnancies.

Frequently asked

Everything we get asked about plexiform neurofibroma.

Quick answers on NF1, malignant risk, selumetinib and surgery.

  • What is a plexiform neurofibroma?

    A benign tumour of the nerve sheath that grows along several fascicles or branches of a nerve rather than as a single lump. It is strongly associated with neurofibromatosis type 1 and can range from a small area of thickened nerve to a large mass that affects function or appearance.

  • How common are they in NF1?

    Roughly 30 to 50% of people with NF1 have at least one. Many are present from birth or appear in early childhood, and some are only discovered on imaging carried out for another reason, so an internal tumour can exist without any visible sign.

  • Will a plexiform neurofibroma turn cancerous?

    Most will not. In people with NF1 the lifetime risk of a plexiform neurofibroma changing into a malignant peripheral nerve sheath tumour is estimated at about 8 to 13%. The warning signs are new persistent pain, rapid growth, hardening and new neurological deficit - and any of them should be assessed promptly.

  • Does every plexiform neurofibroma need treatment?

    No. If a tumour is not causing problems, careful observation with regular expert review is a sound plan. Treatment is considered when there is pain, loss of function, disfigurement or pressure on vital structures such as the airway, spinal cord or orbit.

  • What is selumetinib?

    Selumetinib is a MEK inhibitor - a targeted medicine taken by mouth that acts on the overactive signalling pathway driving these tumours. In England it is commissioned by NHS England for children with NF1 who have symptomatic plexiform neurofibromas that cannot be fully removed, and it is started and monitored by a specialist service. It does not suit everyone, and side effects need regular monitoring.

  • Why can’t surgeons simply remove it?

    Because the tumour is woven through healthy nerves and often lies close to blood vessels, complete removal can cause new nerve damage and heavy bleeding. Surgery is therefore usually partial, aimed at relieving a specific problem, and regrowth can occur - which is why it is planned by a specialist team.

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