🧬 TOACS FCPS Station · Plexiform Neurofibroma in Neurofibromatosis

Nelson · 22nd Ed · · “Diffuse, infiltrating benign nerve sheath tumors; congenital; hallmark of NF1; risk of MPNST; FDA-approved selumetinib (MEK inhibitor) for inoperable symptomatic lesions”
⏱️ 7 minutes · Examiner-led · Observed station
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📷 Clinical Photograph – Plexiform Neurofibroma

Clinical photograph showing a large, diffuse, infiltrative plexiform neurofibroma on the neck and face of a child with neurofibromatosis type 1
Figure 1 · Plexiform Neurofibroma · Neurofibromatosis type 1 (NF1)

🔍 Key clinical features:

  • ✓ Diffuse, infiltrating mass – often present at birth or early childhood
  • ✓ Soft, "bag of worms" texture – palpable along nerve bundles
  • ✓ May involve any nerve – commonly cervical, facial, lumbosacral, mediastinal
  • ✓ Hyperpigmentation (cafe-au-lait) – overlying skin
  • ✓ Can cause disfigurement, pain, functional impairment
  • ✓ Risk of malignant transformation – to MPNST (malignant peripheral nerve sheath tumor)

📋 Clinical scenario (examiner prompt)

A 9‑year‑old child with a known diagnosis of neurofibromatosis type 1 (NF1) is brought in due to a rapidly enlarging mass on the left arm The mother reports that the mass has been present since birth but has increased in size over the past 3 months and is now associated with severe pain and limited movement. On examination, there is a large, diffuse, soft, infiltrating mass extending from the arm to the forearm, with overlying hyperpigmented skin. The child has multiple cafe‑au‑lait spots and axillary freckling.

Rapidly enlarging neck mass Severe pain, limited movement Diffuse, infiltrating lesion NF1 with CALs, axillary freckling

🧑‍⚕️ Examiner tasks · TOACS

1. Identify the diagnosis from the clinical image and context.

2. Describe the clinical features (plexiform neurofibroma – diffuse, infiltrating mass, soft consistency, overlying hyperpigmentation).

3. Explain the underlying condition (NF1, NF1 gene mutation, neurofibromin, Ras pathway).

4. Discuss complications and management (MPNST risk, imaging, selumetinib, surgery, surveillance).

⚠️ Key concept: A plexiform neurofibroma is a congenital, diffuse, infiltrating tumor of the peripheral nerve sheath, pathognomonic for neurofibromatosis type 1 (NF1). Rapid growth, new or worsening pain, and neurologic deficit should raise concern for malignant transformation to MPNST (malignant peripheral nerve sheath tumor). Imaging (MRI with contrast, PET/CT) and biopsy are indicated. Selumetinib (MEK inhibitor) is FDA‑approved for inoperable symptomatic plexiform neurofibromas. Complete surgical resection is the goal but often not possible due to infiltration.

🎯 Expected answers (for examiners)

  • • Diagnosis: Plexiform neurofibroma in NF1 (with concern for malignant transformation to MPNST)
  • • Clinical features: Diffuse, infiltrating, soft "bag of worms" mass along nerve; often present at birth; overlying skin hyperpigmentation (CAL); may cause pain, disfigurement, functional impairment
  • • NF1 diagnosis: ≥2 of: CALs (≥6), axillary/inguinal freckling, neurofibromas (≥2) or 1 plexiform, optic glioma, Lisch nodules, sphenoid dysplasia/tibial pseudarthrosis, first-degree relative, NF1 pathogenic variant
  • • MPNST suspicion: Rapid growth, new or worsening pain, neurologic deficit, PET/CT uptake (SUVmax >3)
  • • Imaging: MRI (to assess extent, infiltration), PET/CT (for malignant transformation)
  • • Treatment: Selumetinib (MEK inhibitor) for inoperable symptomatic plexiform neurofibromas; surgical resection if feasible; chemotherapy for MPNST
  • • Surveillance: Annual ophthalmology, BP monitoring, developmental screening, and routine physical exam for new/changing lesions
📌 Plexiform neurofibroma – key points:
• Incidence: ~30% of NF1 patients, usually congenital
• Location: Head/neck (20%), trunk, extremities, lumbosacral
• Risk of MPNST: 8-13% lifetime risk (most common cause of death in NF1)
• Red flags: Rapid growth, persistent pain, neurologic deficit
• FDA-approved therapy: Selumetinib (MEK inhibitor) for inoperable symptomatic lesions
• Surgical considerations: Complete resection often difficult (infiltrating); debulking for cosmesis or symptom relief

⚡ Quick FCPS‑style MCQ

A 6-year-old with NF1 presents with a rapidly enlarging, painful neck mass with overlying hyperpigmentation. The most concerning complication is:

A. Benign growth of cutaneous neurofibroma B. Malignant transformation to MPNST C. Spontaneous regression D. Reactive lymphadenopathy

📌 Topic summary · Plexiform Neurofibroma in NF1

Definition
Diffuse, infiltrating nerve sheath tumor
Associated with
Neurofibromatosis type 1 (NF1)
Risk
Malignant transformation to MPNST (8-13%)
Red flags
Rapid growth, pain, neurologic deficit
Imaging
MRI, PET/CT for malignancy
Treatment
Selumetinib, surgery, surveillance
FeaturePlexiform Neurofibroma
OnsetCongenital (present at birth or early childhood)
AppearanceDiffuse, infiltrating, soft ("bag of worms"), overlying CAL
NF1 associationDiagnostic criterion (≥1 plexiform neurofibroma)
MPNST risk8-13% lifetime risk; most common cause of death in NF1
ImagingMRI for extent; PET/CT (SUVmax >3 suggestive of malignancy)
TreatmentSelumetinib (MEK inhibitor) for inoperable symptomatic lesions; surgical resection (partial/debulking); MPNST: chemotherapy, radiation, surgery
SurveillanceAnnual ophthalmology, BP, developmental screening, physical exam; MRI if symptoms
Source: Nelson Textbook of Pediatrics 22nd Ed · : Neurofibromatosis · TOACS FCPS station.