Musculoskeletal clinical topic of the month – Peripheral Nerve Tumour presenting as shin pain

Peripheral nerve tumours

Peripheral nerve tumors (PNTs) are a heterogeneous group of mostly benign tumors that are rare in the general population. They usually develop in the peripheral nerve axonal nerve sheath and surrounding connecitive tissue. Although usually noncancerous, they still may require treatment because they can cause nerve compression, damage and/or loss of function.

Peripheral Nerve tumors can grow slowly or quickly, depending on the type. Some need no treatment or only monitoring. Rarely, nerve tumors are malignant and need aggressive treatment. Most of the time, nerve tumors are not linked to any known cause, but the risk of a PNT does increase if you have; 

  • Radiation therapy for other medical issues
  • Neurofibromatosis, a group of three nerve disorders

Neurofibromatosis types

Each type is linked to a different genetic defect. These defects can be inherited (passed down in families), or spontaneous (arising for unknown reasons).

  • Neurofibromatosis 1: This is the most common neurofibromatosis disorder, affecting up to about one in 3,000 Americans. It’s also known as NF1. It has a range of symptoms, including tumors that range from small nodules to large lumps. Most are benign tumors called neurofibromas.
  • Neurofibromatosis 2: This type, also called NF2, is linked to slow-growing nerve tumors called schwannomas. Schwannomas develop from the Schwann cells that form nerve sheaths. Most people with NF2 develop vestibular schwannomas — tumors on the vestibular nerves that link each inner ear to the brain — by age 30.
  • Schwannomatosis: This very rare neurofibromatosis disorder is linked to schwannomas that occur anywhere in the body except the vestibular nerve.

Case Presentation

Clinical history;

  • 24 year old recreational weight lifting
  • Started developing pain around inside of left thigh, lower leg and ankle for past three years ago
  • Described as a dull constant ache in inside leg
  • now had to markedly reduce exercise routines as very painful
  • Feels may have strained the area during a compound lift, but no obvious mechanism of injury
  • No bruising, swelling to the area of pain
  • Treated for tibialis posterior and achilles tendinopathy over the past few years but no real changes in symptoms
  • Sleep now disrupted, particularly when knees pressed together, therefore has to sleep with pillow between legs
  • No weight loss, no fever, no recent illness

Past Medical history;

  • BMI 22
  • Non-smoker
  • No history of ill health
  • No family history of poor health

Exercise history;

  • Recreational Olympic lifter
  • Good variation of training but now unable to perform most routine due to pain

Social history;

  • IT analyst
  • Non drinker or smoker

Clinical examination;

  • Mild non-specific tenderness across medial aspect of calf and shin
  • Tibialis Posterior activation pain free and strong
  • No myotomal or dermatomal deficit in right lower limb
  • No positive neural tension signs in lower back
  • Good pulses in foot and ankle
  • Very tender firm lump in medial thigh just superior to knee joint. Palpation and percussion of this lump reproduces local symptoms and referred pain down the medial shin (positive Tinel’s sign)

Clincial suspicions, differentials and reasoning;

  1. Peripheral Nerve tumour. The finding of a painful lump that refers pain down the leg on percussion is very suggestive of a nerve tumour. It is likely that his symptoms have been misdiagnosed as localised tendinitis and/or spinal pathology. 
  2. Spinal nerve root irritation. Unlikely as patient not had back pain and negative testing on lumbosacral neural sensitivity via slump and SLR with normal spinal examination
  3. Shin splints/Tibial stress. There could potentially be some tibial stress that has not been diagnosed, but this is unlikely given the lack of high impact training or other risk factors. Also no clinical palpable tendernes over the tibia. 
  4. Tibialis Posterior Tendinitis or calf muscle injury. Patient does not describe calf muscle injury or symptoms keep with tenditis such as localised swelling or stiffness. 

Imaging

Point of Care Ultrasound – Left ankle

Normal appearences of left tibialis posterior tendon and calf musculature. Mass in medial thigh showed sonographic appearences of a well cirumscribed 2cm x 2cm lesion adjacent to the gracilis muscle belly (left image). Lesion with neovascularisation (right image), suggestive of tumour (soft tissue or otherwise).

peripheral nerve tumour shin pain ultrasound

MRI

T2 shows 2cm x 2cm high signal lesion (with intrasubstance nerve bundles visible) adjacent to the saphenous nerve with appearences highly suggestive of Schwannoma. (Axial section left image, Coronal section right image)

peripheral nerve tumour shin pain mri

Diagnosis

Swannoma of saphenous nerve in left inner thigh causing local pain and referred pain down leg

Management

Medical

  • Patient put on anti-epileptic Pregabalin medication to reduce sensitivity of neuropathic pain as preliminary treatment
  • Patient referred to Perpheriphal Nerve Tumour unit for excision of lesion
  • Patient had only very mild ongoing symptoms post resection of tumour

Rehab

  • Desentisation programme for the of affected nerve lesion
  • Ongoing strength conditinoing training

Patient Self monitoring tools

  • LBSM pain and symptom diary
  • LBSM load monitoring diary

Key Summary and learning points

Peripheral Nerve Tumours

  • Beware of lumps and bumps that have neuropathic symptoms associated with them e.g. numbness, tingling, pain
  • Any nerve lesion can cause referred pain along is sensory distribution
  • Shin or Calf pain in particular can have neuropathic origins in the spinal or peripheral nerves. Always consider this if ongoing musculoskeletal management has failed
  • If imaging (MRI) has identified no spinal cause for lower limb neuropathic pain, always consider more distal lesions (e.g. pelvic, or local nerve lesions), neuropathies and demyelinating disease (e,g, multiple scelorsis)
  • Schwannomas are the commenest perhipheral nerve tumour and are usually benign in nature

Saphenous Nerve Anatomy

  • The saphenous nerve is the terminal branch of the femoral nerve. It travels within the subsartorial, or Hunter, canal with the femoral artery, exiting about 10 cm above the knee where it gives off an infrapatellar branch supplying the knee.
  • It then descends along the medial aspect of the tibia and medial malleolus.
  • The saphenous nerve provides sensory innervation to the medial aspect of the lower leg and the medial foot as far as the first metatarsal phalangeal joint.

Injury to the saphenous nerve

  • The nerve can be affected by injuries or procedures to the femoral artery such as catheterization within the subsartorial canal. It can also be injured as it exits the canal, particularly in individuals with genu valgus and internal tibia torsion because of exaggerated angulation as the nerve passes through the fascial layer.
  • At the knee, the saphenous nerve can be injured during arthroscopy or meniscectomy. An ill-fitting knee orthosis can cause focal compression. The infrapatellar branch of the saphenous nerve can be entrapped between the sartorius tendon and the medial femoral condyle causing anteromedial knee pain
  • In the lower leg, the nerve can be injured during saphenous vein harvesting for grafting or varicose vein stripping

Clinical presentation of saphenous nerve injury

  • Clinically saphenous neuropathy presents with sensory loss and occasionally significant neuropathic pain in the medial lower leg extending to the dorsum of the foot, sparing the toes.
  • Isolated infrapatellar branch injuries may cause medial knee pain that can be mistaken for pathology in the medial compartment of the knee. In pure saphenous nerve injury, there should be no motor weakness.
  • A Tinel sign may be elicited along the course of the nerve, and occasionally a neuroma may be palpated.
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