Soft tissue

Other nonneoplastic

Morton neuroma



Last author update: 7 September 2023
Last staff update: 7 September 2023

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PubMed Search: Morton neuroma

Sabeehuddin Siddique, M.B.B.S.
Rola H. Ali, M.D.
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Cite this page: Siddique S, Ali RH. Morton neuroma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/jointsmortonsneuroma.html. Accessed April 15th, 2024.
Definition / general
  • Morton neuroma is a nonneoplastic, degenerative neuropathy with a strong predilection for the third interdigital nerve of the foot
  • One of the most common disorders encountered in the foot (Clin Radiol 2021;76:235.e15)
Essential features
  • Morton neuroma is a degenerative fibrotic neuropathy
  • Typically affects the interdigital nerve that innervates the third webspace (Radiographics 1999;19:1253)
  • Strong predilection for middle aged women (Foot Ankle 1983;3:238)
  • Characterized microscopically by nerve fiber degeneration and excessive intraneural and perineural fibrosis
  • Original series by Thomas Morton in 1876 (Am J Med Sci 1876;71:37)
Terminology
  • The term neuroma is a misnomer
  • Synonyms: interdigital neuroma, intermetatarsal neuroma, Morton metatarsalgia, plantar neuroma
ICD coding
  • ICD-10: G57.6 - lesion of plantar nerve, applicable to Morton metatarsalgia
Epidemiology
Sites
Pathophysiology
Etiology
  • Hyperextension of the toes by pointed, heeled shoes increases pressure on the forefoot and is implicated in nerve injury (J Foot Ankle Surg 1996;35:112)
Diagrams / tables

Contributed by Rola H. Ali, M.D.
Relevant anatomy for pathologists

Relevant anatomy

Clinical features
  • Sharp burning pain in the plantar aspect of the forefoot around the metatarsal heads and metatarsophalangeal joints that radiates to the toes (metatarsalgia) (Foot Ankle 1983;3:238)
  • Pain that is aggravated by walking and wearing tight shoes or high heels and alleviated by rest and removing the shoe
  • May be associated with numbness and the feeling of a pebble in the shoe (J Clin Orthop Trauma 2020;11:406)
  • Symptoms associated with larger size (AJR Am J Roentgenol 2000;175:649)
  • Smaller asymptomatic lesions may be relatively common with no gender predilection (Radiology 1997;203:516)
Diagnosis
Radiology description
Radiology images

Images hosted on other servers:
Morton neuroma on ultrasound

Ultrasound

Morton neuroma on MRI

MRI

Prognostic factors
Case reports
  • 30 year old man with history of traumatic little fingertip amputation and complicated surgeries developed fusiform enlargements of ulnar and radial proper digital nerves (Plast Reconstr Surg Glob Open 2022;10:e4035)
  • 46 year old woman with a 5 cm neuroma in the third webspace associated with macrodactyly and Raynaud phenomenon (Joints 2020;7:127)
  • 55 year old woman with neuroma of the proper digital branch of the fourth toe presented with isolated extreme fourth toe pain (Cureus 2020;12:e8920)
Treatment
Clinical images

Images hosted on other servers:
Exposing the neuroma - plantar approach

Exposing the neuroma - plantar approach

Exposing the neuroma - dorsal approach

Exposing the neuroma - dorsal approach

Large Morton neuroma

Large Morton neuroma

Gross description
  • Fusiform swelling of the nerve particularly at its bifurcation with adherence to fibrofatty tissue (Foot Ankle Int 2004;25:79)
Gross images

Images hosted on other servers:
Neuroma at the nerve bifurcation

Neuroma at the nerve bifurcation

Large resected neuroma

Large resected neuroma

Microscopic (histologic) description
Microscopic (histologic) images

Contributed by Rola H. Ali, M.D.
Nerve bundles

Nerve bundles

Perineurial fibrosis

Perineurial fibrosis

Arterial changes

Arterial changes

Perineurial and endoneurial fibrosis

Perineurial and endoneurial fibrosis

Concentric fibrosis

Concentric fibrosis

Vascular proliferation

Vascular proliferation


Nerve destruction

Nerve destruction

Hyalinization of endoneurial vessels

Hyalinization of endoneurial vessels

Accompanied synovial cyst

Accompanied synovial cyst

Synovial cyst close up

Synovial cyst close up

S100

S100

Trichrome stain

Trichrome stain


Virtual slides

Images hosted on other servers:
Morton neuroma

Morton neuroma

Positive stains
Electron microscopy description
Sample pathology report
  • Foot, excision:
    • Morton neuroma (see comment)
    • Comment: The histology shows degenerative fibrosing neuropathy consistent with Morton neuroma.
Differential diagnosis
  • Traumatic neuroma:
    • M = F, history of trauma or surgery
    • Location: may occur anywhere
    • Histology: numerous small nerve twigs
  • Localized neurofibroma:
    • M = F
    • Solitary lesions, mostly sporadic; multiple may be in NF1
    • Location: may occur anywhere, deep and superficial
    • Gross: when arising from a large nerve may look fusiform similar to Morton neuroma while cutaneous examples are not
    • Histology: mixed population of Schwann cells, fibroblasts, perineurial cells and occasional mast cells along with scattered axons and shredded collagen usually in a myxoid stroma
  • Plexiform neurofibroma:
    • M = F; arises early in life
    • Strongly associated with NF1
    • Location: may occur anywhere
    • Gross: tortuous nerve with a bag of worms appearance
    • Histology: expanded nerve branches with cytological features of conventional neurofibroma
  • Pacinian corpuscles and neuroma:
    • Corpuscles often encountered in tissue sections of Morton neuroma
    • Neuroma typically occurs on fingertips
    • Histology: hyperplasia of Pacinian corpuscles usually following trauma
  • Clinically, the differential may include intermetatarsal bursitis, rheumatoid arthritis, stress fracture and metatarsal / soft tissue tumors (Radiol Case Rep 2023;18:2416, Cureus 2022;14:e25305, Acta Biomed 2019;90:214)
Board review style question #1

A patient has been experiencing bouts of burning pain and numbness localized to the plantar aspect of the left forefoot at the level of the metatarsal heads. The pain is exacerbated by walking and relieved by rest and removal of the shoe. Excision shows the histology above. What is the diagnosis?

  1. Morton neuroma
  2. Pacinian neuroma
  3. Perineurioma
  4. Plexiform neurofibroma
  5. Traumatic neuroma
Board review style answer #1
A. Morton neuroma. The clinical presentation is typical. The histology image shows degenerative neuropathy with marked fibrosis and loss of nerve architecture. In contrast, all of the other answers are proliferative lesions. Answer B is incorrect because although a Pacinian corpuscle is seen on the right, there is no corpuscle proliferation. Answer C is incorrect because perineurioma of soft tissue is characterized by a proliferation of slender spindle cells with whorling. Answer D is incorrect because plexiform neurofibroma is composed of nerve bundles that are tortuous and expanded (as opposed to shrunken and fibrotic) by spindle cell proliferation. Answer E is incorrect because traumatic neuroma shows a haphazard proliferation of numerous nerve twigs.

Comment Here

Reference: Morton neuroma
Board review style question #2

A 45 year old woman has been experiencing bouts of pain in her left foot and has undergone a surgical procedure to remove the lesion. The histology of the lesion is shown above. Where did the lesion most likely arise from?

  1. First common plantar digital nerve
  2. Lateral plantar nerve
  3. Medial plantar nerve
  4. Proper plantar digital nerve
  5. Third common plantar digital nerve
Board review style answer #2
E. Third common plantar digital nerve. The picture shows a Morton neuroma, which classically affects the third common plantar digital nerve supplying the webspace between the third and fourth metatarsal heads. Answers A - D are incorrect because these nerves are not usually affected.

Comment Here

Reference: Morton neuroma
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