Bone & joints

Other chondrogenic tumors

Subungual exostosis


Editorial Board Member: Nasir Ud Din, M.B.B.S.
Deputy Editor-in-Chief: Borislav A. Alexiev, M.D.
Anshu Bandhlish, M.D.
Jose G. Mantilla, M.D.

Last author update: 7 January 2022
Last staff update: 8 February 2022

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PubMed search: Subungual exostosis[TI] full text[SB]

Anshu Bandhlish, M.D.
Jose G. Mantilla, M.D.
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Cite this page: Bandhlish A, Mantilla JG. Subungual exostosis. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/bonesubungualexostosis.html. Accessed May 18th, 2022.
Definition / general
  • Rare, benign osteocartilaginous lesion arising from the distal phalangeal bone below the nailbed
  • First described by Dupuytren in 1847
Essential features
  • Osteocartilaginous lesion involving the distal phalanx, lacking connection between the stalk of the lesion and medullary cavity of the native bone
Terminology
  • Dupuytren exostosis (not recommended)
ICD coding
  • ICD-O: 9213/0 - subungual exostosis (WHO Classification, page 345)
  • ICD-11: EE13.Y & XH1XL9 - certain disorders affecting the nails or perionychium & subungual exostosis
Epidemiology
Sites
Etiology
Clinical features
  • Most common clinical presentations include long standing pain (77%) followed by mass / swelling in the nail, nail changes such as erythema and deformity of the nailbed (Clin Orthop Relat Res 2014;472:1251)
  • Develops over a course of several months to years
Diagnosis
Radiology description
  • Pedunculated radiopaque mass on the dorsomedial aspect of the distal phalanx with nonaggressive growth
  • Lack of continuity between the lesion and the medullary cavity of the distal phalanx
  • Fibrocartilaginous cap appears hyperintense on T2 weighted images (Eur J Radiol 2019;112:93)
Radiology images

Contributed by Anshu Bandhlish, M.D. and AFIP images
Distal phalanx Xray Distal phalanx Xray Distal phalanx Xray

Distal phalanx Xray

Distal phalanx of great toe

Distal phalanx of great toe

Prognostic factors
  • Subungual exostoses are benign tumors
  • Local recurrence is seen in cases after incomplete excision in approximately 4% of cases (Clin Orthop Relat Res 2014;472:1251)
  • No malignant transformation or metastasis has been reported
Case reports
Treatment
Clinical images

Images hosted on other servers:
Subungual exostosis of index finger

Subungual exostosis of index finger

Subungual exostosis in an 8 year old child

Subungual exostosis in an 8 year old child

Subungual exostosis of right fifth toe

Subungual exostosis of right fifth toe

Gross description
  • Small bony and cartilaginous fragments
Microscopic (histologic) description
  • Peripheral fibrocartilaginous tissue with underlying stalk composed of trabecular bone, which is attached to the subjacent bone
  • Not continuous with the medullary cavity of the bone it arises from
  • Amount of cartilaginous tissue is determined by the age of the lesion
  • Early stage: cellular chondroid tissue with background proliferating fibrous tissue in the nailbed and may lack attachment to the underling phalangeal bone
  • Cartilaginous cap may show hypercellularity and atypia of the chondrocytes, with occasional mitoses; the cartilage matrix undergoes endochondral ossification over time
  • Late stage: eventually the lesion is composed of irregular trabecular bone with osteoblastic rimming with a thinned out or even absent cartilaginous cap (Czerniak: Dorfman and Czerniak's Bone Tumors, 2nd Edition, 2015)
Microscopic (histologic) images

Contributed by Robert Ricciotti, M.D. and AFIP images
Exophytic lesion of distal phalanx

Exophytic lesion of distal phalanx

Enchondral ossification

Enchondral ossification

Thin cartilaginous cap

Thin cartilaginous cap

Reactive bone Reactive bone

Reactive bone

Moderately cellular cartilage

Moderately cellular cartilage

Molecular / cytogenetics description
  • Consistently demonstrates t(X;6)(q24-26;q15-q25), associated with increased expression of IRS4 (insulin receptor substrate 4) gene
  • Fusion partners not fully characterized; however, COL12A1 is implicated in all cases described (Int J Cancer 2011;128:487, Int J Cancer 2006;118:1972)
Videos

What is a subungual exostosis?

Sample pathology report
  • Hallux, excision:
    • Subungual exostosis (see comment)
    • Comment: Osteocartilaginous lesion with a thin cartilaginous cap. Per imaging the lesion involves the distal phalanx of the great toe with lack of continuity with the medullary cavity of the underlying bone. Overall the morphology and the imaging findings are consistent with subungual exostosis.
Differential diagnosis
  • Osteochondroma:
    • Benign cartilaginous neoplasm with a cartilaginous cap
    • Medullary cavity of the stalk is continuous with that of the underlying bone
  • Florid reactive periostitis:
    • Mixture of reactive woven bone and fibrous tissue without zonation typically arising from the periosteum of fingers (commonly in the proximal phalanx)
  • Bizarre parosteal osteochondromatous proliferation ([BPOP] Nora lesion):
    • Surface osteocartilaginous lesion commonly develops in the proximal and middle phalanges of hands and feet
    • Long tubular bones can also be affected
    • Characteristic basophilic stroma at the interface of the bone and cartilage (blue bone) is identified
    • Balanced translocation t(X;6) seen in subungual exostosis is not reported in BPOP
    • Recurrent cytogenetic abnormalities described in BPOP include t(1;17)(q32;q21), inv(7) and inv(6) (Am J Surg Pathol 2004;28:1033, Virchows Arch 2005;447:99, Cancer Genet 2013;206:402)
Board review style question #1
Which bone is most commonly involved by subungual exostosis?

  1. Distal phalanx of the fingers
  2. Distal phalanx of the toes
  3. Middle phalanx of the toes
  4. Proximal phalanx of the fingers
Board review style answer #1
B. Distal phalanx of the toes

Comment Here

Reference: Subungual exostosis
Board review style question #2

Which of the following is true regarding subungual exostosis?

  1. Blue bone is a characteristic histologic finding
  2. Local recurrence may occur in approximately 30% of cases
  3. The marrow space of the stalk of the lesion communicates with the underlying bone
  4. There is no connection between the stalk of the lesion and medullary cavity of the native bone
Board review style answer #2
D. There is no connection between the stalk of the lesion and medullary cavity of the native bone

Comment Here

Reference: Subungual exostosis
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