Bone & joints
Other chondrogenic tumors
Subungual exostosis
Authors: Anshu Bandhlish, M.D., Jose G. Mantilla, M.D.
Editorial Board Member: Nasir Ud Din, M.B.B.S.
Deputy Editor-in-Chief: Borislav A. Alexiev, M.D.
Last author update: 7 January 2022
Last staff update: 8 February 2022
Copyright: 2003-2023, PathologyOutlines.com, Inc.
PubMed search: Subungual exostosis[TI] full text[SB]
Table of Contents
Definition / general | Essential features | Terminology | ICD coding | Epidemiology | Sites | Etiology | Clinical features | Diagnosis | Radiology description | Radiology images | Prognostic factors | Case reports | Treatment | Clinical images | Gross description | Microscopic (histologic) description | Microscopic (histologic) images | Molecular / cytogenetics description | Videos | Sample pathology report | Differential diagnosis | Additional references | Board review style question #1 | Board review style answer #1 | Board review style question #2 | Board review style answer #2Cite this page: Bandhlish A, Mantilla JG. Subungual exostosis. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/bonesubungualexostosis.html. Accessed January 30th, 2023.
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
Epidemiology
- Adolescents and young adults
- More than 50% of cases are in patients younger than 18 years (average age: 25.7 years) (Clin Orthop Relat Res 2014;472:1251)
- M:F = 1:1 (Clin Orthop Relat Res 2014;472:1251)
Sites
- Toes most frequently involved (80% involve the first toe) (Clin Orthop Relat Res 2014;472:1251)
- Fingers rarely involved (Pediatr Investig 2020;4:292)
Etiology
- Unclear
- Preceding trauma and infection have been reported in 29% and 14% of cases, respectively (Clin Orthop Relat Res 2014;472:1251)
- Presence of t(X;6)(q24-q26;q15-q25) rearrangement suggests this is a true neoplastic process (Int J Cancer 2011;128:487)
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
- Radiological and pathological correlation is recommended
- Limited biopsy samples from the periphery of the lesion may create an impression of a malignant cartilaginous neoplasm
- Reference: Czerniak: Dorfman and Czerniak's Bone Tumors, 2nd Edition, 2015
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 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
- 7 year old boy with subungual exostosis of the index finger (Indian J Dermatol Venereol Leprol 2018;84:232)
- 8 year old boy and 36 and 37 year old women in 3 cases of subungual exostosis with different clinical presentations (Skin Appendage Disord 2016;1:213)
- 65 year old woman with subungual exostosis of left long finger (Iowa Orthop J 2013;33:228)
Treatment
- Complete marginal excision with minimal trauma to the nailbed is the optimal treatment (Clin Orthop Relat Res 2014;472:1251, J Pediatr Orthop B 2020;29:382)
Clinical images
Images hosted on other servers:
Subungual exostosis of index finger
Subungual exostosis in an 8 year old child
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
Enchondral ossification
Thin cartilaginous cap
Reactive bone
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)
Additional references
Board review style question #1
Which bone is most commonly involved by subungual exostosis?
- Distal phalanx of the fingers
- Distal phalanx of the toes
- Middle phalanx of the toes
- Proximal phalanx of the fingers
Board review style answer #1
Board review style question #2
Which of the following is true regarding subungual exostosis?
- Blue bone is a characteristic histologic finding
- Local recurrence may occur in approximately 30% of cases
- The marrow space of the stalk of the lesion communicates with the underlying bone
- 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
Comment Here
Reference: Subungual exostosis
