Extra-skeletal osteochondroma adjacent to the medial malleolus A case report

Abstract

The extra-skeletal osteochondroma is a rare clinical entity, only described as sporadic reports
in the medical literature. The usual clinical feature is a painless mass adjacent to a bone but not
having any connection with it. The osteochondroma is a closely resembling differential that has the
characteristic connection to the underlying bone appreciated in radiological assessment. We report
our experience with a case of a 19-year-old male patient with a painless lump over medial ankle
causing difficulty in wearing shoes. No functional impairment or distal neuromuscular deficit was
noted. The imaging revealed a well-defined, discrete ossified mass distal to the medial malleolus
and adjacent to the talus, having no connection with the underlying bones. Excision of the mass
led to the histopathological confirmation of the mass as an extra-skeletal osteochondroma. Despite being uncommon, extra-skeletal osteochondroma should be in the differential diagnosis of a well-defined solid lump with varying amount of calcification on the imaging. Excision biopsy, however,
has diagnostic and therapeutic value and usually is curative.

Keywords: Benign lesion, extra-skeletal osteochondroma, foot, lump, osteochondroma

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64 © 2023 Journal of the Uttaranchal Orthopaedic Association | Published by Wolters Kluwer - Medknow
Case Report
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DOI: 10.4103/juoa.juoa_3_23
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Abstract
The extra-skeletal osteochondroma is a rare clinical entity, only described as sporadic reports
in the medical literature. The usual clinical feature is a painless mass adjacent to a bone but not
having any connection with it. The osteochondroma is a closely resembling differential that has the
characteristic connection to the underlying bone appreciated in radiological assessment. We report
our experience with a case of a 19-year-old male patient with a painless lump over medial ankle
causing difculty in wearing shoes. No functional impairment or distal neuromuscular decit was
noted. The imaging revealed a well-dened, discrete ossied mass distal to the medial malleolus
and adjacent to the talus, having no connection with the underlying bones. Excision of the mass
led to the histopathological conrmation of the mass as an extra-skeletal osteochondroma. Despite
being uncommon, extra-skeletal osteochondroma should be in the differential diagnosis of a well-
dened solid lump with varying amount of calcication on the imaging. Excision biopsy, however,
has diagnostic and therapeutic value and usually is curative.
Keywords: Benign lesion, extra-skeletal osteochondroma, foot, lump, osteochondroma
Introduction
The extra-skeletal osteochondroma is
an unusual clinical entity presenting as a
benign mass lesion at various locations
including hand and feet region.[1] These
are extra-osseous or extra-synovial lesions
consisting of predominant mature hyaline
cartilage with an extensive enchondral
ossification.[2] These are discrete lesions
having no connection to the adjacent bone
unlike the osteochondroma or exostosis,
which are one of the commonest resembling
bone lesions. There are many hypotheses
regarding their formation but the exact
etiology is still unclear. Metaplasia of
mesenchymal fibroblast of the loose
connective tissues is one theory, whereas
other relates to their origin from pluripotent
cell lines from tenosynovium, synovium,
or other adjacent tissues.[3] Apart from it,
theories such as adipose tissue metaplasia
or association of repeated trauma as an
inciting event are also suggested. The usual
presentation is of a painless mass with or
without pressure effects on the adjacent
structures. These may be confused with
solitary osteochondroma, which chiefly
presents with painless growing mass with
location-specic symptoms and their painful
presentation is rarely encountered with
associated bursitis, fracture, or malignant
transformation.[4] The extra-skeletal lesions
are still not fully understood and limited to
sporadic care reports or small series in the
literature. Their presence as a mass at ankle
region is a rare occurrence.
CaseReport
A 19-year-old male presented to us with
an atraumatic swelling, noted over the
medial aspect of his right ankle for the
last 4 years. Initially, there was a history
of swelling being smaller in size before
it started growing slowly, but for the last
2years, the size has been relatively static.
There was a hard, nontender mass located
just below and anterior to the medial
malleolus with well-defined border and
irregular surface [Figure 1A and B]. There
was neither overlying skin problems nor any
raised temperature or overlying vascular
engorgement. The mass was not mobile
in any direction and underlying aspect of
the mass could not be palpated. There was,
Address for correspondence:
Dr. Ganesh Singh Dharmshaktu,
Department of orthopaedics,
Government Medical College,
Haldwani, Uttarakhand 263139,
India.
E-mail: drganeshortho@gmail.
com
Extra-Skeletal Osteochondroma Adjacent to the Medial Malleolus:
ACaseReport
How to cite this article: Dharmshaktu GS,
Agarwal N, Dharmshaktu IS, Pangtey T.Extra-
skeletal osteochondroma adjacent to the medial
malleolus: Acase report. J Uttaranchal Ortho Assoc
2022;1:64-7.
Received: 15-Feb-2023, Accepted: 02-Aug-2023,
Published: 09-Nov-2023
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GaneshSingh
Dharmshaktu,
Naveen Agarwal,
IshwarSingh
Dharmshaktu,
Tanuja Pangtey1
Departments of Orthopaedics
and 1Pathology and Blood Bank,
Government Medical College,
Haldwani, Uttarakhand, India
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Dharmshaktu, etal.: Extra-skeletal osteochondroma
65Journal of the Uttaranchal Orthopaedic Association | Volume 1 | Issue 2 | July-December 2022
Figure 1: The clinical image showing a lump over medial aspect of the
ankle adjacent to the medial malleolus (A and B) and the ankle radiographs
showing the presence of a well-defined mass below the medial malleolus
with calcification (C)
however, no interference with daily activities and the ankle
and toe movements were normal along with intact distal
neuromuscular status. The problem in wearing shoes was
the main concern of the patient because of the bumpy mass.
The ankle radiograph of the patient showed no signicant
bony abnormality except a heterogeneously calcied mass
present adjacent to the medial malleolus [Figure 1C]. The
lesion appeared well-dened and without any connection
to adjacent bones. The computerized tomography (CT)
scan of the ankle region better delineated the lesion [Figure
2A] as a discreet extra-skeletal mass adjacent to the medial
malleolus distally and medial to the talus bone. There was,
however, no bony connection noted with the underlying
bones [Figure 2B]. The excision biopsy of the lesion was
planned through an incision centered over the mass and
dissection of the skin and subcutaneous tissues revealed a
whitish capsule covering the mass lesion [Figure 2C and D].
The lesion was excised to reveal a solid, white mass with
irregular border measuring about 3 × 3× 2 cm [Figure 2E].
The mass was carefully dissected en bloc as it was loosely
adherent to the adjacent soft tissues. The wound was
closed in layers following a thorough lavage. No immediate
or remote postoperative complication or wound-related
problems were noted in the follow-up [Figure 3A]. The
biopsy results were suggestive of the presence of a lesion
composed of mature cartilage tissues with osteochondroma
as the histological diagnosis [Figure 3B]. On the basis of
clinicoradiological ndings, the nal diagnosis of an extra-
skeletal osteochondroma was made. No recurrence of the
lesion was noted in a follow-up of about 8months.
Discussion
The extra-skeletal osteochondroma presents as a
discrete, ossied mass within the soft tissues and may
need CT or magnetic resonance imaging (MRI) scans
for the diagnosis.[5] We also performed CT scan as the
patient could not afford MRI, and it delineated the
mass as separate entity from underlying bone and
exclude osteochondroma as differential. This is also
referred to as a variant of extra-skeletal chondroma, a
benign cartilaginous tumor with extensive enchondral
ossication.[2] Afew differential diagnoses need exclusion
like an acquired osteochondroma or Turret exostosis
that also presents like a mass besides the bone.[6] Usually,
these exostoses have posttraumatic history, which was
absent in our case. Benign parosteal osteochondromatous
proliferation or Nora’s lesion is a similar lesion along with
other mimics that resemble a mass similar to our case.[7]
Nora’s lesion presents with localized pain and swelling
with a cluster of variably calcied lesion. These also
do not have any connection with underlying bone, thus
providing a diagnostic dilemma only to be resolved by
histopathological conrmation. Histopathology in our
case was in favor of an osteochondroma.
Little is understood regarding etiopathogenesis of these
lesions. Afew articles, however, describe genetic involvement
or chromosomal rearrangements noted in association with
these lesions.[8] Usually, these lesions present as small
lumps but giant lesions are also reported. Occasionally,
the lesion may adapt to the shape of the underlying bone
and cover it like a hard shell without any clinical problem
other than apparent mass.[9] The diagnosis of extra-skeletal
osteochondroma requires clinical suspicion, knowledge
of the condition, judicious use of imaging modalities, and
histopathological correlation, like any other mass lesion.
These uncommon lesions require an acknowledgement for
early identication of the cases and robust studies to better
comprehend them for the optimal management.
Declaration of patient consent
The authors certify that they have obtained all appropriate
patient consent forms. In the form the patient(s) has/have
given his/her/their consent for his/her/their images and
other clinical information to be reported in the journal. The
patients understand that their names and initials will not
be published and due efforts will be made to conceal their
identity, but anonymity cannot be guaranteed.
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Dharmshaktu, etal.: Extra-skeletal osteochondroma
66 Journal of the Uttaranchal Orthopaedic Association | Volume 1 | Issue 2 | July-December 2022
Figure2: The CT images showing the lesion in details as a calcified mass medial to the talus and below the medial malleolus (A). The axial images showing
no connection of the lesion with the underlying bone (B). The intraoperative images showing the lesion covered with a thin capsule (C) overlying a solid,
white mass (D) that was excised en masse measuring about 3 × 3× 2 cm (E)
Figure3: The postoperative clinical image following the removal of the mass (A) and the histopathology image (B) showing the presence of a lesion laden
with mature cartilage tissue in the stroma (×40, hematoxylin and eosin)
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Dharmshaktu, etal.: Extra-skeletal osteochondroma
67Journal of the Uttaranchal Orthopaedic Association | Volume 1 | Issue 2 | July-December 2022
Financial support and sponsorship
Nil.
Conicts of interest
There are no conicts of interest.
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