JBR–BTR, 2014, 97: 100-102.
NORA’S LESION OR BIZARRE PAROSTEAL OSTEOCHONDROMATOUS
PROLIFERATION: A RARE AND RELATIVELY UNKNOWN ENTITY
A. Rappaport1, A. Moermans2, S. Delvaux
3
The case of a 34-year-old man with a fast growing hard lump on the fourth digit of the right hand is presented. Radio­
graphy and MRI of the finger showed the radiologic characteristics of a bizarre parosteal osteochondromatous
­proliferation. Pathologic analysis confirmed the radiologic diagnosis.
Key-word: Osteochondromatosis.
Case report
A 34-year-old man was referred to
the radiology department by his generalist because of the presence of a
hard lump on the ulnar side of the
fourth finger of the right hand. The
patient had felt this lump a couple of
weeks after suffering a crush injury
of his finger.
A radiography (Fig. 1) showed the
presence of a parosteal flamelike
bony proliferation or calcification,
extending from the middle phalanx
of the fourth digit on the ulnar aspect.
The bony proliferation or calcification was surrounded by a nodular
soft tissue swelling.
A control radiography (Fig. 2) was
performed after 3 months and showed
that the bony proliferation had clearly enlarged and had grown out into a
mature bony mass.
An MRI (Fig. 3) was performed to
evaluate the soft tissue component
of the mass.
Because the lump was bothering
the patient, it was surgically excised.
Pathological analysis (Fig. 4)
­confirmed this lesion was a bizarre
parosteal osteochondromatous proliferation.
Discussion
General features
Bizarre
parosteal
osteochondromatous proliferation (BPOP) is
part of a spectrum of reactive lesions. Florid reactive periostitis, one
can consider the first stadium, followed by BPOP and turret exostosis
(reactive osteochondroma) as end
stage (1).
BPOP was first described by Nora
in 1983 and is frequently referred to
as Nora’s lesion (2).
Fig. 1. — Radiograph shows a flamelike
parosteal calcification/ossification extending from the middle phalanx of the fourth
digit on the ulnar aspect (arrow). This calcification/ossification is surrounded by a
nodular soft tissue swelling.
From: Department of 1. Radiology, 2. Orthopaedic Surgery, 3. Pathology, Sint-Trudo
Ziekenhuis, Sint-Truiden, Belgium.
Address for correspondence: Dr A. Rappaport, M.D., Department of Radiology, STZH,
Diestersteenweg 100, 3800 Sint-Truiden, Belgium. E-mail: [email protected]
rappaport-.indd 100
Fig. 2. — A control radiography after
3 months shows that the bony proliferation had clearly enlarged and has grown
out into a mature bony mass. There
seems to be a discrete cleavage plane
between the lesion and the underlying
­
cortex and there is no evidence of medullary continuity.
It is defined as a “well-marginated
mass of heterotopic mineralization
arising from the periosteal aspect of
an intact cortex without medullary
changes” (3).
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101
A
Fig. 4. — Light micrographs (H&E, ×10 obj) shows lobulated
hypercellular cartilaginous tissue (A), calcified fibrocartilaginous
tissue (B) and focal basophilic calcification (C).
B
Patients in the fourth decade tend
to be more affected. In contrary osteochondromas appear more commonly in the second and third decades. The age range can be quite
large, so age can’t be used as a correct discriminator (4).
Imaging features
C
Fig. 3. — MRI shows that the lesion (arrowhead) is nodular and has no contact
with the medullary bone. Coronal T1
weighted images show the lesion is T1hypointense (A). This lesion shows
marked, especially peripheral, contrast
enhancement (B). Axial T2 weighted images with fat suppression show that the
lesion is homogeneous T2-hyperintense
(C).
BPOP is most frequently found in
the hand, more specifically at the diaphysis of the phalanges (proximal
phalanges more affected than distal
phalanges). Since these lesions are
also more often found at the right
hand side, some authors expect traumatic events could be at the origin of
BPOP (3).
Men are more frequently affected
than women by BPOP and this feature could support the theory of possible traumatic origin of the lesion (3).
rappaport-.indd 101
On radiography, the appearance
of BPOP is dependant on the stage of
evolution of the lesion. The first
stage presents as a periosteal soft
tissue swelling with or without the
presence of small amount of calcifications. In later stages the soft tissue
mass progressively calcifies and finally ossifies. This evolution from
soft tissue mass to ossified mass
takes approximately 6 months (3).
As mentioned above, the mass arises from the periosteal aspect of the
intact cortex of diaphysis or metaphysis and generally there isn’t continuity with the medulla. The mass
can be pedunculated or sessile and
usually there is a cleavage plane between the lesion and the underlying
cortex. Periosteal reaction is absent (5).
CT is better than plain radiograph
in detecting the possible connection
with the medullary bone (4).
MRI presents nonspecific features. It is solely useful in differentiating with an osteochondroma and
evaluating the extent of the soft tissue component.
In differentiating MRI can evaluate
the continuity of the lesion with the
medulla and can confirm the ab-
sence of the cartilage cap, which is
present in osteochondroma. In general the mass has a low to intermediate T1-weighted signal and a high to
intermediate T2-weighted signal, depending on the amount of the cartilage component. After the administration of gadolinium contrast, the
lesion shows marked enhancement (4). These signal characteristics are nonspecific and can appear
in a fare amount of benign and malignant lesions.
Differential diagnosis
Because of its localization and
­ ppearance BPOP is often misdiaga
nosed as an osteochondroma. As
mentioned above, BPOP isn’t in continuity with the medulla as an osteochondroma is. Exceptional cases of
BPOP do show continuity, what
makes differential diagnosis difficult.
BPOP also lacks the orientation away
from the physis as an osteochondroma has. As mentioned above, BPOP
also lacks the presence of a cartilage
cap (4).
Pathologic analysis can make definite distinction between the two. Differentiation between these two lesions is important, as BPOP needs a
more aggressive surgical resection
as it has a higher recurrence rate (4).
Also differential diagnosis with
malignant lesions as periosteal/parosteal chondrosarcoma and osteosarcoma can be made. A parosteal
osteosarcoma rarely appears in the
hands and both lesions have a more
aggressive radiologic appearance
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and are frequently accompanied by
cortical invasion, soft tissue invasion
and periosteal reaction (3).
Juxtacortical chondromas mostly
arise metaphyseally whereas BPOP
mostly arise diaphyseally, but this is
not considered a reliable discriminator. A juxtacortical chondroma shows
a soft tissue component and matrix
calcifications as seen in early stage
BPOP, but usually cortical scalloping, cortical irregularities and periosteal reaction are present, that are not
found in BPOP (5).
Myositis ossificans appears in
contrary to BPOP in larger muscles
and ossifies from peripheral to central (5).
Pathological analysis
Pathological appearance reflects
the radiographic appearance of the
BPOP lesion. It can perfectly depict
all the components of the lesion: cartilage, fibrocartilaginous tissue, calcification and immature bone.
Florid reactive periostitis, considered as the first stage of “reactive lesions”, is composed of spindle cells
with minimal osteocartilaginous proliferation. When bone and metaplastic cartilage become a prominent factor, the lesion is considered a BPOP.
The cartilage can be regulary or
irregulary arranged and can show
­
variable grade of bony mineralization. As the ossification matures and
a cartilage cap is formed, the lesion
rappaport-.indd 102
JBR–BTR, 2014, 97 (2)
is considered a Turret exostosis (acquired osteochondroma).
Typically for BPOP is that the cartilaginous layers are hypercellular
and that the chondrocytes are disorganised and show cytologic atypia
(enlarged nuclei,…). Histologically,
the appearance of these chondrocytes can mimic the histologic appearance of a chondrosarcoma.
The fibroblastic spindle cells can
also show atypia.
The bone appears also disorganized and can present spindle shaped
fibroblasts in the intertrabecular
spaces
Fibroblastic tissue and the chondrocyte atypia is not present in an
osteochondroma (4).
Management/therapy ?
BPOP has a characteristic radiologic appearance, so differentation
with malignant lesions is not difficult. Biopsy therefore is rarely indicated.
If resection is not immediately
considered, a control radiography is
suggested after 6 months to evaluate
the natural evolution.
Golden standard for the treatment
of BPOP is surgical excision. BPOP
has a high recurrency rate (20-55%).
For decreasing the recurrency rate,
wide excision including excision of
the underlying periostal tissue and
pathological cortex is advised (4).
Conclusion
BPOP or Nora’s lesion is part of a
spectrum of reactive lesions. It is a
rare entity with a characteristic
radiologic appearance. Especially
­
plain radiograph gives the clue to the
diagnosis.
Radiologists should know this
­entity because correct diagnosis and
differentiation with osteochondroma
is important for the surgical approach.
References
1. Dorfman H.D., Czerniak B.: Bone
­Tumors. St. Louis, MO: Mosby, 1998.
2. Nora F.E., Dahlin D.C., Beabout J.W.:
Bizarre parosteal osteochondromatous proliferations of hand and feet.
Am J Surg Pathol, 1983; 7: 245-250.
3. Dhondt E., Oudenhoven L., Khan S.,
Kroon H.M., Hogendoorn P.C.,
Nieborg A., Bloem J.L., De ­Schepper A.:
Nora’s lesion, a distinct radiological
entity? Skeletal Radiol, 2006 35: 497502.
4. Chamberlain A.M., Anderson K.L.,
Hoch B., Trumble T.E., Weisstein J.S.:
Benign Parosteal Osteochondromatous Proliferation of the Hand Originally Diagnosed as Osteochondroma:
A Report of Two Cases and Review.
Hand (NY), 2010, 5: 106-110.
5. Kransdorf M.J., et al.: Extraskeletal
osseous and cartilaginous tumors.
Imaging of Soft Tissue tumors. 2nd
ed. Philadelphia: Lippincott Williams
& Wilkins, 2006: 449-452.
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