Bizarre Parosteal Osteochondromatous Proliferation of the Skull in a Young Male

doi:10.4236/ojrad.2013.33022

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Open Journal of Radiology, 2013, 3, 133-135

http://dx.doi.org/10.4236/ojrad.2013.33022 Published Online September 2013 (http://www.scirp.org/journal/ojrad)

Bizarre Parosteal Osteochondromatous Proliferation of

the Skull in a Young Male

Radu Baz, Cosmin Niscoveanu*

Pozitron Medical Investigations, Constanta, Roma nia

Email: *[email protected]

Received August 1, 2012; revised January 2, 2013; accepted January 9, 2013

License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

ABSTRACT

Bizarre parosteal osteochondromatous proliferation (BPOP), as defined by Nora and colleagues in 1983 (also called

Nora lesion), is a rare lesion. About 160 cases of BPOP have been presented in the literature to date. The lesion is an

exophytic outgrowth from the cortical surface consisting of bone, cartilage and fibrous tissue. These types of lesions

have been reported mostly in the hands and feet. Localization at the level of the skull is extremely rare. We report a case

of a young man with multiple Nora’s lesions with atypical localization in the skull and mandible.

Keywords: BPOP; Nora; CT; Skull

1. Introduction

Nora’s lesion, also called bizarre parosteal osteochon-

dromatous proliferation (BPOP), is a rare benign osseous

tumor that presents exophytic cortical growth consisting

of bone, cartilage, and fibrous tissue. It was first de-

scribed by Nora and colleagues in 1983 [1]. It usually

affects the proximal and middle phalanges, and the

metacarpal or metatarsal bones. The hands are 4 times

more commonly affected than the feet; however, lesions

in other bones have been reported [2-4]. It usually affects

patients in their 20s or 30s, with no sex predilection. This

benign lesion can be mistaken for malignant processes

because of the high frequency of recurrence, the potential

rapid growth and atypical histologic appearance. We

report a case of a young man with multiple Nora’s le-

sions with atypical localization in the skull and mandi-

ble. From our knowledge this is the second case in the

literature with BPOP in the mandible [5], and also we did

not encounter other cases with such a spreading in the

skull and jaw.

2. Case Report

A 22-years old male was referred to our imaging center

for a computed tomography of the skull for paro tid space

masses which appeared a few months ago, being more

painful in the last weeks. He also reported a recent in-

crease in the size of the masses. At clinical examination,

the patient presented with mildly painful swelling at the

level of parotid and submandibular space, bilaterally.

Palpation revealed hard masses, 3 - 5 cm in diameter,

immobile, with irregular surface, more proeminent on the

left. The overlyin g skin was freely mobile. There was no

obvious soft tissue redness or increased temperature. No

other bone or joint pain was noticed, nor stiffness of the

temporo-mandibular joint. He claimed to have no history

of injury.

CT examination was performed on a Lightspeed VCT

64-slice system provided by GE Medical Systems. Non-

contrast scans (0.6 mm) of the entire skull were acquired

in a 2000:350 window. CT showed multiple infra- and

supracentimetric osteochondroma-like lesions with lobu-

lated well-defined borders and parosteal development at

the level of left temporal bone, left ethmoid, calvaria,

zygomatic arches, maxilla and mandible. Those masses

associated cortical bone thickening, without interruption,

and well delineation with compressive effect on soft tis-

sues (Figures 1-3).

The patient underwent surgical treatment of the big-

gest and most painful lesion (left mandibular) with re-

moval of the pseudocapsule and underlying periosteum

excision. Morphopathological result was that of a lobu-

lated, well-defined mass, with disorganized cartilage and

patchy ossification, large chondrocytes and osteoblasts,

without atypias.

Clinical and imaging findings were consistent with

diagnosis of bizarre parosteal osteochondromatous pro-

liferation, certified by morphopathological result.

*Corresponding author.

R. BAZ, C. NISCOVEANU

134

Figure 1. Axial CT-scans showing multiple lobulated well-

defined lesions at the level of mandibular angles (a,b); left

mandibular ramus (c,d); zigomatic arches (e) and ethmoi-

dal bone (f).

Figure 2. Coronal CT reformats showing the same man-

dibular lesions (a, b, c, d) and smaller ones at the level of

calvaria (c,d), with heterogeneous structure and without

continuation with normal cortical bone.

3. Discussion

Bizarre parosteal osteochondromatous proliferation

(Nora’s disease) is a rare benign lesion usually seen in

young adults, although it can appear in any age group. It

Figure 3. Volume rendering images indicating multiple

hard masses in calvaria, maxillar bones and mandible

(a,b,c,d).

affects men and women in equal proportions. Some au-

thors believe the etiology is due to minor trauma but

there is still no imaging or pathologic evidence to support

this. Patients usually present with the history of a slowly

growing mass or pain, as in our patient.

The following specific radiological findings help to

distinguish BPOP from many of its mimickers including

solitary osteochondroma:

1. The tumor appears to arise from the surface of the

cortex directly.

2. There is no continuity between the central part of

the tumor and the medulla of the underlying bone.

3. There is no flaring of the cortex of the underlying

bone [6].

On computed tomography scan, BPOP is typically well

delineated without continuity with the cortex of the me-

dullar canal, like in osteochondromas. The lesion may

exhibit a spiculated or irregular surface leading to a pos-

sible misdiagnosis of malignancy such as osteosarcoma.

In contrast to malignant lesions, BPOP exhibits no perio-

steal reaction and has normal radiological underlying

bone and adjacent soft tissu e.

BPOP has been described as a lesion with a nodular

surface covered by glistening cartilage and a distinct blue

tint of the bone within on gross examination. The pe-

riphery of the lesion contains lobulated hypercellular

cartilage and fibrous tissue with occasional large chon-

drocytes. There are uniform osteoblasts on the bony tra-

beculae. Chondrocytes may be binucleated and prolifera-

R. BAZ, C. NISCOVEANU

135

tion of bizarre (even spindle shaped) fibroblast in the

intertrabecular spaces of disorganized bone has been re-

ported. Typically the cartilage lobules show mild atypia

and moderate mitotic activity is seen in the spindle cells.

This often conf uses the diagnosis and the lesion n eeds to

be distinguished from conventional osteosarcoma, low-

grade parosteal osteosarcoma, and chondrosarcoma. There

is no “columnation” of the cartilage as in osteochon-

droma, rather the cartilage is disorganized and irregular,

with patc hy areas of ossification [7].

The recommended treatment of choice is excising the

pseudocapsule over the lesion, any periosteal tissue be-

neath the lesion, and decorticating any abnormal appear-

ing areas in the underlying host bone, as this procedure

has less recurrence rate than simple excision of th e lesion

[8].

These lesions have a remarkable tendency to recur:

recurrence rates between 29% and 55% in a 2-year in-

terval have been reported, and almost half of those pa-

tients have had a second recurrence. [9] Nora and col-

leagues presented 35 cases of BPOP with 18 (51%) local

recurrences [1]. Meneses and colleagues reported a re-

currence rate of 55% in a series of 65 patients [2] and

Dhondt and colleagues reported a recurrence rate of 29%

in 24 patients [10]. However, despite a high tendency to

recur and a sometimes atypical histological appearance,

no malignant transformation, metastases, deaths or asso-

ciated systemic diseases have been described so far in

patients with BPOP.

4. Conclusion

Nora’s lesion represents a distinct radio-pathological

entity. It should be considered whenever the diagnosis of

osteochondroma is made. Being a rare lesion, the diag-

nosis of Nora’s lesion is challenging for most radiolo-

gists and pathologists as illustrated by this case and oth-

ers. The particularity of our case is the distinct localiza-

tion of the lesions, with very few cases of BPOP of the

skull bein g r ep or t ed.

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