Keywords costochondral junction - giant osteochondroma - ribs - solitary exostosis
Introduction
Benign tumors commonly encountered in the ribs are fibrous dysplasia and enchondroma.[1 ] Osteochondromas arise from the metaphysis and constitute 20 to 50% of all benign
bone tumors and 10 to 15% of all bone tumors. These commonly develop during the first
decade of life but stop growing when the individual reaches skeletal maturity. Males
are affected 1.5 times more commonly than females.[2 ] The tumor commonly occurs in long bones but rarely affects ribs with an incidence
of 2 to 8%.[3 ] The rib tumors are usually small, and occurrence of a giant costal osteochondroma
is rare in adults.[4 ]
[5 ]
[6 ]
This case is unique for large size, longstanding at an unusual location, yet lack
of malignant transformation. We encountered no such gigantic osteochondroma of rib
which possessed a diagnostic challenge due to undetectable cartilage cap which was
completely ossified.
Case History
A 38-year-old woman presented with a 15-year history of swelling on left side of chest
wall which had gradually progressed to the present size of 16 × 16 cm. Initially,
she noted swelling of 2 × 2 cm in size which progressed to present size measuring
16 × 16 cm causing disfigurement. Some area of skin ulceration was noted along with
a discharging sinus over the swelling. According to the patient, one biopsy was attempted
2 years back which triggered the spurt in growth of swelling. There was no history
of trauma to ribs, tuberculosis, hypertension, or diabetes or any surgery in the past.
This swelling was not painful, so she was not taking any medication for pain. There
was no history of blood discharge from the wound of ulceration. On palpation, it was
bony hard and skin was stretched over it but intact.
Chest radiographs (anteroposterior and lateral views) showed a dense, round, well-defined
bony outgrowth overlying almost whole of left chest wall showing large extrathoracic
component. Lucency over surface corresponded to ulceration and sinus formation. The
breast shadow was seen separately ([Fig. 1A, B ]).
Fig. 1 (A ) Chest X-ray, anteroposterior view, showed a large, well-defined, round bony tumor
over left chest wall, over and below left clavicle reaching till diaphragm displacing
left breast inferolaterally. (B ) On lateral radiograph, the mass is seen over the sternum suggestive of extrathoracic
component.
Noncontrast computed tomography (CT) scan showed a mushroom-shaped mixed signal density
mass showing bony and fluid components mixed with fat density arising from costochondral
junction of left second rib. Both intrathoracic and extrathoracic components were
of almost similar size. The tumor demonstrated continuity with periosteum at costochondral
junction of left second rib with extension into pleural cavity. Cortical and medullary
continuity between the tumor and parent bone was noted ([Fig. 2A–E ]). The growth was causing collapse of ipsilateral lung (lingular lobe) and abutting
pericardium but with clear fat planes ([Fig. 2F, G ]). Periosteum was intact and there was no evidence of soft tissue infiltration. The
mass showed little or no enhancement on contrast CT ([Fig. 2H–K ]).
Fig. 2 (A ) NCCT of the thorax: Large bony tumor with cystic spaces abutting arch of aorta,
origin seen from left second rib. (B ) NCCT of the thorax: Dumbbell-shaped tumor with surface sinus. (C ) CT of the thorax: Tumor is seen in left hemithorax abutting main pulmonary trunk
and left pulmonary artery. (D ) NCCT of the thorax: Tumor is abutting pericardium and compressing left lingular
lobe bronchus. (E ) NCCT of the thorax: Lower extent of the tumor, left breast seen separately. (F ) CT of the thorax (lung window): Normal right lung field, consolidation of the left
lung adjoining the tumor. (G ) CT of the thorax (lung window): Normal right lung field, consolidation of the left
lung adjoining the tumor. (H ) CECT image shows tumor contents (bony, fluid, and some fat densities) and relationship
with arch of aorta. (I ) CECT of the thorax: Left subclavian artery in close opposition to medial tumor margin.
(J ) CECT of the thorax: Close contact of the tumor with pericardium. (K ) CECT of the thorax: Lower extent of tumor, clear margin seen with mediastinal structures.
CECT, contrast-enhanced computed tomography; CT, computed tomography; NCCT, noncontrast
computed tomography.
On magnetic resonance imaging, the mass was of mixed signal intensity on T1- and T2-weighted
images with predominantly bony contents with cysts formation. There was a sinus (measuring
6 × 2.7 cm) showing fluid–fluid level. Postcontrast scans revealed minimal or no enhancement
in most of tumor parts ([Fig. 3A–G ]).
Fig. 3 (A ) MRI: 3D T2 space stir tra showing heterogeneous tumor contents at arch level, clear
fat planes. (B ) MRI: 3D T2 space stir tra, tumor at pulmonary trunk, compressing left pulmonary
artery. (C ) MRI: T2 tirm tra. Mixed intensity tumor contents showing extrathoracic and intrathoracic
extension. (D ) MRI: T2 tirm tra. Mixed intensity tumor contents showing extrathoracic and intrathoracic
extension. (E ) MRI: T2 haste tra. Tumor showing clear fat planes with aortic arch. (F ) MRI: T2 haste tra. Tumor closely abutting left subclavian artery, caution for surgeon.
(G ) MRI: 3D T2 space stir cor. Intrathoracic and extrathoracic tumors showing relations
with mediastinal structures and breast. MRI, magnetic resonance imaging.
Positron emission tomography (PET) scan revealed low-grade heterogeneous fluorodeoxyglucose
(FDG) uptake in the tumor. Low-grade FDG uptake was seen in deeper aspect of calcified
mass adjacent to anterior part of left second rib (maximum standard unit value [SUVmax ] 1.3). Increased FDG uptake was also noted in the tissue surrounding the ulceration
(SUVmax 2.9). Rest of the masses did not show any significant SUV uptake. Normal metabolic
activity was seen in the myocardium. Lungs showed no hypermetabolic pulmonary nodules.
There was no active mediastinal, axillary, and hilar lymphadenopathies ([Fig. 4A, B ]).
Fig. 4 (A, B ) PET image: Increase FDG uptake at sinus site due to active inflammation. No uptake
was noted in main tumor suggesting benign etiology. FDG, fluorodeoxyglucose; PET,
positron emission tomography.
All radiologic findings and PET were suggestive of benign primary bony tumor. Diagnosis
of osteochondroma was kept after ruling out possibilities of giant cell tumor, atypical
fibrous dysplasia, and chondrosarcoma. Considering the large size leading to disfigurement,
sinus discharge, compression of left lung causing breathlessness surgery was planned.
Mediastinal sternotomy and “trap-door” thoracotomy were performed with removal of
tumor mass into two pieces, along with removal of second and third ribs. Intraoperatively,
it was a hard bony dumbbell-shaped mass, 5.5 kg in weight arising from left second
rib and was decorticating third rib. Adjoining left lung was collapsed. Chest wall
reconstruction was done with pectoralis major muscle flap.
Postoperative period was uneventful and the postoperative chest X-ray showed air entry
into collapsed left lung ([Fig. 5 ]). On 3 years follow-up, patient was doing fine.
Fig. 5 Postoperative chest X-ray shows good expansion of left lung.
Gross specimen examination revealed round hard bony mass of uniform contour with extrathoracic
component of 16 × 16 cm and intrathoracic component measuring 22 × 17 cm ([Fig. 6 ]). Cut section revealed tumor as a mess of bony trabeculae and cavities filled with
blood.
Fig. 6 Gross specimen cut into two pieces (was not possible to remove in whole due to huge
size).
Histopathology from intrathoracic component revealed a homogenous picture showing
interlacing mature bony trabeculae with intervening hematopoietic to fatty marrow.
Sections from hemorrhagic and myxoid areas of extrathoracic tumor showed woven bone,
fibrocellular stroma, congested capillary channels, and large areas of hyalinization.
Rest of the tumors showed mature bony trabeculae with intervening hematopoietic to
fatty marrow. No cartilaginous cap was identified in both components on extensive
sampling ([Fig. 7A–D ]).
Fig. 7 (A ) Histopathology: Bony trabeculae in fatty marrow. (B ) HPE: Bony trabeculae in hematopoietic marrow. (C ) HPE: Foci of hyalinization and calcification. (D ) HPE: Fascicles of spindle cells in marrow spaces.
Based on clinicoradiopathologic correlation, a diagnosis of osteochondroma was rendered.
Discussion
Osteochondromas can be solitary or multiple, multiple lesions are usually seen in
association with hereditary multiple exostosis (HME). They may present as a pedunculated
or sessile mass protruding from the parent bone. The characteristic radiologic findings
are of a lesion composed of cortical and medullary bone with an overlying hyaline
cartilage cap. It is a developmental lesion arising when the endochondral bone growth
is most active. The ring of Ranvier covering the epiphyseal growth plate is defective,
and it is thought that due to cut back remodeling, a fragment of epiphyseal growth
plate cartilage protrudes laterally through this defect, instead of its usual descent
to metaphysis. Eventually, there is endochondral ossification of this lateral extension
which is seen as a cartilage cap covered protrusion on the bony surface. Its cortex
is in direct continuity with the cortex of the affected bone, being enveloped by its
periosteum. For a diagnosis of osteochondroma to be made, this bony outgrowth must
have a direct continuity with the underlying cortex and medullary canal.[2 ]
The cartilaginous cap has varied morphology, radiologically presenting as either a
smooth and uniform contour or as an irregular and bosselated surface with a cauliflower-like
appearance. The thickness of this cap changes with increasing age, it may be several
centimeters thick in children and adolescents, whereas it may be only a few millimeters
in an adult or may be completely absent in some cases. This absence is usually a result
of wear and tear abrasion, although it has also been recognized that rarely osteochondromas
may lose the cartilaginous cap in very longstanding lesions. The cartilaginous cap
in the present case was not discernible even after extensive sectioning. At an advanced
age, the cartilaginous cap may become fully ossified so that only an “osseous exostosis”
remains without any cartilage.[2 ]
[7 ]
Complete radiological skeletal survey should be performed in cases with multiple osteochondromas
to work up for any other significant anomaly and to rule out HME.[2 ]
In the present case, various differential diagnosis were considered on the basis of
histology in the form of hematopoietic pseudotumor, posttraumatic fibro-osseous lesion
of ribs, and variant fibrous dysplasia. The diagnosis of hematopoietic pseudotumor
was considered in view of abundant hematopoietic marrow and absence of cartilaginous
cap. However, this was ruled out based on lack of hematologic abnormalities and unusually
large size of lesion. Posttraumatic fibro-osseous lesion of ribs and variant fibrous
dysplasia were also ruled out based on lack of classic radiologic findings and presence
of abundant hematopoietic marrow, although small foci of woven bone formation, fibrous
stroma, and hyalinization were noted.
The diagnosis was strongly supported by the radiologic picture of mushroom-shaped
growth arising from anterior region at costochondral junction. Cortical and medullary
continuity between osteochondroma and parent bone was characteristic of osteochondroma.[2 ]
The only other giant costal chondrosarcoma reported by Liu et al was associated with
malignant transformation and HME unlike our case.[8 ] Alhames and Almhanna have also reported a case of large osteochondroma without any
associated family history, but the size is smaller than the present case.[9 ]
[10 ] The spectrum of complications which may be seen ranges from deformity, fracture,
vascular compromise, neurologic sequelae, overlying bursa formation to malignant transformation
in some cases; however, they are more frequent in cases with underlying multiple hereditary
exostosis. Malignant transformation is assessed by the presence of a thick cartilage
cap more than 1.5 cm even after attainment of skeletal maturity and a progressive
increase in the growth. It is an uncommon occurrence and can be seen in 1% of solitary
osteochondromas and in 3 to 5% of patients with HME.[2 ] There was no evidence of malignant transformation in this case on extensive sampling.
Conclusion
This case is rare for the large size, unusual location, and yet lack of malignant
transformation. Costal osteochondroma is an important condition to recognize due to
its complications such as reduced range of movement, pain, cosmetic abnormalities,
and bursitis. These may grow into the chest cavity and cause compressive symptoms.
The importance of clinicoradiologic correlation and loss of cartilaginous cap in longstanding
cases of osteochondroma is exemplified.[2 ]
[7 ]
