Keywords
chondroma - chondromatosis, synovial - knee - soft tissue neoplasms
Introduction
Soft-tissue chondromas are small well-defined nodular lesions of the cartilage not
attached to bone or the periosteum. They are also known as extraskeletal intramuscular
chondromas (EICs). First described by Baumuller (1883),[1] the incidence of EIC is of ∼ 1.5% of benign soft-tissue tumors.
They occur in the second to seventh decades of life predominantly in the third and
fourth decades.[2] These are slow-growing tumors with a male predominance. The hand and feet are the
most common sites. They present as enlarging painful nodules.[3]
Rare in the lower extremities, the foot is the most common site for the development
of EIC. The thigh, the popliteal region, the knee, and the leg are rare sites.[4] In the present article, we describe a case of EIC in the left knee in a 25-year-old
female patient.
Case Report
A 25-year-old housewife noticed a painless swelling in the inner aspect of the left
knee for 2 years. It was slowly increasing in size. There was no fever, constitutional
symptoms, or trauma. Her activities of daily living were not affected. There was an
oval non-tender swelling (measuring 8 cm × 5 cm × 4 cm) over the anteromedial aspect
of the left-knee joint. There were no features of local inflammation. It had smooth
surfaces, regular borders, well-defined margins, and firm consistency, arising from
the underlying quadriceps muscle. The movements of the knee joint were normal, with
no distal neurovascular deficits or local lymph-node enlargement. Rhabdomyoma, neurofibroma,
intramuscular lipoma, and bursal swelling were considered as our differential diagnoses.
Her hemogram, erythrocyte sedimentation rate (ESR), and levels of C-reactive protein
were normal. The X-ray image of the left-knee joint showed a soft-tissue lesion in
the anteromedial aspect with multiple calcifications ([Fig. 1]). A magnetic resonance imaging (MRI) scan of the left knee showed a large soft-tissue
mass measuring 6.6 cm × 5 cm × 3.7cm arising from the vastus medialis muscle in the
anterior compartment of the left thigh. There were areas with signal intensity similar
to subcutaneous fat and areas of dystrophic calcification within the lesion. The joint
cavity and synovium were unaffected. The adjacent subcutaneous fat and muscle were
normal, without surrounding inflammatory changes ([Fig. 2]). Then, chondroid lipoma, well-differentiated liposarcoma, and malignant fatty tumors
became the differential diagnoses.
Fig. 1 X-ray image of a 25-year-old female patient who presented with slow-growing swelling
of the left knee. The radiograph showed a soft-tissue lesion in the anteromedial aspect,
with multiple punctuate and circular calcification.
Fig. 2 An MRI scan of the patient showing a large soft-tissue mass measuring 6.6 cm × 5 cm × 3.7cm
arising from the vastus medialis muscle in the anterior compartment of the left thigh.
The lesion had areas with signal intensity similar to that of subcutaneous fat with
soft-tissue nodules. There were areas of dystrophic calcification within the lesion.
The joint cavity and synovium were unaffected.
Through a 10-cm long lazy-S incision over the swelling, the skin and subcutaneous
tissues were opened, and excision of the swelling, including a cuff of normal muscle,
was performed. The swelling was arising from the vastus medialis muscle with a pseudocapsule
([Fig. 3]).
Fig. 3 Intraoperative photograph showing a soft-tissue swelling measuring 7 cm × 4 cm × 4 cm
arising from the vastus medialis muscle with a pseudocapsule. There was no infiltration
into the surrounding soft tissue or bone.
Macroscopically, the swelling was a well-circumscribed nodular mass measuring 7 cm × 4 cm × 4 cm
with attached muscles ([Fig. 4]). The cut section was greyish-white and yellowish, with gritty and myxoid areas,
and the muscles were normal. Microscopically, the tumor was composed of nodules of
mature hyaline cartilage with lacunar spaces with chondrocytes. Some chondrocytes
show lace-like calcification. The cartilaginous tissues are separated by loose fibromyxoid
tissue and adipose tissue. Focal areas of ossification were evident. There was no
evidence of cellular atypia, mitosis, or necrosis. The resected margins showed normal
skeletal muscles ([Fig. 5]). The histopathological diagnosis was EIC.
Fig. 4 Photograph of the resected specimen.
Fig. 5 Microscopy of the resected specimen showing nodules of mature hyaline cartilage with
lacunar spaces with chondrocytes. Some chondrocytes show lace-like calcification.
The cartilaginous tissues are separated by loose fibromyxoid tissue and adipose tissue.
Focal areas of ossification were evident. There was no evidence of cellular atypia,
mitosis, or necrosis. The resected margins showed normal skeletal muscles.
The postoperative period was uneventful. The sutures were removed on the tenth day.
The patient was asymptomatic thereafter. No recurrence was observed after three years
of follow up. We obtained consent to publish the present report.
Discussion
Extremely rare soft-tissue tumors, EICs arise without direct attachment to bone or
the synovium. There is controversy regarding their origin. Some authors consider that
they originate from the synovium, while other authors[3] consider them a developmental fault or metaplasia. Malignant transformation is rarely
reported. There are reports of male and female predominance, and EICs are observed
near the tendons and tendon sheaths.[3]
Radiographically, calcification is evident in 33% to 77% of the cases. The usual patterns
of calcification include curvilinear, punctuate, and mixed curvilinear and punctuate
types. Magnetic resonance imaging scans show uniform hypointensity in T1- and T2-weighted
images of homogenous or dystrophic calcification. The radiographic differential diagnoses
are synovial chondromatosis, mesenchymoma, loose bodies, periosteal chondroma, myositis
ossificans, crystal-deposition diseases, synovial sarcoma, and malignant soft-tissue
chondrosarcoma.[5] Histopathologically, they are highly-cellular tumors with mild to moderate nuclear
pleomorphism and scattered mitosis. Areas of focal fibrosis, ossification, and myxomatous
changes are observed. Osteoclast-like giant cells and epithelioid cells with granuloma-like
proliferation are rarely reported.[6] Supernumerary ring chromosomes of varying sizes and numbers were reported in a case
of a soft-tissue chondroma.[7]
These lesions are common in the hands and feet. Soft-tissue chondromas have been reported
in the masseter muscle, tongue, pharynx, larynx, and other parts of the head and neck
region.[8] Extraskeletal intramuscular chondroma can cause trigger finger, symptoms similar
to plantar fasciitis, and Hoffa disease.[9] There was another report[10] of posterior interosseous nerve palsy due to compression by a soft-tissue chondroma.
The excision of the lesion is curative. Recurrence is rarely reported.[9]
Our case was that of a 25-year-old female patient with swelling in the anteromedial
aspect of the left knee. Clinically, we considered such possibilities as rhabdomyoma,
fibroma, neurofibroma, and a bursa. The lesion was within the quadriceps muscle, and
the movement of the knee was restricted when contracting the muscle. Its indolent
course and lack of many symptoms prompted us to consider the diagnosis of rhabdomyoma
or an intramuscular lipoma. Due to the presence of fatty tissue and calcifications
on the MRI scan, the radiological diagnosis was benign lipomatous tumor. But, to our
surprise, the microscopic diagnosis was extraskeletal soft-tissue chondroma. This
case is herein presented to highlight the rarity of this condition and to describe
the clinical and investigative challenges regarding the diagnosis.
Extraskeletal intramuscular chondroma is a rare entity that can clinically mimic other
benign soft-tissue tumors. Histopathology exams can provide a definitive diagnosis.
The excision of the tumor is curative.
