Orthopaedic Case of the Month: Painful Lower-leg Mass in a 76-year-old Man

History and Physical Examination

A 76-year-old man was referred for evaluation of a right lower leg mass. He reported an acute exacerbation of chronic pain in the affected limb. He had no recent injury or antecedent trauma but recalled a remote history of a right tibia fracture 60 years previously that was treated nonoperatively, with subsequent mild chronic leg pain attributable to the fracture. He stated that he had always perceived a ‘knot’ over the area since the injury, but that the knot had progressively enlarged during the last 3 months. His symptoms were activity-related but he also complained of weakness in the leg that had been present since the initial injury. He denied fevers, chills, night pain, or weight loss.

The patient presented to an emergency room 3 weeks before evaluation, where a duplex ultrasound and bone scan were obtained for suspected deep vein thrombosis and workup of the leg mass. The ultrasound was negative for blood clots. Bone scan revealed increased uptake in the affected leg during the soft-tissue and bone phase. He was given a prescription for an NSAID and told to continue weightbearing as tolerated. He was referred for further evaluation and treatment.

His medical history was significant for Parkinson’s disease, hypercholesterolemia, depression, and benign prostatic hypertrophy.

His physical examination revealed a diffuse soft tissue mass that was tender to palpation (Fig. 1). The mass was 9 cm × 6 cm and relatively firm with some areas of fluctuance; there was no surrounding erythema or warmth. He had mild weakness (4/5) of the tibialis anterior and extensor hallucis longus but no other neurologic deficits. His vascular examination was normal.

Fig. 1.

The 9 × 6 cm bulky mass can be seen over the anterolateral aspect of right lower leg.

Laboratory analysis including complete blood count, serum chemistry panel, and anticoagulation panel, were within normal limits. Radiographs of the right leg were obtained on initial evaluation (Fig. 2).

Fig. 2A–B.

(A) AP and (B) lateral views show a large oval-shaped area of dense mineralization with central lucency seen best in the lateral projection. This mass was superimposed on the fibula in the frontal projection and anterior tibia on the lateral view and thus believed to be soft tissue in origin. There is no cortical erosion or underlying periosteal reaction.

Based on the history, physical examination, laboratory studies, and imaging studies, what is the differential diagnosis?

Imaging Interpretation

AP (Fig. 2A) and lateral (Fig. 2B) radiographs of the right leg revealed a soft tissue lesion with disorganized mineralization located in the anterior compartment. There was no cortical erosion or periosteal reaction in the underlying tibia. MRI confirmed the presence of a large well-circumscribed soft tissue mass in the anterior compartment of the leg that aligned with the muscle fibers. T1-weighted sagittal and axial MR images showed a mass with heterogeneous signal intensity that was isointense with muscle, whereas T2-weighted sequences produced a heterogeneous hyperintense signal (Figs. 3–4).

Fig. 3A–B.

(A) T1-weighted sagittal and (B) axial fast spin echo images show a well-circumscribed lesion with a low intensity peripheral rim and central signal intensity that is isointense to hyperintense to muscle. The central high signal on the T1-weighted image is suspicious for proteinaceous material or blood products. The globular areas of low signal most likely represented more focal or “chunky” areas of calcification.

Fig. 4.

A T2-weighted axial fat-suppressed image shows a heterogeneous hyperintense signal.

Differential Diagnosis

Malignant tumors with a propensity to mineralize, eg, synovial sarcoma, soft tissue osteosarcoma, soft tissue chondrosarcoma

• Tumoral calcinosis

• Myositis ossificans

• Calcific myonecrosis

• Dermatomyositis/polymyositis

A TEMNO^® (Cardinal Health, Dublin, Ohio, USA) needle biopsy was performed in addition to needle aspiration. Specimens were sent for histopathologic analysis, Gram stain, and culture.

Based on the history, physical examination, laboratory studies, imaging studies, and photomicrographs, what is the most likely diagnosis and how should the patient be treated?

Histologic Interpretation

Needle aspirates showed a yellow, chalky material. The Gram stain and culture results showed no organisms, leukocytes, or bacterial growth. A core needle biopsy showed rare macrophages, scant cellular debris, and amorphous mineral deposition. Additional tissue samples were obtained during the subsequent surgical resection of the mass and were evaluated microscopically (Fig. 5).

Fig. 5.

A photomicrograph of tissue obtained from the soft tissue mass shows rare macrophages and amorphous mineralized material (Stain, Papanicolaou; original magnification, ×400).

Diagnosis

Calcific myonecrosis of the anterior compartment of the right leg.

Discussion and Treatment

Calcific myonecrosis was diagnosed based on the history of a remote antecedent leg injury with a resultant slow growing soft tissue mass, combined with characteristic radiographic findings and normal laboratory values. Plain radiographs show soft tissue calcification conforming to muscle shape. Occasionally, adjacent bony erosions with smooth contour can be present. MRI will show heterogeneous intensity on T1- and T2-weighted images owing to subacute hemorrhage and proteinaceous contents without enhancement after gadolinium administration [5].

Some soft tissue sarcomas, especially synovial sarcoma, soft tissue osteosarcoma, and chondrosarcoma, might mineralize and must be considered in the differential diagnosis [14, 21, 33]. A synovial sarcoma is a malignant lesion primarily composed of epthelioid and spindled cells. Radiographically, 30% or these tumors may mineralize. MRI shows a heterogeneous mass with predominately high signal intensity on T2-weighted images. This signal variability is the result of solid, cystic, and fibrous tumor components. Typically, synovial sarcomas enhance with gadolinium whereas calcific myonecrosis does not [21, 33]. Osteosarcoma is another malignant neoplasm that should be considered in the differential diagnosis. An osteosarcoma may arise in soft tissue (extraskeletal osteosarcoma) and should be distinguished from those that arise on the cortical surface of bone and extend into the surrounding soft tissue (juxtacortical osteosarcoma). Both variants can mimic calcific myonecrosis. Although biopsy may be necessary to confirm the diagnosis, imaging studies and clinical history provide useful information. Extensive bone involvement, the presence of a “pasted-on” appearance or focal medullary bone invasion is not typical of calcific myonecrosis [29]. Tumoral calcinosis occurs as a result of abnormal phosphate metabolism and typically involves large joints. Radiographically, it appears as a well-circumscribed, periarticular, multilobulated, rounded mass. MR studies reveal a heterogeneous lesion with low signal intensity on T1-weighted sequences and high signal intensity on corresponding T2-weighted images. Serum chemistry levels and a periarticular location also may aid in distinguishing tumoral calcinosis from other mineralized lesions [22]. Myositis ossificans is a benign reactive condition whereby muscle focally differentiates into bone after trauma. Radiographically, myositis ossificans matures peripherally and with time has the appearance of mature bone in the soft tissue. On MR images, the early changes are diffuse whereas later the lesion becomes well circumscribed. In these patients, the clinical history of recent trauma, maturation (zonation) pattern, absence of an expanding mass, and a self-limiting clinical course distinguish this lesion from calcific myonecrosis [4, 25]. Dermatomyositis, polymyositis, and other connective tissue disorders frequently involve deposition of calcium in subcutaneous tissue, fascia, and muscle creating lesions that mimic calcific myonecrosis. Superficial lesions can ulcerate through the skin and drain calcium salts. In addition, dermatomyositis primarily involves the shoulder, hip, thigh, and calf. Widespread involvement, characteristic systemic manifestations of the underlying disorder, and lack of antecedent trauma differentiate these lesions from others [2].

Calcific myonecrosis, initially described by Gallie and Thomson in 1960, is a rare, slow-growing mass arising after remote trauma to the affected limb [9]. The primary etiology seems to be an ischemic injury or undiagnosed compartment syndrome [9, 16, 21]. There have been 46 cases of calcific myonecrosis reported in the English literature including the current case. The mean age of patients at presentation is 53 years (range, 34–87 years), and the mean interval between injury and diagnosis is 37 years (range, 5–64 years) [1–3, 5–21, 23, 24, 26–28, 30–33]. The lower limbs are involved in most cases although there is a report of upper extremity involvement [15]. The anterolateral compartment of the lower leg is the area most commonly affected [1]. The lesion consists of peripheral calcification and central liquefaction. The clinical history may involve associated symptoms of pain and discomfort. Laboratory studies including complete chemistry profiles show normal levels of calcium, phosphate, and alkaline phosphatase. The mass may stay unchanged for many years but also can expand owing to recurrent intralesional hemorrhage which can be symptomatic.

Radiographic features are a well-defined, calcified fusiform mass. Calcifications are plaque-like or sheet-like and are organized around the periphery of the lesion. Pressure erosions can occur over the surface of adjacent bone and typically are smooth and focal [13, 16, 21, 27, 33]. Extensive erosions or periosteal reaction should prompt the investigator to order MR studies to differentiate the lesion from a sarcoma. T1- and T2-weighted sequences show heterogeneous intermediate signal and high signal, respectively, and central fluid regions [13]. The margins show low signal intensity signifying calcification and fibrosis. The lesion does not enhance with contrast administration [21, 27, 33]. Histology sections have cystic areas composed of necrotic muscle and debris containing cholesterol, fibrin, and calcific deposits [17, 18, 21, 32]. Repeated intralesional hemorrhage causes the mass to enlarge and calcify [21, 33]. Later enlargement leads to herniation through the muscle fascia.

Treatment should be guided by clinical symptoms. It generally is thought that less invasive procedures are associated with better patient satisfaction and less complications [13, 14, 31, 33]. Biopsy should be considered only if the diagnosis cannot be made by history and review of imaging studies. Surgery generally is not recommended owing to complications such as blood loss, chronic draining fistulae, secondary infection, and resultant transtibial amputations [11, 13, 16, 21, 31]. Therefore, in the rare cases where symptoms prompt surgery, the considerable risks and benefits always should be reviewed carefully with the patient.

Our patient had a history of remote trauma to his right lower extremity 60 years ago with imaging features that are consistent with the diagnosis of calcific myonecrosis. Given the patient’s diagnosis and symptoms of persistent and increasing pain in the setting of a large expanding lesion at risk for skin ulceration, surgery was recommended. After detailed review of the risks and benefits of surgery, the patient elected to undergo marginal resection and in the intervening year of followup care, there have been no complications and his motor strength remained unchanged. Clinical history, regional growth pattern and location, and characteristic imaging findings can allow the clinician to make the diagnosis of calcific myonecrosis with a fair amount of certainty and might obviate the need for a biopsy altogether in differentiating this disease from other mineralizing soft tissue masses. Failure to recognize calcific myonecrosis can lead to inappropriate management and unnecessary complications.