Cytological Diagnosis of Chondromyxoid Fibroma.

CASE HISTORY

A 19-year-old young male of average built presented to the outpatient department with complaints of swelling over the left ankle for the past 3 years, associated with an increase in size of the swelling in the last 1 year. There was no significant past medical history or any history of trauma. Clinical diagnosis was giant cell tumor of bone.

Magnetic resonance imaging (MRI) showed well-defined cortical-based lesion measuring 5.4 × 3.7 cm, which was hypointense on T1 and hyperintense on T2/Stir sequences seen in distal tibial metaphysis involving the lateral cortex with a narrow zone of transition. Contrast study showed heterogenous enhancement. Overlying cortex was thinned out with breach at some places [Figure 1]. FNAC was done and smears were prepared. Wet fixed smears were stained with hematoxylin and eosin (H&E), and air-dried smears were stained with Wright's stain.

Figure 1

T2-hypointense spindle-shaped mass involving metaphysis of tibia

On cytological examination, the stained smears were cellular with abundant chondromyxoid background. The cells were of variable sizes and shapes; some of them were round to ovoid cells having moderate amount of cytoplasm, benign-appearing nuclei, and bland chromatin. Stellate and spindle-shaped cells were seen singly and in aggregates, along with osteoclastic giant cells [Figure 2a, b]. The overall cytological picture correlating with clinical and radiological details favored the diagnosis of CMF.

Figure 2

(a) Smear showing spindle-shaped cells with osteoclastic giant cells (H&E, 10×). (b) Smear showing spindle-shaped cells embedded in a myxoid matrix (H&E, 40×). (c) Section showing myxochondroid appearance along with fibrocollagenous tissue and osteoclastic giant cells (H&E, 10×) H&E = hematoxylin and eosin

A preoperative diagnosis of CMF helped to give treatment as curettage combined with bone grafting. The sample was collected and sections were prepared for histopathologic examination.

Section studied showed hypocellular lobules of myxochondroid appearance separated by cellular tissue composed of spindle cells arranged in interlacing bundles; the cells had basophilic spindled nuclei and moderate amount of cytoplasm. Background showed fibrocollagenous tissue and osteoclastic giant cells [Figure 2c]. No mitoses, necrosis, or calcifications were seen. The findings were consistent with the diagnosis of CMF.

DISCUSSION

CMF is a very rare benign chondroid neoplasm. It is usually an intramedullary eccentric lesion located in the metaphyseal region of the long bones surrounding the knee, but it can also be seen with relative frequency in other long bones, pelvis, ribs, and small foot bones.[1] It usually presents in patients during their second and third decades and has a slightly higher incidence in males. Patients usually complain of a slow-growing, painful swelling.

The tumor is considered as a physeal plate remnant and may involve the epiphysis, diaphysis, or both along with its metaphyseal origin. It may cause cortical expansion and destruction, but consistently respects the periosteal boundary. CMF is one such tumor that is characterized by incomplete cartilage differentiation.[1] The helpful features are the peripheral intermediate signal band and central hyperintense signal on T2-weig hted images, generally corresponding to the peripheral nodular enhancement, and a central non-enhancing portion on contrast-enhanced T1-weighted images.[2]

Walke et al.[3] reported two cases of CMF of lower end of femur and upper end of tibia, and Siddiqui et al.[4] reported a similar case in fourth metatarsal head of an 18-year-old boy. Both studies revealed background showing chondroid and myxoid elements. The cellular elements comprised spindle cells, stellate cells, chondroblasts, and few osteoclastic giant cells. Diagnosis in all the above cases was confirmed on histopathologic examination after resection of the tumor.

Bergman et al.[5] reported four cases of CMF in the metaphyseal region of tibia, fibula, humerus, and ischium. The cytological finding and usefulness of fine needle aspiration biopsy in the diagnosis of CMF are emphasized.

Our case had similar cytological findings, but chondroblastoma had to be ruled out.

Chondroblastoma is characteristically a well-defined, epiphyseal lesion with sclerotic rim and matrix calcification, but CMF is a metaphyseal lesion.[3] On cytological examination, chondroblastoma contains a more uniform population of monon uclear cells (chondroblasts) with round to ovoid nuclei and nuclear grooves compared with a more polymorphous population of stellate, ovoid, and spindle cells found in CMF. Chondromyxoid matrix is also more commonly found in CMF compared with cell-rich chondroblastoma. Nevertheless, there can be considerable overlapping of cytomorphologic features, which may make it difficult to distinguish between these two entities. CMF can also be mistaken for chondrosarcoma on cytology, especially the myxoid variant, due to the presence of chondroid and myxoid matrix in the background. Chondrosarcoma characteristically shows fragments of hyaline cartilage and cells sitting in the lacuna. The individual cells can be uninucleate or binucleate, showing nuclear pleomorphism and frequent mitosis [Table 1].[3]

Table 1

Differential diagnosis

Tumor type	Chondroblastoma	Enchondroma	CMF	Chondrosarcoma
Clinical features	Young patient, long bones	Young patient, appendicular skeleton	Second and third decades, long bones	Third to sixth decade of life, axial skeleton
Radiology	Well-defined lucent epiphyseal lesion with sclerotic rim showing geographic bone destruction	Intramedullary meta-diaphyseal solid lesion with size <5 cm, no periosteal reaction and endosteal scalloping	Well-demarcated, osteolytic metaphyseal lesion with expansion of the cortex	Ill-defined, larger lytic metaphyseal lesion with geographic destruction with periosteal reaction and endosteal scalloping
FNAC	Uniform population of mononuclear cells (chondroblasts) with round to ovoid nuclei and nuclear grooves, multinucleated osteoclast-like cells, and fragments of chondroid material	Cells in lacunar space having uniform, rounded nuclei, well-defined cytoplasm, and abundant chondromyxoid ground substance	Polymorphous population of stellate, ovoid, and spindle cells, osteoclast-like giant cells embedded in chondromyxoid matrix	Cells have rounded nuclei with one or two nucleoli, well-defined cytoplasm, binucleate cells with moderate degree of nuclear pleomorphism and abundant chondromyxoid ground substance
Histopathology	Sheets of ovoid to polygonal cells with small, grooved nuclei and distinct cell borders. Interspersed osteoclast-like giant cells and islands of chondroid matrix with pericellular lace-like or chicken wire calcification is characteristic	Hypocellular with lobules of mature hyaline cartilage, which are encased by surrounding normal bone. Foci of myxoid degeneration, calcification, and endochondral ossification are common	Hypocellular lobules with a myxochondroid appearance, separated by intersecting bands of highly cellular tissue composed of fibroblast-like spindle cells and osteoclasts. Calcification may occur	Abundance of cartilaginous matrix, hyalin, and sometimes myxoid changes. Hypercellular lobules, cells having small, condensed nuclei and separated by fibrous bands with entrapment of pre-existing lamellar bone trabeculae

CMF=chondromyxoid fibroma, FNAC=fine needle aspiration cytology

The histopathologic picture of CMF is characteristic with lobular arrangement of myxoid and chondroid tissue surrounded by zones of hypercellular fibrous tissue.

A preoperative diagnosis of CMF was very important, so as to avoid radical surgical procedures. The ideal treatment is curettage combined with bone grafting.

Immunohistochemical analysis is generally not useful in distinguishing CMF from other entities; however, recent studies have demonstrated that the chromosomal abnormality [inv (6) (p25q13) pericentromeric inversion] is a useful marker for CMF.[6]

Although CMF is an unusual bone tumor, the cytological features are distinctive enough to make a diagnosis after clinico-radiological correlation.

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Conflicts of interest

There are no conflicts of interest.