Brown tumour and its differential diagnosis: Challenges in radiological evaluation

A 35-year-old female patient presented with shortness of breath since one year and chest pain radiating to the right shoulder since three months. There was no history of trauma, fever, hypertension or diabetes mellitus.

Chest radiograph

Pleural-based triangular opacity in the right mid & lower zone.

Well-defined expansile lytic lesions with a narrow zone of transition and no matrix calcification in left 5^th rib and right clavicle.

Contrast-enhanced CT Thorax

Well-defined lobulated heterogeneously hypodense expansile lytic lesion in right 6^th rib and extending into extra-pleural space causing cortical thinning and showing heterogeneous post-contrast enhancement with non-enhancing central areas. The lesion has a narrow zone of transition with no periosteal reaction.

Well-defined expansile lytic lesions involving multiple ribs, D9 vertebra, right clavicle and left scapula.

Well-defined heterogeneously enhancing mixed solid-cystic lesion noted posterolateral to left thyroid lobe.

Sections of upper abdomen showed left renal calculi.

AP Radiograph both hands

Diffuse osteopenia.

A well-defined lytic expansile lesion involving the right third metacarpal without any matrix calcification, soft tissue component or transarticular extension is observed.

Subperiosteal resorption on radial aspect of proximal phalanx of middle and ring fingers on right side.

Acro-osteolysis is seen.

Skull Radiograph

Multiple tiny round lucent lesions diffusely involving the cranial vault.

Ultrasound of Neck

A well-defined heterogeneously hypo-echoic, hypervascular lesion in left parathyroid gland.

Various differentials exist for multiple lytic rib lesions including benign entities like fibrous dysplasia, enchondromas, and brown tumour and malignant ones like metastases, multiple myeloma & lymphoma. Radiographic findings, age group, clinical presentation & ancillary features aid in diagnosis.

Malignant lesions are more common in older age groups of patients and present with chest pain in contrast to benign lesions that arise in younger age groups and are asymptomatic in the absence of pathological fractures [1,2,3].

Brown tumour is a rare slow-growing benign lesion in skeletal system that most commonly occurs in mandible, pelvis, ribs and femur due to either primary or secondary hyperparathyroidism [4,5,6]. They are usually diagnosed incidentally on radiographs or CT for other indications. The intensity of bone pain from brown tumour is comparatively milder than radiological findings and malignant bone lesions [4,5,6]. The imaging findings of brown tumour depend on the stage of the lesion and its location. In early stages, it appears as a well-defined radiolucent area with thinning and perforation of the cortical bone. As it grows, it can cause bony expansion and destruction of the normal architecture, leading to bone deformity and erosion. The lesion may appear as a mixed radiolucent-radiopaque mass, with variable density and irregular borders [4].

Imaging can also provide information on its relationship to adjacent structures and the involvement of surrounding soft tissues. Definitive diagnosis can only be made through pathological evaluation which depicts multinucleated giant cells, fibrous stroma, and areas of haemorrhage and hemosiderin deposition.

The incidence of Brown tumour is lower in secondary hyperparathyroidism due to chronic renal failure and vertebral changes like rugger-jersey spine may be seen in such cases [1].

In our case, a lesion in left parathyroid gland, elevated serum calcium levels, and multiple lytic lesions in ribs, clavicle and metacarpal with histopathological evidence of (H&E stained image) showed multinucleated osteoclastic giant cells on haemorrhagic background and Giemsa stained smear showing osteoclastic giant cells.