CASE 9652 Published on 27.12.2011

Brown tumors as initial finding in primary hyperparathyroidism

Section

Musculoskeletal system

Case Type

Clinical Cases

Authors

Matos H, Barbosa L, Estevão A

Centro Hospitalar de Coimbra, Portugal
Patient

32 years, female

Categories
Area of Interest Musculoskeletal bone, Musculoskeletal joint ; Imaging Technique CT, Ultrasound
Clinical History
32-year-old female patient, reporting bilateral knee pain. Symptoms evolved over the past two years, with recent aggravation. No known history of trauma was present.
Imaging Findings
Plain radiographs of knees (Fig.1) presented lytic lesions in the patella, with sclerotic borders, slightly expansile.

CT (Fig. 2) confirmed the lesions and their lytic nature, with cortical thinning and bulging of the contour. Attenuation values were in the range of fibrous tissue and blood. No soft tissue mass was present.

One of the diagnoses considered was of brown tumours. This hypothesis was emphasised after performing plain radiograph of hands (Fig. 3), which presented subperiosteal bone resorption in the radial aspect of the middle phalanges (Fig. 3b).

The diagnosis was confirmed with blood workup (high parathyroid hormone levels) and with histological analysis of the lesions.

Afterwards, neck ultrasound demonstrated a hypoechoic mass within the right parathyroid gland (2.5x1 cm). This finding was compatible with parathyroid adenoma (Fig. 4).
Discussion
Brown tumours are well-defined expansile lytic lesions of bone, considered part of a reparative cellular process, rather than a true neoplasm. They are more frequent in primary hyperparathyroidism [1].

Parathyroid glands (PG) secrete parathyroid hormone (PTH), responsible for regulation of serum calcium (SC) concentrations and bone metabolism [2]. In primary hyperparathyroidism, high serum PTH and SC concentrations are related to adenomas or other changes of PG [2]. In secondary hyperparathyroidism, the high levels of PTH are due to resistance to PTH or persistence of hypocalcemia. High PTH levels increase bone turnover, inducing a catabolic state with higher osteoclastic activity, causing demineralization of bone [2]. Subperiosteal bone resorption is an early radiologic finding of hyperparathyroidism, more frequently present in the radial aspect of the middle phalange, distal clavicles and medial aspect of proximal tibia [3].

The increased bone loss in a small area replaces the normal marrow contents by haemorrhage, granulation and fibrous tissue, giving origin to brown tumours [1]. The characteristic brown coloration is a result of haemosiderin deposition [4].

Primary lesions of the patella are a rare finding [5]. Singh J. et al [5] published a multicentre experience with a total of 59 cases, almost half of them representing non-neoplastic conditions, such as brown tumours or osteomyelitis. 39% were due to benign conditions (chondroblastoma and giant cell tumour were the most frequent). Metastatic lesions were the most frequent malignant lesions.
Chondroblastoma occurs more frequently in second decade, typically as a lytic lesion, with lobulated and well-defined sclerotic contours in the epiphysis of immature long bone [5].
Giant cell tumours generally occur in third decade as lytic expansile lesions, larger than chondroblastomas, with cortex thinning [5].
Bilateral lesions appear more frequently due to non-neoplastic conditions (such as brown tumours) or metastatic lesions.
Brown tumours are more frequent in the mandible, ribs, pelvis and clavicle, and uncommon in the patella [1]. Metastatic lesions can be multiple and have a lytic appearance, generally occurring in older patients.

In our case, due to the involvement of both patella and the age of the patient, a non-neoplastic condition was a more probable cause. The first diagnosis considered was in fact brown tumours, which was confirmed by histology and laboratory work up.

The treatment of brown tumours is achieved by resolution of the cause of hyperparathyroidism with normalisation of PTH and SC levels, usually leading to remineralisation and resolution of the lesions.
Differential Diagnosis List
Brown tumours in the patella.
Chondroblastoma
Giant cell tumours
Metastatic disease
Final Diagnosis
Brown tumours in the patella.
Case information
URL: https://www.eurorad.org/case/9652
DOI: 10.1594/EURORAD/CASE.9652
ISSN: 1563-4086