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.
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).
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.
Brown tumours in the patella.
Based on the provided knee joint X-ray and CT images, localized osteolytic lesions are observed in both patellae, displaying an expansile appearance. The lesion margins are relatively well-defined, with thinning of the bone cortex in some areas but remaining intact. No significant soft tissue swelling or calcifications are noted. On the X-rays of both hands, subperiosteal bone resorption signs can be identified, particularly along the radial side of the phalanges, presenting as thinning or resorption of the cortex. Ultrasound imaging suggests an abnormal parathyroid gland (indicated by the schematic image), potentially indicative of an adenoma or hyperplasia.
Overall, the bilateral lesions exhibit similar morphology and well-defined boundaries, suggesting a higher likelihood of non-neoplastic or benign lesions. Given the context of elevated parathyroid hormone (PTH) and high serum calcium (SC) levels, these findings are consistent with bone changes caused by hyperparathyroidism.
In primary or secondary hyperparathyroidism, bone loss and fibrous tissue proliferation can lead to the formation of brown tumors. Typical imaging features include osteolytic, expansile lesions with well-defined borders, and cortical thinning that remains intact. Persistently elevated PTH and high serum calcium levels in the patient further support this diagnosis.
Chondroblastoma or giant cell tumor (GCT) of the bone is relatively common in adolescents or young adults, often presenting as an osteolytic lesion, especially in the epiphysis or metaphysis. However, such tumors are usually unilateral, and simultaneous involvement of both patellae is uncommon. Additionally, they correlate less strongly with the patient’s laboratory findings.
Metastatic lesions often appear as multiple osteolytic changes, usually in older patients or those with a known history of primary tumors. In this case, the patient is young, and no other lesion indicative of metastasis is present, making this possibility relatively unlikely.
Considering the patient is a 32-year-old female with bilateral osteolytic, expansile lesions of the patellae, subperiosteal bone resorption in both hands, elevated PTH and serum calcium measurements, and histopathological confirmation, the most likely diagnosis is Brown Tumor caused by hyperparathyroidism.
This diagnosis has been confirmed by histological findings and related laboratory tests. If further clarification of the gland’s anatomy or the nature of the abnormality is required, MRI or parathyroid nuclear imaging (e.g., 99mTc-MIBI scan) could be considered.
Treatment Strategy:
Rehabilitation and Exercise Prescription:
Throughout the rehabilitation process, a gradual, individualized approach should be followed, carefully assessing bone strength and patient tolerance to ensure safety.
The above report is a reference analysis based on the provided images and textual information and cannot replace an in-person consultation or professional medical opinion. Treatment and rehabilitation plans should be individualized and carried out under the guidance of qualified healthcare professionals.
Brown tumours in the patella.
