Osteoblastoma of the tibia that debuts as juxta-cortical osteolytic tumour

A 56-year-old male with a 1-year history of left leg pain that wakes him up at night. Pain has become constant over the last month.

No trauma was referred. No other relevant symptoms.

An x-ray, MRI and CT-guided biopsy were performed.

The frontal x-ray showed an intraosseous osteolytic lesion in the left tibia (type 1b geographic patron) with a thick continuous periosteal reaction (Figure 1a). The lateral projection showed the true location of the lesion sitting in the posterior cortex of the tibial diaphysis without medullary extension (Figure 1b) and with a narrow transition zone, indicative of a non-aggressive nature.

In the MRI, the lesion demonstrated no soft tissue mass. The bone findings consisted of the juxta-cortical lesion with peripheral oedema surrounding the bone marrow and soft tissues around the tibia (Figures 2a and 2b).

CT showed a cortical-based lesion with a solid periosteal reaction. The CT-guided biopsy confirmed the diagnosis of osteoblastoma (Figure 3A and 3B).

Osteoblastomas are bone-forming tumours that account for 3% of all benign bone tumours [1]. Predominantly, affects young adults in the second decade of life, although it can appear at any age, with men’s predilection [2].

In the past, osteoblastomas and osteoid osteomas were classified as variants of a single tumour. Nowadays, these are considered two tumours that differ in location, clinical and radiological presentation and potential for progression [3].

Osteoblastoma is commonly located in the axial bones, whereas osteoid osteoma arises in the long bones. Osteoblastoma typically manifests as gradual, persistent pain that often does not alleviate with nonsteroidal anti-inflammatory drugs (NSAIDs), whereas the nocturnal pain characteristic of osteoid osteoma commonly shows significant improvement with NSAIDs [3].

Lesion size is a discriminating criterion, with osteoid osteoma being less than 1.5–2 cm in diameter and osteoblastoma having the potential to become larger (> 2 cm). In x-ray, osteoblastoma may have a bubbly appearance and internal calcification. It can associate soft tissue mass, cortical destruction and secondary aneurismal bone cyst-like changes in 20% [2,3]. CT can add matrix-related information, and although MRI may give some nonspecific information and tend to overestimate the lesion, it can be useful in describing bone and soft tissue oedema [4].

Based on the juxta-cortical location observed on radiography, differential diagnoses of metastasis, intracortical abscess, and benign primary tumour were entertained. While osseous metastases are notably more prevalent than primary osseous tumours, no prior history of malignancy was documented in this case. Furthermore, metastases typically manifest as multiple lesions, primarily affecting the axial or proximal appendicular skeleton. Additional signs include pathological fractures, soft tissue components and a broad transition zone suggestive of aggressive growth [5].

The subperiosteal abscess is a rare complication of bone infection and is more frequent in epiphyseal and subchondral locations secondary to intra-articular infection extending to the bone [6].

The continuous periosteal reaction and the area of central radiolucency with a narrow transition zone oriented the diagnosis towards a non-aggressive lesion. The diameter greater than 2 cm, the oval morphology and the oedema of the medullary bone and adjacent soft tissues suggested the diagnosis of osteoblastoma, which was confirmed after biopsy.

The patient was treated surgically with en bloc resection and remains asymptomatic 3 years later.

The most effective treatment is surgery. Preoperative embolisation is an adjuvant therapy but not chemotherapy or radiotherapy  [7,8]. The risk of recurrence is from 15% to 25%.