Proximal radial pseudotumour: magnetic resonance imaging appearances and prevalence

A pseudo-tumour could be defi ned as an abnormality that resembles a tumour but with an absence of neoplastic cells. Many pseudo-tumours have been described in the radiology literature [1], some of which relate to marrow signal abnormalities that present as potential interpretational pitfalls. Marrow signal abnormalities are becoming increasingly frequent dilemmas given the burgeoning use of fat suppressed imaging. The bone marrow is a complex organ whose proportions can vary greatly depending upon site and age [2,3], with typical conversion of yellow to red marrow in long bones occurring from the end of the bone to the central diaphyseal region [4]. Some studies have demonstrated that variations in this process exist [5]. However, islands of red marrow can persist from the original conversion stage into adulthood [3]. Multiple studies have been conducted looking at red marrow MRI signal around the knee joint in an attempt to assess its frequency and its clinical signifi cance [68]. The presence of this red marrow has been assessed against patient factors such as weight, age, sex, haemoglobin levels and smoking. The elbow is a less frequently imaged joint than the knee but there have been observations with regards to alteration of marrow signal around the elbow, particularly in the distal humerus [9]. The purpose of the current study was to assess the incidence of this imaging feature at the elbow joint, particularly within the proximal radius following several cases referred to our institution with potential diagnoses of occult fracture, stress injury, reactive marrow oedema, osteitis and osteomyelitis.


3T (Philips
Studies were excluded if the proximal radius was not included in the imaged fi eld (n=3), if marrow signal was obscured by metal artifact (n=3) or if the proximal radius was involved by any pathological process involving the marrow (n=4). Four cases had pathology at the radial tuberosity aff ecting the adjacent marrow as follows; cystic change underlying the cortex of the radial tuberosity secondary to distal biceps tendinosis, cortical erosion and marrow-oedema-like SI in the radial tuberosity secondary to bicipitoradial bursitis, two cases of neoplastic marrow infi ltration due to histologically proven leiomyosarcoma, and multiple lesions consistent with Brown tumours in patient with known hyperparathyroidism.
Univariate analysis to assess for association between age, sex, side and the presence of a pseudo-tumour was undertaken. A p-value of <0.05 was taken as statistically signifi cant.

Results
Of the 100 successive elbow MRI cases identifi ed, 10 were excluded. Therefore, the fi nal study group comprised of 90 patients, 43 males and 47 females with a mean age of 41 years and age range of 7-80 years.
There were 11 (12.2%) patients imaged at 1.5T and 79 (87.8%) at 3T. Proximal radial pseudo-tumours were identifi ed in 7 (7.8%) patients (Figures 1-5), 3 males and 4 females (p= 0.79). Pseudo-tumours involved the right elbow in 6 cases and left elbow in 1 (p=0.08). Age range for pseudo-tumour was 7-65 years with mean age 30 years, compared with 5-80 years with mean 42 years for no pseudo-tumour (p=0.1). The pseudotumours measures between 5 to 38mm in length with a mean of 21mm, and the distance from the radial articular surface varied from 4 to 32mm with a mean of 16mm. None of the pseudotumours was associated with cortical abnormality, active periostitis or soft tissue oedema-like SI. No abnormal marrow SI was identifi ed in the distal humeral metaphysis or proximal ulna on any of the imaging series.

Discussion
Bone marrow is regarded as a dynamic organ and undergoes lifelong changes, with the capability to reverse these changes when placed under certain stresses [10]. It is this ability that renders bone marrow susceptible to changes as a result of not only metabolic stimulation, but also hyperactive osteoclastic activity. This can result in a pseudo-tumour appearance as

Reconversion of yellow to red marrow is considered to occur in an opposite longitudinal direction to its initial conversion, with reconversion widely accepted to begin in the ends of long bones then extending to the middle or central diaphyseal regions [4].
It is also accepted that there may be residual red marrow at the last conversion sites, which are in the proximal metaphyses of the femur and humerus. It is well-documented that these residual red marrow foci can show wide variation in location and morphology across the ages at these sites [3], but there is little literature on red marrow at sites other than these, such as around the elbow joint. This rarity of marrow signal abnormality in and around the elbow joint is confi rmed in a study that had only 1 elbow MRI study with a report of incidentally noted 'abnormal or heterogenous marrow signal' out of a total of 49,678 MRI studies [11]. A more recent study suggested wide variation in red marrow signal with diaphyseal marrow reconversion appearing to precede that of distal metaphyseal marrow in the femur [5]. Focal nodular hyperplasia of red marrow has been described as an abundance of focal red marrow due to aberrant red to yellow marrow conversion [12]. It is described as a rarely occurring localised form in the marrow of the spine and pelvis, compared to regional forms around the knees of endurance athletes, heavy smokers and in obesity [13]. Therefore, it is important to recognise aberrant marrow signal intensity as highlighted in our current study, and we postulate that this proximal radial

Conclusion
The proximal radial pseudo-tumour is seen in approximately 8% of elbow MRI studies, and should be recognised as a variant of proximal radial marrow signal. The increasing use of MRI will undoubtedly result in more incidental fi ndings and documentation of the incidence and basic MRI imaging features at this location should increase confi dence in MRI assessment and reduce the requirement to undertake needle biopsy for tissue diagnosis in this non-neoplastic condition.