Role of MRI in Acute Leukaemia, in a 7 year old with back pain

Clinical History

A 7-year-old boy presented with a four-week history of thoracic/lumbar back pain, intermittent abdominal discomfort and pyrexia. He was tender in the mid thoracic, paraspinal areas and L3-L4. Initial investigations revealed pancytopenia with a raised ESR. MRI of his spine was crucial in establishing a diagnosis.

Imaging Findings

First line imaging, abdominal X-Rays and USS, were normal. In view of his back pain and suggestion of marrow involvement (pancytopenia), MRI of thoracolumbar spine was performed.

T1 weighted images showed diffuse low signal intensity within the vertebral bodies, highlighted when compared to the adjacent intervertebral discs (Fig. 1).

Conversely on STIR imaging the marrow demonstrated increased signal intensity, compared to the adjacent muscle (Fig. 2).

Also noted was mild anterior wedging of the T7 end plate, due to superior end plate infraction. Similarly, minor increased signal at the inferior end plate of T8 and superior end plate of L1 was seen on T2 and STIR images.

Overall the images suggested a diffuse proliferative marrow disorder and bone marrow biopsy subsequently yielded a diagnosis of Acute Lymphoblastic Leukaemia (ALL).

Three month, post-treatment thoracolumbar X-rays show osteoporosis, loss of lumbar lordosis, and compression fractures of L5, 3, 2, 1 and T11. (Fig. 3)

Discussion

ALL is the most common malignancy of children. It has a myriad of clinical features that result from the process of marrow infiltration and replacement. These include immunosuppression, anaemia, bruising, fatigue, bony pain from vertebral fractures, abdominal swelling from hepatosplenomegaly and CNS manifestations.

Increasingly MRI is proving an invaluable tool in the initial investigations of these patients due to its ability to analyse a large volume sample of the marrow non-invasively [1].

The pattern of marrow signal seen in MRI i.e. diffuse involvement, variegated involvement or localised can be highly sensitive for delineating the overall underlying disease process [1].

In the acute leukaemias there is a diffuse pattern observed throughout the marrow. On T1 images there is a diffuse decrease in signal intensity, rendering the discs brighter by comparison [1]. Difficulty in interpretation arises in younger patients, however, as this diffuse low intensity signal on T1 may be hard to distinguish from red cell marrow, which is yet to convert to yellow marrow [2]. T2 / STIR imaging, however, grants the abnormal marrow increased signal intensity, showing it enhanced in comparison to the discs [1]. Hence, whenever vertebral T1 signal is lower than that of the adjacent disc, the radiologist should be alerted to a bone marrow pathology.

In our case some vertebral wedging was seen indicating important skeletal involvement. The prognostic outcome for skeletal involvement at diagnosis remains unclear. Wedging is usually multi-factorial due to both the disease process and steroids provided during treatment. Vertebral compression fractures, however, have been shown to undergo remodelling once remission is achieved and do not usually result in any neurological/functional compromise [3].

MRI has become an increasingly useful tool in diagnosing, staging and assessing response to treatment in leukaemia. There is hope in the future that serial MRI post chemotherapy for patients with ALL would obviate the need for repeated biopsy, though its use in assessing treatment response in other leukaemias, such as Acute Myeloid Leukaemia (AML) remains debatable [3].

However, it must be emphasised that although MRI will demonstrate diffuse involvement of the marrow suggestive of ALL, it is not specific to ALL alone. Diagnosis depends on ultimately on bone marrow histology coupled with morphology, phenotyping, cytogenetics and immunology.

Differential Diagnosis List

Final Diagnosis

Acute lymphoblastic leukaemia

URL:	https://www.eurorad.org/case/10230
DOI:	10.1594/EURORAD/CASE.10230
ISSN:	1563-4086