Radiation-induced changes in the bone marrow

Clinical History

A 52-year-old female patient presented for the first follow-up 6 months after she had been treated for a mucoid liposarcoma anterior to the proximal medial tibia. The treatment included surgery and radiotherapy (50 Gy in 2 Gy fractions). The patient was asymptomatic.

Imaging Findings

MR imaging of the lower extremity at the site of previous operation and irradiation was performed. Multiple focal changes with intermediate signal on T1-w (Fig. 1), moderately increased signal on fluid sensitive sequence (Fig. 2) and moderate enhancement on fat-suppressed contrast enhanced T1-w images (Fig. 3) were disclosed.

Discussion

A. Radiation-induced changes in the bone marrow are very common and include fatty replacement, pathologic fractures, avascular necrosis, focal lesions of abnormal signal on MR imaging and rarely development of sarcoma [1, 2, 3]. Depending on the age of the patient and the amount of radiation, some changes may be reversible or not [4].

B. Clinical symptoms are usually absent with the exception of insufficiency fractures which occur in about 6% of cases [5]. The radiation-induced changes are mostly found during follow-up imaging. Careful attention should be paid to rule out the possibility of metastases.

C. MR imaging is the method of choice for assessing the bone marrow. During the first three days following irradiation (acute phase) the bone marrow undergoes excessive oedema which results in areas of reduced signal in T1-w and high signal on fluid sensitive MR images [4]. Between the third and the sixth week the bone marrow appears heterogeneous on T1-w MR images due to fatty replacement. After the sixth week, the lesions appear with high signal on T1-w images (in older patients), or with a region of central high signal and a peripheral intermediate one, due to haematopoietic regeneration (in younger patients) [6]. Many of those lesions may raise suspicion of recurrence. However, the absence of signs typical for metastatic deposits matched with the clinical picture of the patient, should help the radiologist to arrive at a final diagnosis of treatment-related changes. In inconclusive cases, a biopsy might be required, which, however, is invasive and may be complicated with fracture or infection [7]. In our case, the consecutive follow-up MR imaging studies up to 24 months after radiation showed no differences in the bone marrow changes suggesting the correct diagnosis.

D. No therapeutic procedure is needed. Nevertheless, follow-up MR imaging of the affected area must be required in inconclusive cases, in order to confirm their benign nature.

E. It is essential to recognize and differentiate post-radiation changes in the bone marrow from metastatic deposits in order to avoid unnecessary diagnostic tests and potentially harmful treatment.

Differential Diagnosis List

Final Diagnosis

Radiation-induced lesions of the bone marrow.

URL:	https://www.eurorad.org/case/12593
DOI:	10.1594/EURORAD/CASE.12593
ISSN:	1563-4086