Saturday 27 August 2011

Radiotherapy induced fatty marrow

A 67 y o female ,  a known case of Ca cervix with radiotherapy. Now complains of severe backache, radiating to lower limbs. Referred to MRI lumbar spine to rule out metastasis and cause of pain. 
Here is her MRI Lumber spine; Sagittal T1, T2 and STIR sequences. 
Diffuse homogeneously high marrow signals involving L5 and all sacral vertebral bodies on T1 and T2 w images with complete signal suppression on STIR implies to fatty marrow, it s a radiotherapy induced change, area of involvement corresponds to field of radiotherapy, should not be mistaken for neoplastic marrow infiltration.
A benign looking osseous haemangioma in D12 vertebral body with typical vertical striations and faint high signals on STIR again not be mistaken for metastasis.
Her cause of backache appears to be the degenerative changes marked at L4-5 with anterior subluxation of L4 off L5.


Transformation of normal cellular marrow into fatty marrow after therapeutic irradiation.
Radiation destroys hematopoietic elements which are highly radiosensitive.

Location and size corresponds to site of irradiation and extent of radiation field with sharp demarcation between irradiated vs. untreated adjacent normal marrow.
Marrow signals are often homogeneously hyper intense on T1. Heterogeneity may be due to residual or recurrent marrow disease.
Signals on T2WI are high to intermediate.
Signals on STIR variable depending up on timing of radiation.
In acute phase may signals are high on STIR indicating marrow edema and necrosis. Marrow odema is maximum at around ninth after irradiation, followed by subsequent gradual decrease in SI. After complete marrow reconverstion signals are homogenously low on STIR owing to signal suppression.

Marrow changes on MRI dependent on radiation dose, fractionation, and time elapsed after treatment.
No change in marrow SI with radiation dose of 1.25 Gy
Between 20-30 Gy dose, partial recovery occur between 2-9 years and return to normal marrow after long term follow-up ~ it takes 10 yr
At 50 Gy, Complete and irreversible changes occur. Persistent fatty marrow even after 9 years.

Fatty marrow seen on MRI as early as 2 weeks after therapeutic irradiation. ~ 90% will show fatty marrow after 2 months. Marrow reconversion in pediatric patients occur 11-30 months after radiation treatment, takes relatively longer time.

Usually asymptomatic and requires no treatment.
There may be Pain, Myelopathy and radiculopathy due to associated problems like compression fracture or tumor infiltration which needs to fixed accordingly.

Reference : Osborn Diagnostic imaging.

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