MRI patterns indicate treatment success and tumor relapse following radiofrequency ablation of osteoblastoma

Figures & data

Figure 1. Flow diagram of the study cohort.

Table 1. Data overview of the study group.

Patient number	Ablation number	Age/sex	Location	Joint involved?	Largest diameter (mm)	Central mineralization?	Shape	Needle position number	Recurrence? [time to recurrence (m)]	Number of follow-up MRIs (total/early (1–4 m)/ late (9–72 m)	MRI follow-up period (m)	Mean interval between follow-up MRIs (m)
1	1	12/M	Femur	No	15	Yes	Ellipsoid	1	No	3/0/3	74–131	29
2	1	16/M	Humerus	No	15	Yes	Ellipsoid	2	Yes [11]	1/1/0	1	/
	2							1	Yes [5]	2/1/0	4	2
	3							1	No	1/1/0	3	/
3	1	17/M	Scapula	Yes	16	Yes	Spherical	2	No	3/1/2	3–16	7
4	1	14/M	Tibia	No	17	Yes	Ellipsoid	2	No	1/1/0	3	/
5	1	8/F	Hip	Yes	15	Yes	Ellipsoid	2	No	4/1/3	4–33	10
6	1	18/M	Tibia	No	17	Yes	Spherical	2	No	2/1/1	3–21	18
7	1	28/F	Spine	No	15	Yes	Spherical	2	No	1/1/0	1	/
8	1	36/M	Scapula	Yes	15	Yes	Spherical	2	No	1/1/0	3	/
9	1	3/F	Tibia	No	18	Yes	Ellipsoid	2	Yes [33]	3/0/3	23–33	5
	2							2	Yes [26]	4/1/3	3–26	8
	3							4	No	2/1/1	3–8	5
10	1	20/M	Hip	Yes	20	Yes	Ellipsoid	6	No	2/2/0	1–3	2
11	1	46/M	Femur	No	23	Yes	Ellipsoid	4	No	5/0/5	9–51	11
12	1	16/M	Tibia	No	17	Yes	Ellipsoid	1	No	2/1/1	3–9	6
13	1	48/M	Humerus	Yes	21	Yes	Ellipsoid	4	No	3/1/2	3–15	6
14	1	10/M	Sacrum	Yes	16	Yes	Ellipsoid	3	No	2/1/1	1–16	15
15	1	11/F	Femur	No	16	Yes	Ellipsoid	2	No	2/1/1	3–11	8
	19	20.2		6/15	17.1	15/15	E: 11/15	2.4	4/19 [18.8]	44/17/26	1–131	9.4

mm: millimeters; m: months.

The bold number indicate the sum/ average of the column values where appropriate.

Table 2. MRI protocol for osteoblastoma examinations in our department.

	Repetition time (ms)	Echo time (ms)	Voxel size (mm)	Field of view (mm)	Matrix
Coronal STIR	7760	48	0.99 × 0.99 × 4	379 × 379	346 × 384
Coronal T1 SE	600	12	0.74 × 0.74 × 4	380 × 380	435 × 512
Sagittal T2 TSE	7780	92	0.78 × 0.78 × 3.3	400 × 300	384 × 512
Axial T2 fat-saturated	4960	72	0.71 × 0.71 × 3.3	320 × 287	448 × 402
Coronal T1 SE ce	600	12	0.74 × 0.74 × 4	380 × 380	435 × 512
Axial T1 fat-saturated ce	940	11	0.99 × 0.99 × 3.3	319 × 319	384 × 384

STIR: short tau inversion recovery; SE: spin-echo; TSE: turbo spin-echo; ce: contrast-enhanced; ms: milliseconds; mm: millimeters.

Figure 2. Graphical illustration of the imaging patterns of osteoblastoma after ablation. The linear black and gray pattern represents edema or enhancement. The white signal represents normal bone marrow signal. CNE: central nidus enhancement; PNE: peripheral nidus enhancement; PBME: perifocal bone marrow edema; FNC: fatty nidus conversion.

Figure 3. Images of an 8-year-old female with a successfully treated osteoblastoma of the left acetabulum. (a) Axial T₁-weighted fat-saturated contrast-enhanced image taken at the time of diagnosis showing strong enhancement of the nidus (thick arrow) with extensive perifocal edema. (b) Axial reformation of the CT scan taken during the RFA procedure showing the needle tip in the nidus. (c–e) Follow-up axial T₁-weighted fat-saturated contrast-enhanced images taken at 4, 9 and 21 months post-RFA. (c, d) A target-like appearance (thin arrows) is seen after 4 and 9 months. (e) Disappearance of the peripheral nidus enhancement and perifocal edema after 21 months. (f, g) Follow-up coronal T₁-weighted images taken at 4 and 21 months post-RFA showing fatty conversion of the nidus (arrowheads) over this period. RFA: radiofrequency ablation.

Figure 4. Images of a 10-year-old male with a successfully treated osteoblastoma of the right sacrum. (a) Axial short tau inversion recovery image taken before RFA showing a hyperintense nidus (thick arrow) with extensive perifocal edema. (b) Axial reformation of the CT scan taken during the RFA procedure showing the RFA needle tip in the nidus and an epidural needle for thermal protection. (c, d) Follow-up axial T₁-weighted fat-saturated contrast-enhanced images taken at 1 and 16 months post-RFA. (c) A typical post-RFA pattern of a target-like appearance (thin arrow) is seen after 1 month. (e) Disappearance of the peripheral nidus enhancement (arrowhead) and perifocal edema after 16 months. (f) Follow-up coronal T₁-weighted images of the same MRI as in (e) taken 16 months after RFA showing fatty conversion of the nidus (arrowhead). RFA: radiofrequency ablation.

Table 3. Morphological follow-up MRI pattern of successfully treated osteoblastoma patients.

Non-recurrence	Number of patients	Number of exams	CNE	PNE	PBME	FNC	Target-like appearance
Early follow-up MRI (1–4 m)	13	14	0% (0/14)	93% (13/14)	71% (10/14)	0% (0/14)	100% (14/14)
Late follow-up MRI (8–131 m)	10	20	0% (0/20)	20% (4/20)	20% (4/20)	55% (11/20)	25% (5/20)

MRI follow-up exams were divided into an early group comprising exams performed 1–4 months after RFA and a late group comprising exams conducted 8–131 months after RFA. MRI exams performed after RFA procedures that resulted in recurrence are not included in this chart.

CNE: central nidus enhancement; PNE: peripheral nidus enhancement; PBME: perifocal bone marrow edema; FNC: fatty nidus conversion; m: months.

Figure 5. Images of a 16-year-old male with a recurrent osteoblastoma of the right humerus. (a) Coronal reformation of a CT scan performed at the time of diagnosis. (b) Axial T_2-weighted fat-saturated image taken at the time of the second clinical recurrence showing extensive perifocal bone marrow edema and the former drilling channel (thick arrow) located cranially and laterally to the recurrent active nidus. (c) Coronal T₁-weighted fat-saturated contrast-enhanced image of the same exam as in (b) showing strong contrast enhancement of the central nidus (arrowhead). (d) Coronal reformation of a CT scan performed at the time of the second recurrence showing an active centrally mineralized nidus (arrowhead) in the cranial segment of the initial osteoblastoma. (e, f) Coronal and axial T₁-weighted fat-saturated contrast-enhanced images taken 3 months after the third RFA. A typical target-like appearance is seen with a non-enhanced central nidus surrounded by an enhanced peripheral nidus (thin arrows). Only a small degree of perifocal bone marrow edema is visible. RFA: radiofrequency ablation.

Table 4. Morphological follow-up MRI pattern at the time of clinical osteoblastoma recurrence after RFA.

Patient number	Ablation number	MRI at the time of recurrence available?	Time after last RFA (m)	CNE?	PNE?	PBME?	FNC?
2	1	No	–	–	–	–	–
	2	Yes	5	Yes	Yes	Yes	No
9	1	Yes	33	Yes	Yes	Yes	No
	2	Yes	26	Yes	Yes	Yes	No

RFA: radiofrequency ablation; CNE: central nidus enhancement; PNE: peripheral nidus enhancement; PBME: perifocal bone marrow edema; FNC: fatty nidus conversion.