1. How Common are Bone Islands on Abdominal and Pelvic CT?
Tamar Sella MD
Nurith Hiller MD
Azraq Yusef MD
Eugene Libson MD
Jacob Sosna MD
Dept. of Radiology Hadassah Hebrew University Hospital, Jerusalem

2. Bone Islands - Background
focus of compact bone located in cancellous bone
also known as an enostosis, endosteoma, calcified medullary defect
a benign entity that is usually found incidentally on imaging studies
bone islands may mimic a more agressive process, such as an osteoblastic metastasis

3. Bone Islands - Pathophysiology
exact etiology of bone islands is not clear
Most likely developmental in nature: cortical bone that has failed to undergo medullary resorption
Histologically, bone islands are intramedullary foci of normal compact bone with haversian canals and "thorny" radiations that merge with the trabeculae of surrounding bone
Hamartoma?

4. Bone Islands - Frequency
The exact frequency is unknown
Prevalence estimated as % based on plain radiographs
May be found in any osseous site; however, most commonly identified in the pelvis, long bones (most commonly proximal femur), also fairly common in ribs, and spine.

5. Bone Islands – Plain films
round or ovoid intramedullary sclerotic foci
Do not extend beyond the cortex
The long axis typically parallels the long axis of the involved bone
Homogeneously sclerotic with “thorny” radiating bone spicules that extend from the center of the lesion and blend with the trabeculae
1 mm to 2 cm in diameter; size generally remains stable

6. Purpose
The frequency of bone islands has been reported based on plain films only
Where digital workstations are used, bone windows are now routinely reviewed on every CT scan
To determine the frequency of small sclerotic lesions, most probably bone islands, on routine abdominal and pelvic CTs (AP CTs)

7. Patients and Methods
We prospectively examined AP CT scans of 263 consecutive patients referred over a 6 month period
Patients had no history of neoplastic disease or trauma
Focal sclerotic round or oval lesions in the medulla of the bone were recorded.
Data collected included size, location, and number of lesions per patient.

8. Referral for CT Evaluate abdominal pain 137 Suspected renal colic 89
Other non-cancer related indication 37
Total
263

9. Patients and Methods
For demographic purposes, patients were divided into three age groups:
40 years or younger
41-60 years
61 years or above
Data was analyzed for the whole study population as well as for each age group

10. Results 132 males (50%) 131 females (50%) BI found in 118 pts = 44.8%
Age group
# of patients
Incidence of BI
≤ 40
35 (29.6%)
46%
41-60
41 (34.7%)
44.5%
≥ 61
42 (35.5%)

11. Results A Total of 161 BIs found in 118 pts single BI - 71%
two BI - 21%
three BI - 8%
Size ranged from 1-13mm (mean 7mm, median 7mm).

12. Results BI location: iliac bone 16.7% acetabulum 20.5% sacrum 16.7%
femur %
ischium %
vertebrae 8%
pubic bone 5%

13. Conclusion
BI are detected much more commonly on CT than previously reported on plain radiographs – 44.8%

14. Work in progress
Our study evaluated the incidence of BI in a general population (low risk).
However, these lesions may cause confusion when incidentally found, mostly in oncology patients .
Management guidelines need be established, taking in account their relatively high incidence.
The incidence in an oncologic subset of patients is in evaluation.

15. Thank You