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How Common are Bone Islands on Abdominal and Pelvic CT?

Tamar Sella MD Nurith Hiller MD Azraq Yusef MDEugene Libson MDJacob Sosna MD

Dept. of Radiology Hadassah Hebrew University Hospital, JerusalemDept. of Radiology Hadassah Hebrew University Hospital, Jerusalem

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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

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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?

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Bone Islands - Frequency

The exact frequency is unknown

Prevalence estimated as 0.6-1.4% 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.

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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

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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)

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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.

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Referral for CT

Evaluate abdominal pain 137

Suspected renal colic 89

Other non-cancer related indication 37

Total 263

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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

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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%) 46%

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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).

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Results

BI location:iliac bone 16.7%acetabulum 20.5%sacrum 16.7%femur 27.3%ischium 5.5%vertebrae 8%pubic bone 5%

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Conclusion

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

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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.

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