Case Author(s): Jeff Chesnut, D.O. and Keith Fischer, M.D. , 5/20/99 . Rating: #D3, #Q4

Diagnosis: 32-week intrauterine pregnancy imaged on bone scan

Brief history:

31 year old female undergoing metastatic work-up for breast carcinoma.

Images:

Anterior and posterior dual intensity images from bone scintigram are shown.

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Full history/Diagnosis is available below

Diagnosis: 32-week intrauterine pregnancy imaged on bone scan

Full history:

This patient is a 31 year old female with a 32-week intrauterine pregnancy and newly diagnosed breast carcinoma. A bone scintigram was obtained to evaluate for skeletal metastases.

Radiopharmaceutical:

Tc-99m MDP

Findings:

An amorphous area of increased activity is seen in the upper pelvis and abdomen representing the vascular placenta and uterine wall. No osseous metastases are seen.

Discussion:

Bone scintigraphy is rarely required during pregnancy and should be discouraged unless necessary. In this case, the oncologist felt is was necessary to evaluate for skeletal metastases prior to deciding on a regimen of chemotherapy.

Methylene diphosphonate, the agent used for bone scintigraphy, does not cross the placenta. The radiation dose to the fetus comes from transplacental radiation, radiation from the adjacent urinary bladder, and from any free Tc-99m pertechnetate (which does cross the placenta) that may be in the system. The fetus receives about 0.01 Rad/mCi of administered dose. This patient received 21.6 mCi of Tc-99m MDP so the average fetal dose, in this case, was approximately 0.22R. The patient was encouraged to push oral fluids and void frequently to further reduce fetal radiation exposure.

Major teaching point(s):

1. While bone scintigraphy is discouraged during pregnancy and lactation, it may be performed if necessary.

2. The Tc-99m MDP does not cross the placenta. Radiation exposure is transplacental, from the urinary bladder, and from any systemic free Tc-99m pertechnetate.

3. The average fetal dose is approx. 0.01R/mCi administered dose. This exposure may be minimized by hydrating the patient and having her void her bladder frequently.

ACR Codes and Keywords:

References and General Discussion of Bone Scintigraphy (Anatomic field:Genitourinary System, Category:Normal, Technique, Congenital Anomaly)

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Case number: bs097

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