Suspected Appendicitis at 18 Weeks' Gestation: Consent, Dose, and Protocol Optimization
A 26-year-old woman at 18 weeks' gestation presents at 21:00 with 14 hours of right lower quadrant pain, nausea, and a temperature of 37.9 °C. White cell count is 13,500/µL and C-reactive protein is elevated. Graded compression ultrasound shows a normal right ovary and no free fluid, but the appendix is not visualized, and the sonographer notes a body habitus that limits the examination. The surgical team requests CT of the abdomen and pelvis with IV contrast to exclude appendicitis before deciding on laparoscopy. The patient is tearful and asks whether the scan will harm her baby. There is no on-site physicist, and the department's protocol book lists a routine adult abdomen/pelvis study with a single portal venous phase at 120 kVp.
1. How would you estimate and explain the fetal risk to this patient, and how does it compare with the alternative?
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Give the patient a real number and a real comparison rather than a reassurance she cannot evaluate.
- Dose: a modern single-phase CT abdomen/pelvis at 18 weeks typically delivers a fetal dose in the range of roughly 10–25 mGy, depending on the protocol; poorly optimized multiphase studies can exceed that. For context, deterministic effects such as malformation or pregnancy loss have a threshold around 100 mGy, so this is well below it.
- Risk: the main theoretical concern is a small increase in childhood cancer risk, on the order of 0.006% per mGy - a fraction of a percent at these doses. Say plainly that the risk is small but not zero.
- Compare it with the alternative: untreated appendicitis in pregnancy carries a substantial risk of perforation, preterm labour and fetal loss, and that risk rises with delay. A CT that changes management may reduce overall risk to both mother and fetus.
- Mention MRI as a reasonable alternative if it is available promptly and the patient prefers it, while noting that access and interpretation may delay care.
2. List the protocol modifications you would make to the department's routine study and explain the reason for each.
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Optimize the protocol rather than skip the study.
- One phase only: a portal venous phase at 70–90 seconds answers the appendicitis question; arterial and delayed phases add dose without adding diagnostic value here.
- Limit the scan range to the region of interest - from the upper abdomen to the pubic symphysis or less - since DLP scales linearly with irradiated length.
- Lower kVp to 100 with tube current modulation and iterative reconstruction; iodine conspicuity improves and dose falls.
- Avoid oral contrast (it delays care and is unnecessary) and use the smallest IV contrast volume that gives adequate enhancement.
- Shielding: a lead apron over the abdomen does not protect the fetus from internal scatter produced inside the mother and can interfere with automatic exposure control; it is generally not used. Say this rather than applying a shield for appearances.
- Do not repeat the acquisition for minor technical reasons; review images before the patient leaves the scanner.
3. Who should obtain consent, what must the conversation cover, and what has to be documented afterward?
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Informed consent and documentation are part of the examination, not paperwork after it.
- Who talks to her: the radiologist should speak with the patient, and document the conversation, before the scan; the technologist reinforces and confirms understanding but should not be the only person obtaining consent for a study involving fetal exposure.
- What the conversation covers: the clinical question, why ultrasound was insufficient, the estimated fetal dose and its comparison with the 100 mGy deterministic threshold, the small cancer risk, the alternative of MRI and its limitations, and the risk of not imaging. Record that she understood and agreed.
- Coordinate with the surgeons: confirm that the CT result will change management that night; if they would proceed to laparoscopy regardless, the scan is not justified.
- After the scan: document the protocol, CTDIvol, DLP and scan length, and estimate the fetal dose so it is available for obstetric counselling. If the dose estimate is uncertain, involve the medical physicist rather than guessing.