Introduction
That first night of Emergency Radiology On-Call is a rite of passage—a blend of excitement and sheer terror. You’re the final line of defense, and while you can’t know everything, you must know the things that will kill a patient in the next hour.
Our goal at Radiobite is simple: Survival.
We’ve distilled the mountain of urgent pathology down to the absolute five most critical, high-stakes diagnoses every junior resident must recognize immediately. Master these, and you’ve conquered the night.
1. Acute Aortic Syndromes (AAS): The Great Mimicker 💔
AAS, primarily Aortic Dissection (Type A), is a surgical emergency demanding immediate recognition. These cases often present with non-specific chest or back pain, and a negative ECG is not reassuring.
What to Spot (The “Aorta Protocol” CTA):
- Intimal Flap: The hallmark. Look for a linear filling defect separating the true and false lumens.
- True vs. False Lumen: The false lumen is usually larger and may show a “beak sign” (a crescent of enhancing mural thrombus).
- Periaortic Hematoma: Look for fluid/hematoma surrounding the aorta.
- Complication: Check for malperfusion—is the dissection compromising flow to the coronary arteries, carotids, or renal arteries?
🚨 On-Call Action Point: If you see a Type A Dissection (involving the ascending aorta), call the attending and the cardiothoracic surgery team immediately. Patient management is time-critical.
2. Epidural and Subdural Hematomas (EDH/SDH): Neuro-Trauma Time Bomb 🧠
Head CTs are ubiquitous on call. Your task is to quickly differentiate a potentially less urgent bleed from one requiring immediate neurosurgical intervention.
What to Spot (Trauma Head CT):
- Epidural Hematoma (EDH): Typically lenticular (lens-shaped) and biconvex. It is often associated with a skull fracture (temporal bone) and does not cross suture lines. It’s a high-pressure arterial bleed.
- Subdural Hematoma (SDH): Typically crescent-shaped and concave. It is a venous bleed that crosses suture lines but is limited by the falx and tentorium. It is usually more chronic and insidious.
- Midline Shift: This is the most critical sign. Even a small EDH/SDH with significant mass effect (herniation, effacement of basal cisterns, midline shift ≥5 mm) is an emergency.
🚨 On-Call Action Point: Document the side, size, and most importantly, the millimetres of midline shift. Anything that suggests imminent herniation requires an urgent neurosurgery consult.
3. Acute Appendicitis: The Most Common Surgical Belly 🔪
While not as immediately fatal as an aortic tear, a perforated appendix is a morbidity disaster and the most common cause of non-traumatic acute abdomen on call. Your job is to make the diagnosis or exclude it with certainty.
What to Spot (Abdominal CT with IV Contrast):
- Dilated Appendix: Appendix diameter greater than 6 mm is the classic sign.
- Wall Enhancement: The inflamed appendix wall will show avid contrast enhancement.
- Peri-Appendiceal Stranding: Look for fat stranding, inflammation, or an abscess collection around the appendix.
- Appendicolith: A calcified fecalith within the appendix lumen may be visible and suggests obstruction.
🚨 On-Call Action Point: If you are unsure, avoid calling it “equivocal.” Look for secondary signs (terminal ileal wall thickening, reactive adenopathy) and be prepared to recommend a short follow-up scan or clinical correlation if the patient is otherwise stable.
4. Testicular Torsion: The 6-Hour Window ⏳
This is the ultimate “stat” ultrasound, especially in an adolescent male presenting with acute scrotal pain. The viability of the testicle depends on rapid diagnosis—you have about six hours before viability drops sharply.
What to Spot (Scrotal Ultrasound with Doppler):
- Whirlpool Sign: Twisting of the spermatic cord (less common for a junior resident, but a pathognomonic sign).
- Absent Blood Flow: The critical finding. The affected testis will show absent color Doppler flow, while the contralateral testis will have normal flow.
- Morphology: The affected testis is usually enlarged and hypoechoic (darker) compared to the contralateral side.
🚨 On-Call Action Point: Call the Urology team immediately if blood flow is absent or severely decreased, even before the attending. This is a surgical emergency where minutes count.
5. Ectopic Pregnancy: Hemoperitoneum in a Young Woman 🤰
A ruptured ectopic pregnancy is a life-threatening cause of shock and sudden death in women of childbearing age. It is often the first differential for lower abdominal pain.
What to Spot (Transvaginal Pelvic Ultrasound):
- Positive β-hCG: Always correlate with lab work.
- No Intrauterine Pregnancy (IUP): You cannot see a gestational sac within the uterus.
- Adnexal Mass: Look for a non-cystic, complex mass (e.g., ring of fire sign—a hypervascular ring) adjacent to the ovary.
- Free Fluid (Hemoperitoneum): The most dangerous sign. Look for anechoic (black) or complex fluid in the Pouch of Douglas, paracolic gutters, or hepatorenal space (Morrison’s Pouch). Significant fluid suggests rupture.
🚨 On-Call Action Point: If you see free fluid with a positive β-hCG and no IUP, call the OB/GYN service and your attending immediately. This patient needs a rapid surgical consult and possible emergent laparotomy.
Conclusion
Your first night on call is about mastering the critical five and knowing when to escalate. Don’t try to be the hero who knows every zebra; be the confident resident who never misses a killer common diagnosis.
