Anatomical variants in imaging

Anatomical variants in imaging

Anatomical variants in imaging

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Introductory Concepts - What's Normal-ish?

  • Anatomical Variant: A common, asymptomatic deviation from typical anatomy. Crucial to differentiate from true pathology to avoid misdiagnosis and unnecessary procedures.
  • Key Features: Usually discovered incidentally. Characteristically have well-defined, smooth borders and follow the signal/density of their parent tissue on all imaging sequences.
  • Common Examples: Azygos lobe, accessory spleen, developmental venous anomaly (DVA), persistent fetal circulation patterns.

⭐ Many variants are classic "leave-me-alone" lesions. Confident identification requires no follow-up.

CNS Variants - Brainy Quirks

  • Cavum Septum Pellucidum (CSP) & Vergae (CSPV): Midline CSF-filled cavities. Represents a failure of fusion of the septal leaflets. Common in neonates, usually fuses post-birth. A frequent, benign incidental finding in adults.
  • Mega Cisterna Magna: Focal enlargement of the subarachnoid space in the posterior fossa (vertical dimension >10 mm on midline sagittal). Crucially, the cerebellum and 4th ventricle are morphologically normal.
  • Pineal Cysts: Common, typically asymptomatic, and small (<1 cm). Found incidentally on MRI.

⭐ The primary clinical task is to differentiate these benign variants from pathological lesions like arachnoid cysts, epidermoid cysts, or cystic neoplasms which may require intervention.

Thoracic Variants - Chest Oddities

  • Azygos Lobe: Not a true lobe; an anomalous azygos vein creates a fissure, isolating a portion of the right upper lobe. Mimics a bulla or mass on CXR.
  • Pectus Excavatum: Sternal depression ("funnel chest"). Can displace the heart, obscuring the right heart border.
  • Pectus Carinatum: Sternal protrusion ("pigeon breast").
  • Poland Syndrome: Unilateral absence of pectoralis major muscle, often with ipsilateral syndactyly and breast hypoplasia.

⭐ In Pectus Excavatum, the apparent cardiomegaly and obscured right heart border on PA chest X-ray are artifacts of cardiac compression and rotation, a phenomenon known as "pancake heart."

Abdominopelvic Variants - Guts & Glory

  • Situs Inversus: Mirror-image reversal of organs. Dextrocardia on CXR is a clue. Associated with primary ciliary dyskinesia (Kartagener syndrome).
  • Accessory Spleen (Splenule): Common incidentaloma (~10-30% of patients), typically near the splenic hilum. Can be mistaken for a tumor.
  • Horseshoe Kidney: Fused lower poles get trapped under the Inferior Mesenteric Artery (IMA) during ascent. ↑ risk of stones & infection.

Meckel's Diverticulum: Most common GI congenital anomaly. 📌 Rule of 2s: 2% prevalence, 2 feet from ileocecal valve, 2 inches long, 2% symptomatic, presents by age 2.

Musculoskeletal Variants - Bony Bonuses

  • Accessory Ossicles: Unfused bone centers that mimic fractures. Differentiated by smooth, corticated borders.
    • Os Trigonum: Posterior ankle. Pain with plantar flexion (os trigonum syndrome).
    • Accessory Navicular: Medial foot. Can lead to painful tendinopathy.
  • Common Variants:
    • Fabella: Sesamoid in lateral gastrocnemius tendon.
    • Bipartite Patella: Unfused superolateral patellar pole. Often bilateral.

⭐ The fabella, a sesamoid bone in the gastrocnemius tendon, is present in up to 30% of individuals and can cause posterolateral knee pain.

Foot X-rays: Accessory ossicles and anatomical variants

High‑Yield Points - ⚡ Biggest Takeaways

  • Anatomical variants are common incidental findings, not true pathologies; recognition prevents misdiagnosis.
  • An azygos lobe is not a true accessory lobe but a fissure created by an aberrant azygos vein.
  • Accessory spleens (splenules) are frequent and can mimic lymphadenopathy or pancreatic/adrenal tumors.
  • A horseshoe kidney is the most common renal fusion anomaly, increasing risk for UPJ obstruction and stones.
  • A persistent left-sided IVC can be mistaken for para-aortic lymphadenopathy.

Practice Questions: Anatomical variants in imaging

Test your understanding with these related questions

A 75-year-old man presents to the clinic for chronic fatigue of 3 months duration. Past medical history is significant for type 2 diabetes and hypertension, both of which are controlled with medications, as well as constipation. He denies any fever, weight loss, pain, or focal neurologic deficits. A complete blood count reveals microcytic anemia, and a stool guaiac test is positive for blood. He is subsequently evaluated with a colonoscopy. The physician notes some “small pouches” in the colon despite poor visualization due to inadequate bowel prep. What is the blood vessel that supplies the area with the above findings?

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Flashcards: Anatomical variants in imaging

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In portal hypertension, the _____ vein backs up into the esophageal vein, resulting in varices

TAP TO REVEAL ANSWER

In portal hypertension, the _____ vein backs up into the esophageal vein, resulting in varices

left gastric

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