Thursday, December 20, 2018

MRI Hepatic Lesion Differential Diagnosis

This post is derived from notes I took during training. Any images are copyright their respective owners.

Focal nodular hyperplasia (FNH)
  • Demographics: young women 
  • Pathology: localized hyperplastic hepatocyte response to an underlying congenital arteriovenous malformation 
  • MR: fibrous central scar that is T2↑, T1↓ with delayed, enhancing scar 
  • US: internal vascularity in spoke wheel configuration 
  • NM: Uptake ↑ on sulfur colloid scan due to Kupffer cell uptake. HIDA positive. 
  • Differential: Adenoma (photopenic on sulfur colloid)

Hepatic adenoma
  • Demographics: Young women on contraceptives
  • MR: mixture of fat, hemorrhage, necrosis; fat will be T1 bright, drops out on opposed phase imaging; may see internal vascularity / hyperintense capsule; if bleeding, may see hematoma as below 
  • Management: Monitor for size; if greater than 4 cm, treat because of bleeding risk

Hepatic hemangioma

  • Most common benign liver mass, not prone to spontaneous bleeding 
  • US: Homogeneously echogenic with no flow on Doppler. Never see hypoechoic halo. 
  • CT/MR: typically early discontinuous nodular filling, fills centripetally
    if cavernous/large, may have central hypointense scar +/- calcification 
  • NM: delayed blood pool activity on Tc99m RBC has nearly 100% PPV

Hepatocellular carcinoma (HCC)
  • Demographics: older pts 
  • Pathology: associated with cirrhosis; MC primary hepatic malignancy. AFP elevated. 
  • MRI: hypointense but with rapid uptake and early washout. Portal vein invasion. 
  • Differential: regenerative nodules (not hypervascular, no PV invasion), regenerative nodular hyperplasia (associated with Budd-Chiari, resemble FNH) 
  • Treatment: Chemo, Ablation, Surgery 
Fibrolamellar HCC
  • Demographics: young adults, may have h/o hepatitis 
  • CT/MRI: Large, calcified central scar; heterogeneous appearance 
  • Differential: FNH (smaller, older patients, more homogeneous appearance, enhancing scar)

  • Children: Neuroblastoma (Stage 4 & 4S), Burkitt, Wilms, AML, Sarcomas 
  • Adults: 
    • Hyperechoic: Colon, RCC, Breast (either), Carcinoid, Chorio 
    • Hypoechoic: Breast (either), pancreas, lung, lymphoma 
    • Calcified: colon (mucinous type), gastric, osteosarcoma (rare) 
    • Cystic: ovarian cystadenoca, GI sarcoma 
    • US: hypoechoic rim (target sign)



Tuesday, December 18, 2018

How To Read A Shoulder MRI

Shoulder MRI is a common musculoskeletal imaging exam. The exam is typically ordered for shoulder pain with suspicion of underlying rotator cuff pathology. Contrast is not needed. If there is a concern for labral pathology, an MRI arthrogram may be ordered. The arthrogram requires gadolinium-based contrast to be injected intra-articularly under fluoroscopic guidance prior to the MRI. The steps below are for a routine, non-contrast MRI.

The MRI shoulder is usually acquired in 3 planes (axial, sagittal, and coronal) obliqued to the plane of the scapula. Usually each plane is acquired as PD and T2, with one of the planes being done as a T1 instead of PD.

Prior to looking at the MRI, it is helpful to compare with any prior shoulder x-rays available.

On the MRI, the assessment should include:
  • Long heads of the biceps tendon: Start on the axial sequences and follow it along its course in the bicipital group to its origin at the biceps labral anchor
  • Supraspinatus (SS)
  • Infraspinatus (IS)
  • Teres Minor
  • Subscapularis (SSc)
  • Rotator Interval [2]
  • Labrum: best seen on the axial and coronal sequences; should appear hypointense and symmetric. Better assessed on MR arthrogram. 
  • Coracohumeral ligament (CHL): best seen on the coronals as a hypointense structure arising from the lateral coracoid, with its medial band inserting on the lesser tuberosity, and lateral band, greater tuberosity
  • Inferior glenohumeral ligament (IGHL): also assessed on the coronal
  • Acromioclavicular joint
  • Humerus and other bony structures
  • Spinoglenoid notch
  • Suprascapular notch
  • Quadrilateral space

Shoulder MRI Pearls:
  • Fluid in the subcoracoid bursa is suggestive of a tear [1]
  • Articular side anterosuperior rotator cuff tears (ie SSc and SS tears) can dissect into the CHL
  • IGHL is greater than 4 mm in capsulitis, but this should be a clinical diagnosis ultimately

This post is derived from notes I took during training. Any images are copyright their respective owners.

Revised: 2019-01-25