Sabtu, 15 Januari 2011

Lymphatic System, Radiological Anatomy Notes

Lymphatic System, Radiological Anatomy Notes

CT:
  • Advantage
    • non-invasive
    • minimal expertise
    • easily reproducible for follow up
    • can image all intra-abdominal lymph nodes and extranodal disease
    •  
  • Disadvantage
    • Expensive
    • cant detect disease in normal sized vessels
    • cant detect vessel abnormalities or internal structure of lymph nodes
    • not seen retroperitonial fat 
US
  • Advantage
    • non-invasive
    • can image extranodal disease
  • Disadvantage
    • Operator dependent
    • bowel gas
    • Internal structure of lymph node not seen
    • Lymph node must be greater than 1,5cm to be seen
MRI
  • Advantage
    • Not specifically used to study the lymphatic system
    • Lymph nodes are well seen on MRI if pathological and enlarged
    • Tumour invasion and inflammatory changes - High T2 signal
    • Multiplanar - ability allows for accurate anatomical localisation
    • useful to characterise extent of tumour

CONSENSUS: PERFORM CT AT OUTSET - REVERSE LYPHOGRAPHY IS A SECOND LINE WHERE CT IS EQUIVOCAL OR NON-DIAGNOSTIC QUALITY


Imaging:

  • Plain films
  • Lymphangiography 
    • Lymphangiogram
    • Indications 
      • Suspect lymph vessel disease (lymphoedema) usually technically very difficult
      • Diseases effecting lymph nodes
        • Lymphomas and cancer that metastasis to retroperitoneum - ie cancer of the bladder and gonads
        • occult lymphoma associated with skin disorders
          • Mycosis fungoides, exfoliative dermatitis
      • Miscellaneous
        • Chyluria, chylothorax, lymphoceel, filiarisis
    • Contraindications
      • Pulmonary disease and poor lung function. 
        • pulmonary reaction to oily contrast media, risk of pulmonary emboli
      • Cardiovascular disease - IHD, CCF, and Right to Left Shunt
      • Radiotherapy to the lungs within 2 weeks 
        • dilatation of pulmonary capillaries and risk of paradox Pulmonary Emboli
      • Proposed GA
        • risk of GA is increased post lymphangiogram
      • Known hypersensitivity 
      • Sepsis and gross edema 
  • Contrast Media:
    • Oily
      • is the best contrast media - opacifies the nodes and vessels. Stays in Lymph nodes for months or years
    • H2O Soluble
      • opacifies only vessels - diffuse quickly into blood at 1st lymph node - only used for proximal afferent vessels.
  • Patient preperation
    • Sedation especially for children
    • if legs - elevate for 24 hours preprocedure
    • fasting patient and empty bladder
    • preliminary films - 
      • PA chest evaluation
      • Heart disorders - control abdominal xray
  • Technique for Bipedal Lymphography
    • Principle: a diffusible dye is injected subcutaneously so that it can be taken up by Lymph Vessels and colour them - and able to cannulate
    •  method used where there is a lymphatic drainage system, but vast majority - 
      • feet
      • hands - to a lesser extent
  1. Outlining of Lymphatics: Patient supine on Xray table, skin prep with hibitane. Patent blue dye mixed with local anaesthetic is injected interdigitally. Patient walks for 20 to 30 minutes and dye layden lymph vessels will be recognised as green vessels through the skin.
  2. Cannulation: small incision.
    1.  Lymphatic vessel is prepared and cannulated with a 26G needle borded to a polyethene cannula which is connected to a syringe and filled with saline. The best test for proper positioning is however, injection of contrast. Patient feels pain in the limb, usually mild, and eventual leaking of contrast can be demonstrated. 
    2.  
  3. Injection of contrast:
    1. usual dose of Lipoidol is 7 to 8 ml / foot
  4. Close incision
  5. Take Radiographs:
    1. Lymphatic phase
      1. AP pelvis
      2. Abdominal AP lat and oblique
      3. PA chest
        1. wait gently for 10 minutes them penetrate view to show thoracic duct
    2. nodal phase
      1. after 24 hours
      2. some people do IV Pat same time
    3. delayed phase - can asses response to treatment
      1. Supine abdominal
      2. AP pelvis
  6. Complications:
    1. D/T patent blue - 
      1. allergy is rare
      2. patient urine will be blue green for 24 hours
    2. D/T oily contrast media
      1. allergic reaction is rare
      2. pain during injection
      3. pulmonary air embolism
        1. minute high density opacities can be detected
        2. usually asymptomatic but fever and cough
      4. lymphangitis
      5. paradoxal embolus
      6. hepatic emboli
        1. lymph obstruction
    3. D/T technique
      1. extravasation 
      2. lymphatic rapture
      3. wound sepsis
  7. Findings
    1. Normal Lymphatic Vessels
      1. delicate linear channels < 1mm with beaded appearance above small valves that prevent retrograde flow
      2. ascend in straight lines without tortuousity
      3. tend to divide and rejoin
      4. efferent vessels leave via hilium of node - larger and fewer then afferent and more beaded
    2. Normal Lymph Nodes
      1. typically ovoid and 1,5 cm to 2 cm 
      2. each node is outlined by its marginal sinus
      3. closely packed punctate pattern of contrast and contain defects d/t lymphoid follicles in the node(characterized by dots or points)
    3. The Thoracic duct
      1. Extends from the Cisterna Chyli and runs through the aortic hiatus and in thorax lies between aorta and azygos vein
      2.  http://radiographics.rsna.org/content/24/3/809/F1.expansion
      3. Joins junction of Left subclavian and Left jugular veins
      4. The Duct is beaded by its velves and has variable width upto 8 mm in some cases
      5. Often slightly dilated just before its venous junction 
      6.  
  8. Advantages of Lymphangiography
    1. only direct radiological approach to visualise lymph nodes and vessels
    2. only method to study lymphatic vessels and its disorders
    3. May detect disease in normal sized lymph nodes
    4. can asses internal structure of lymph nodes
  9. Disadvantages
    1. Technically difficult 
    2. Time consuming
    3. Maybe medically contraindicated
    4. Does not image liver and spleen
      1. Lymph nodes: internal iliac, mesenteric, retrocrural, hilar

Guermazi A, Brice P, Hennequin C, Sarfati E (2003). "Lymphography: an old technique retains its usefulness". Radiographics 23 (6): 1541–58; discussion 1559–60. doi:10.1148/rg.236035704.PMID 14615563. Full text



  1. paradoxal embolus
    1. A paradoxical embolism is a kind of stroke or other form of arterial thrombosis caused by embolism of a thrombus (blood clot) of venous origin through a lateral opening in the heart, such as a patent foramen ovale.[1]
      The opening is typically an atrial septal defect, but can also be a ventricular septal defect.
      Paradoxical embolisms represent two percent of arterial emboli.[2]

      Pathophysiology

      Passage of a clot (thrombus) from a vein to an artery. When clots in veins break off (embolize) , they travel first to the right side of the heart and, normally, then to the lungs where they lodge, causingpulmonary embolism. On the other hand, when there is a hole in the wall between the two upper chambers of the heart (an atrial septal defect), a clot can cross from the right to the left side of the heart, then pass into the arteries as a paradoxical embolism. Once in the arterial circulation, a clot can travel to the brain, block a vessel there, and cause a stroke (cerebrovascular accident). Also called crossed embolism.

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