Showing posts with label Variation. Show all posts
Showing posts with label Variation. Show all posts

August 21, 2014

Renal Artery Variants in Patients with Normal Renal Function


3D volume rendered CT image shows a 2nd right renal artery (arrows) arising from the right common iliac artery

Facts

  • "Normal" renal arterial arrangement = single bilateral renal arteries with hilar segmental branching. This occurred in 46% of cases in a landmark angiographic report published in 1978
  • Normally, no intrarenal arterial anastomoses are present. Each artery represents an end artery -- interruption results in infarction of that segment
  • Variations include double renal arteries, triple renal arteries, pre-hilar segmental branching, fetal lobulation and exaggerated size difference (greater than 2 cm). 
  • Most common variations are multiple renal arteries followed by pre-hilar segmental branching


Knowledge of Renal Vascular Variations is Important For:

  • Renal transplantation
  • Renovascular hypertension
  • Vascular reconstruction for congenital and acquired lesions
  • Reconstructive surgery for abdominal aortic aneurysms
Our case: Double right renal artery with the smaller branch originating from the common iliac artery

Reference:
- Harrison, Jr., et al. Incidence of anatomical variants in renal vasculature in the presence of normal renal function. Ann Surg 1978;188:83-89.
- Ozkan U, et al. Renal artery origins and variations: angiographic evaluation of 855 consecutive patients. Diagn Interv Radiol 2006;12:183-6.

August 1, 2014

Vertebral Artery Hypoplasia

Curved reformat of the normal-caliber right vertebral artery showing all 4 segments of the artery. 
Curved reformat of the left vertebral artery shows diffuse, small caliber of the artery.

Facts:

  • Operational definitions are either 1) asymmetrical ratio of or greater than 1:1.7, or 2) discrepancy of greater than 2 mm diameter
  • Prevalence 2%-6% of population (from autopsy and angiographic series)
Clinical Relevance
  • Posterior circulation ischemia: hypoplasia leads to reduction of posterior circulation blood flow velocity therefore has a negative role in occlusion of major cerebral arteries
  • Migraine with aura and vestibular neuronitis: hypoplasia is believed to be associated with regional hypo perfusion and complex neurovascular consequences

Reference:
Chuang YM, Chan L, Wu HM, et al. The clinical relevance of vertebral artery hypoplasia. Acta Neurol Taiwan 2012;21:1-7.

May 1, 2013

Pancreatic Divisum

An MRCP image shows abnormal drainage of the main pancreatic duct and ventral duct into the minor papilla.

A diagram shows normal pattern of pancreatic duct drainage (label "normal") and pancreatic divisum. Several variants of pancreatic divisum exist but the "classic/typical" one is the MPD draining into the minor papilla while the VD draining into the major papilla along with the CBD. Santorinicele is a fusiform dilatation of the distal MPD before it enters the minor papilla. 

Facts: Pancreatic Divisum 

  • Most common pancreatic anatomic variant, found 7% incidence at autopsy but frequencies differ at ERCP
  • Controversial association with recurrent pancreatitis
  • Results of non-fusion of ventral and dorsal pancreatic anlagen during embryonic time, therefore the ducts (ventral and dorsal ducts are not fused)
  • Dorsal duct drains most of glandular parenchyma through minor papilla
  • Ventral duct drains a portion of pancreatic head (including uncinate process) through major papilla
Imaging:
  • Definitive diagnosis is made with ERCP. MRCP does have high sensitivity and specificity for diagnosis of divisum
  • MDCT with thin section can be used to diagnose pancreatic divisum. Viewing images on PACS is essential for depiction of this condition and the assessment is possible only when the pancreatic duct is visualized.
  • Important criterion = Dorsal duct seen from tail and body through the anterior aspect of the head, draining into minor papilla (located anterior to CBD and major papilla) while the ventral duct seen in posterior region of the pancreatic head and drains into duodenum together with CBD. Dorsal duct is larger than ventral duct and they are not communicated with each other. "Dominant dorsal duct sign"

Reference:
Soto JA, Lucey BC, Stuhlfaut JW. Pancreas divisum: depiction with multi-detector row CT. Radiology 2005; 235:503-508. 

November 15, 2009

Os Terminale - Os Odontoideum Complex (3)

A sagittal-reformated CT image shows a characteristic appearance of os odontoideum (O). Note a wide gap between the os and the hypoplastic dens (D). The anterior arch of C1 (A) is hypertrophied.


Facts: Os Odontoideum
  • Ossicle either in a normal odontoid tip (orthotopic) or near basi-occiput (dystrophic)
  • Often fixed to the anterior C1 ring and the two move as a single unit
  • Often asymptomatic (found incidentally) but some patients may have symptoms of C1-2 instability or at risk of developing cord injury following severe trauma
Imaging Features
  • Smooth, small or large ossicle, can be rounded or oval or very bizarre and irregular in shape
  • Hypoplastic dens. Wide gap between the os and dens
  • Anterior arch of C1 is hypertrophied
  • Jigsaw sign (a narrow joint space between the anterior C1 arch and the os, and an interdigitating joint line)
Differentiation of Unstable Os Odontoideum from Ununited Dens Fracture
  • In ununited dens fracture, the dens is normal in size and configuration but there is nonunion through the base of the dens. Nonunited fragment becomes hypermobile and behave like an os odontoideum. However, either of this would need surgical stabilization
Clinical Implication
  • The whole complex is variably unstable; therefore superimposed cervical spine trauma can make it more unstable and even can lead to acute cord injury
  • Suggest instability if 1) forward flexion of C1 on C2 more than 2 mm on flexion view, or 2) the os is posterior to its normal location
References:
1. Fagan AB, Askin GN, Earwaker JWS. The jigsaw sign. A reliable indicator of congenital aetiology in os odontoideum. Eur Spine J 2004;13:295-300.
2. Truumees E. Os odontoideum. E-medicine, updated September 12, 2008.
3. Swischuk L. Imaging of cervical spine in children, 2004.

November 12, 2009

Os Terminale - Os Odontoideum Complex (2)

Sagittal reformatted CT image shows an os terminale, sitting on top of the normal-sized dens.


Os Terminale
  • Derived from the 4th occipital sclerotome but does not undergo fusion with the dens
  • The dens is normal in size and shape
  • If it enlarges, coupled with dens hypoplasia -- it is called os odontoideum
  • Usually single, smooth
  • Sometimes can show bony fragmentation mimicking a comminuted fracture (but one should be aware that an extensively comminuted fracture at the tip of the dens is extremely rare or nonexistent)
Reference:
Swischuk L. Imaging of the cervical spine in children, 2004.

November 9, 2009

Os Terminale - Os Odontoideum Complex (1)

Diagram showing a range of dens anomalies from normal, os terminale and os odontoideum (hypoplastic dens). Adapted from Reference #1.


"I have always considered them [os terminale and os odontoideum] to be the same, believing that the os terminale becomes the os odontoideum when it enlarges in association with hypoplasia of the dens." - Leonard Swischuk, MD

Development of os terminale/os odontoideum complex
  • Os terminale is derived from the 4th occipital sclerotome
  • Os terminale develops and then fuses with the dens in most cases (becoming the tip of the dens)
  • If the os terminale does not fuse with the dens, it can overgrow and become the os odontoideum while the dens becomes hypoplasia. At the same time C1-2 stabilizing ligaments will be underdeveloped and predispose this section to hypermobility and instability
Imaging Appearance
  • Both os terminale and os odontoideum typically is a single, smooth ossicle
  • Sometimes, they can show bony fragmentation, bizarre and irregular in shape
  • If found posterior to its normal location, one can presume that there is some degree of instability
  • Anterior arch of C1 can overgrow (hyperplastic); this does not suggest that there is ununited fracture of the dens
Reference:
1. Swischuk L. Imaging of the cervical spine in children, 2004.

August 9, 2009

Azygos Fissure



Azygos Fissure
  • Normal variant, found in 1% of anatomic specimen and about 0.4% of chest radiographs
  • Right posterior cardinal vein (precursor of azygos vein) fails to migrate over lung apex, instead penetrating the lung and carrying pleural layers with it.
  • Two folds of parietal and visceral pleural layers create a "fissure"
  • Enclosed lung is a part of apical or posterior segment of the right upper lobe

Findings
  • Fine, convex line crosses the apex of the right lung.
  • Azygos vein visible in the lowermost portion of the fissure "teardrop" shape.
  • Absence of azygos vein at the right tracheobronchial angle.

Mimics of Azygos Fissure
  • Scars
  • Walls of bullae
  • Displaced fissures
  • Supernumerary fissures

Reference:
Mata J, Caceres J, Alegret X, Coscojuela P, De Marcos JA. Imaging of the azygos lobe: normal anatomy and variations. AJR 1991;156:931-937.

June 9, 2009

Persistent Left Superior Vena Cava (SVC)

Fig. 1: Portable chest radiograph shows a right PICC line coursing from the right arm to the left side of the mediastinum (arrows).
Fig. 2: Coronal chest CT image performed with injection of the right antecubital vein shows dense contrast in the right axillary, subclavian, left brachiocephalic vein to the left SVC (arrowheads). There is no right SVC.


Persistent Left SVC
  • Persistence of left anterior cardinal vein
  • 0.3% of normal population; 4.4% in patients with congenital heart disease
  • In most cases, the right SVC is also present (82% - 90%) (i.e. double SVC)
  • Left SVC courses lateral to the aortic arch, main pulmonary artery, anterior to the left hilum and typically enters the coronary sinus that drains into the right atrium
  • In some cases, left SVC enters the left atrium. Left SVC draining into the left atrium is highly associated with intracardiac defects (commonly ASD)
Significance of left SVC
  • Need to know before performing SVC-pulmonary artery anastomosis
  • Need to know before performing open heart operation
Reference:

1. Shumacker HB, King H, Waldhausen JA. The persistent left superior vena cava. Surgical implications, with special reference to caval drainage into the left atrium. Ann Surg 1967;165:797-805.

2. Webb WR, Gamsu G, Speckman JM, et al. Computed tomographic demonstration of mediastinal venous anomalies. AJR 1982;139:157-161.

June 21, 2008

Hepatic angiography: Accessory Left Gastric Artery


รูปที่ 1 Celiac angiography แสดงให้เห็น branches ของ celiac trunk ได้แก่ (1) splenic artery,(2) common hepatic artery และ (3) left gastric artery

รูปที่ 2 แสดงให้เห็นถึง branches ที่ไปเลี้ยง stomach ได้แก่ (1) Left gastric artery, (2) Right gastric artery ซึ่งทั้งสองเส้นนี้เลี้ยงบริเวณ lesser curvature ของ stomach ส่วน  greater curvature นั้นจะเลี้ยงด้วย (3) Right gastroepiploic artery และ Left gastric epiploic artery (มองไม่เห็นจากรูปนี้) ส่วนบริเวณ fundus นั้นได้เลือดมาจาก (4) Short gastric artery และ (1) Left gastric artery


รูปที่ 3 Common hepatic angiography (A) ในช่วง late arterial phase แสดง (1) Left hepatic artery และ (2) Right hepatic artery. (B) ในช่วง portovenous phase จะเห็นว่ามี   contrast blush อยู่บริเวณ ลูกศรสีน้ำเงิน 


รูปที่ 4 Superselective left hepatic angiography ในรูป A จะเห็น left hepatic branches ที่ไปเลี้ยง   hepatic segment 2, 3 และ 4 ส่วนในรูป B นั้น จะเห็นว่า branch ดังกล่าวมีให้ลักษณะของ branching pattern ของ gastric fundus สรุปคือ branch นี้คือ accessory left gastric artery

Accessory left gastric artery

  •  พบในการตรวจ angiography ประมาณ 3-14% 
  • เลี้ยงบริเวณ cardia และ fundus ของกระเพาะอาหาร
  • วิ่งอยู่ใน fissure of ligamentum venosum
  • อาจแปลผลผิดว่าเป็นเส้นเลือดที่ไปเลี้ยงตับได้
  • มีความสำคัญในการทำ transarterial chemoembolization (TACE) ถ้าไม่สังเกตพบเสียก่อน อาจทำให้เกิด  complication ได้ เช่น เกิดแผลในกระเพาะอาหาร หรือผู้ป่วยมีคลื่นใส้ อาเจียนระหว่าง TACE ได้ 
Reference: 
  1. Ishigami K, Yoshimitsu K, Irie H, Tajima T, Asayama Y, Hirakawa M, Honda H.Accessory left gastric artery from left hepatic artery shown on MDCT and conventional angiography: correlation with CT hepatic arteriography. AJR Am J Roentgenol. 2006 Oct;187(4):1002-9.
  2. Lee KH, Sung KB, Lee DY, Park SJ, Kim KW, Yu JS.Transcatheter arterial chemoembolization for hepatocellular carcinoma: anatomic and hemodynamic considerations in the hepatic artery and portal vein.Radiographics. 2002 Sep-Oct;22(5):1077-91. 

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