Sunday, February 28, 2010

The nuchal ligament

The nuchal "ligament" (ligamentum nuchae) composed of two parts: the dorsal raphe and the midline fascial septum. In humans, neither component is a true ligament, leading some to question the terminology. The image shows a patient with a disrupted dorsal raphe following trauma.

The dorsal raphe, also known as the funicular (funiculus: Latin for rope) portion of the nuchal ligament, extends from the external occipital protuberance to the spinous process C7. The dorsal raphe is not a true ligament. It is formed by interlacing tendons of the trapezius muscle throughout the course of the dorsal raphe and by the fibers of the splenius capitis and rhomboid minor muscles caudad to the C4 spinous process.

The second part of the nuchal "ligament" is the midline fascial septum (also known as the lamellar portion) is attached to the ventral aspect of the dorsal raphe and extends to the tips of the spinous processes. Rostrally, it attaches to the external occipital protuberance and the external occipital crest.

It has been suggested by some that preserving the dorsal raphe at C6 and C7 during laminoplasty can prevent undesirable radiologic changes such as kyphotic deformity and destabilization.

Calcifications can be seen along the nuchal "ligament" and are thought to represent sesamoid bones.

Trivia

The nuchal ligament in quadrupeds is a true ligament that supports the dependent head. It is known as the paxwax (bastardization of faxwax which is Old English for hair and to grow). Paxwax itself has been bastardized as paddywhack or paddywack, and can be found in the nursery rhyme, "This old man." Today, paxwax is commonly sold in pet stores as a doggie treat.

References

  • Kadri PA, Al-Mefty O. Anatomy of the nuchal ligament and its surgical applications. Neurosurgery. 2007 Nov;61(5 Suppl 2):301-4;
  • Mercer SR, Bogduk N. Clinical anatomy of ligamentum nuchae. Clin Anat. 2003 Nov;16(6):484-93.
  • Sakaura H, Hosono N, Mukai Y, Oshima K, Iwasaki M, Yoshikawa H. Preservation of the nuchal ligament plays an important role in preventing unfavorable radiologic changes after laminoplasty. J Spinal Disord Tech. 2008 Jul;21(5):338-43.
  • Scapinelli R. Sesamoid bones in the ligemntum nuchae of man. J Anat. 1963 Jul;97:417-22.

Saturday, February 27, 2010

Mesenteric Panniculitis

Mesenteric panniculitis is chronic inflammation of the mesenteric fat. The etiology of mesenteric panniculitis is unclear, but it has been linked to vasculitis, granulomatous disease, rheumatic disease, malignancy, and pancreatitis.

Mesenteric panniculitis may be complicated by fibrosis and retraction, at which point it is referred to as mesenteric fibrosis.

CT findings of mesenteric panniculitis include:
  • A well-circumscribed heterogeneous fatty mass: Usually extends from the mesenteric root towards the jejunum. A high-attenuation stripe may partially surround the mass (tumoral pseudocapsule).
  • Higher attenuation of the involved fat: Also known as segmental misty mesentery
  • Well-defined nodules: Soft-tissue density nodules less than 5 mm in diameter. May have a low-attenuation halo.
  • Fat ring sign: Preservation of the low fat attenuation surrounding mesenteric vessels.
Patients may present with progressive or intermittent symptoms, including a palpable abdominal mass, as well as systemic manifestations such as abdominal pain, pyrexia, weight loss, and bowel disturbance

References

Friday, February 26, 2010

The Garden Classification

The Garden classification of femoral neck (subcapital) fractures is the most commonly used system and is based on the degree of displacement on the anteroposterior radiographs.
  • Stage I: Incomplete fracture (impacted valgus fracture).
  • Stage II: Complete fracture with minimal or no displacement from anatomically normal position.
  • Stage III: Complete fracture with partial displacement.
  • Stage IV: Complete fracture with full displacement.
Differentiation between nondisplaced (Garden I and II) and displaced (Garden III and IV) femoral neck fractures has therapeutic as well as prognostic value. Type I and II fractures have a low incidence of avscular necrosis and are usually treated by internal fixation using a dynamic hip screw. The high incidence of avascular necrosis in type III and IV fractures precludes internal fixation, and these fractures are often treated by arthroplasty.

References

  • Garden R. Low-angle fixation in fractures of the femoral neck. J Bone Joint Surg Br, 1961(43):647–661.
  • Zlowodzki M, Bhandari M, Keel M, Hanson BP, Schemitsch E. Perception of Garden's classification for femoral neck fractures: an international survey of 298 orthopaedic trauma surgeons. Arch Orthop Trauma Surg. 2005 Sep;125(7):503-5.

Thursday, February 25, 2010

Arcuate Foramen

The arcuate foramen is formed by a bony bridge (ponticulus posticus, or little posterior bridge) over a groove in the posterolateral margin of C1 known as the sulcus arteriae vertebralis. The vertebral artery and first cervical nerve normally travel within the sulcus arteriae vertebralis, and, when the ponticulus posticus is present, through the arcuate foramen.

The arcuate foramen is also known as as Kimmerle anomaly, foramen sagittale, foramen atlantoideum, foramen retroarticulare superior, and canalis vertebralis. It has been suggested that the ponticulus posticus comes about through ossification of the oblique portion of the atlantooccipital ligament, while others have found no age-difference to suggest an acquired process.

References

Wednesday, February 24, 2010

Appearance of the Paranasal Sinuses in Acromegaly

The paranasal sinuses and mastoid air cells in patients with acromegaly are typically enlarged. In addition, the bones of the calvarium are thickened and hyperostosis frontalis interna is common. The pituitary fossa may be normal or enlarged.

References

Price HI, Batnitzky S, Karlin CA, Gilmore RL. Computed tomography of benign disease of the paranasal sinuses. Radiographics 1983 3:107-140.

Tuesday, February 23, 2010

Posterior Vertebral Scalloping

The mnemonic AMEN can be used to remember the differential diagnosis for the appearance of scalloped posterior vertebral bodies.
  • Acromegaly: Caused by soft tissue hypertrophy and bone resorption
  • Achondroplasia: Caused by a small spinal canal. May also see caudal narrowing of the spinal canal.
  • Ankylosing spondylitis: Caused by dural ectasia
  • Marfan syndrome: Caused by dural ectasia
  • Mucopolysaccharidoses (Morquio disease and Hurler syndrome): May also see platyspondyly and anterior vertebral body beaks.
  • Ehlers-Danlos syndrome: Caused by dural ectasia
  • Neurofibromatosis: Caused by dural ectasia. May also see scoliosis and syringomyelia
Hydrocephalus and intraspinal tumors may also cause scalloping via increased intraspinal pressures, but they don't fit in the mnemonic.

References

Wakely SL. The posterior vertebral scalloping sign. Radiology. 2006 May;239(2):607-9.

Monday, February 22, 2010

The Semisupinated Oblique View of the Wrist

The semisupinated oblique view of the wrist is an oblique view obtained by resting the back of the hand on a 45-degree wedge.

This view shows the dorsal cortex of the radius without the overlap from the ulna seen on the lateral view. This view also highlights the pisiform bone and the pisotriquetral joint, and allows for visualization of loose bodies in the superior and inferior recesses of the pisotriquetral joint. The palmar portion of the hook of the hamate is also well seen on this view.

References

Sunday, February 21, 2010

Normal Enhancement of the Facial Nerve

The circumferential facial arteriovenous plexus provides arterial supply and venous drainage of the facial nerve, the ossicular chain, the middle ear muscles and tendons, and of the mucosa and bone walls of the tympanic cavity. The plexus is suspected to result in non-pathological apparent enhancement of at least one segment of the normal facial nerve in about 75% of cases.

The segments that most commonly show normal apparent enhancement are the mastoid segment (100%) the geniculate ganglion (78%) and the tympanic segment (38%). The intracanalicular (meatal) and labyrinthine segments can also show mild apparent enhancement in some cases (15% and 5%, respectively); however, intense enhancement of these two segments is characteristically seen in Bell palsy.

References

  • Gebarski SS, Telian SA, Niparko JK. Enhancement along the normal facial nerve in the facial canal: MR imaging and anatomic correlation. Radiology. 1992 May;183(2):391-4.
  • Hong HS, Yi BH, Cha JG, Park SJ, Kim DH, Lee HK, Lee JD. Enhancement pattern of the normal facial nerve at 3.0 T temporal MRI. Br J Radiol. 2010 Feb;83(986):118-21.

Saturday, February 20, 2010

Tracheoinnominate Artery Fistula

Tracheoinnominate artery fistula, or simply tracheoinnominate fistula, may be caused by pressure necrosis from high cuff pressure, mucosal trauma from malpositioned cannula tip, low tracheal incision, excessive neck movement, radiotherapy, and prolonged intubation.

Reports on imaging are few (at least those available electronically) and seem restricted to angiography. Normal diagnostic aortograms have been reported and should not delay treatment. Selective catheterization of the innominate artery and careful evaluation may reveal the site of the lesion.

References

Cohen JE, Klimov A, Rajz G, Paldor I, Spektor S. Exsanguinating tracheoinnominate artery fistula repaired with endovascular stent-graft. Surg Neurol. 2008 Mar;69(3):306-9.

Friday, February 19, 2010

The Radial Head—Capitulum View

The radial head-capitulum view is a modified lateral view of the elbow that is obtained by angling the tube 45 degrees toward the radial head. This results in projection of the radial head ventrally and eliminates overlap of other bones. The radial head-capitulum view also separates the humeroradial and humenoulnar articulations.

Practically speaking, there are several ways of obtaining the view, nicely reviewed and illustrated by Hobbs (2005):
  • Sitting Axial Lateromedial Projection (Coyle Method): The patient is seated on a chair at the end of the examination table with the elbow flexed at about 90° (exact 90° flexion is not necessary) and the palm facing the film and table top. The x-ray tube is angled 45° in a lateromedial projection with the central ray directed to the mid-elbow joint.
  • Recumbent axial lateromedial projection (Coyle Method): The elbow is flexed at about 90° (exact 90° flexion is not necessary) with the palm facing the film. The x-ray tube is angled 45° in a lateromedial projection with the central ray directed to the mid-elbow joint.
  • Sitting 45° axial mediolateral projection: The patient is seated on a chair at the end of the examination table with the dorsal side of the forearm facing the film. The arm is brought slightly forward so that the elbow is at an angle of greater than 90°. The tube is directed at a 45° mediolateral projection with the central ray directed to the mid-elbow joint. This is a good projection in that it can be performed on a patient in an arm sling. In addition, by obtaining a 45° lateromedial projection in the same position, we can get a good look at the coronoid process.

References

  • Greenspan A, Norman A. The radial head, capitellum view: useful technique in elbow trauma. AJR Am J Roentgenol. 1982 Jun;138(6):1186-8.
  • Greenspan A, Norman A, Rosen H. Radial head-capitellum view in elbow trauma: clinical application and radiographic-anatomic correlation. AJR Am J Roentgenol. 1984 Aug;143(2):355-9.
  • Hobbs DL. Fat pad signs in elbow trauma. Radiol Technol. 2005 Nov-Dec;77(2):93-6.

Thursday, February 18, 2010

Limbic Encephalitis

Limbic encephalitis, also known as paraneoplastic encephalitis, refers to the subacute (weeks) development of severe memory loss and behavioral abnormalities, and may be accompanied mood alteration, delusions, and seizures.

Limbic encephalitis is almost always associated with an underlying malignancy, most commonly small cell carcinoma of the lung, but association with autoimmune disorders such as lupus has also been reported.

Imaging findings predominate in one or both temporal lobes. CT may show low attenuation areas in the temporal lobes. In the acute phase, MRI may show T2/FLAIR hyperintensity in the temporal lobes, while FDG/PET may show increased uptake. Contrast-enhanced MRI may show Patchy enhancement. Decreased FDG uptake may be seen in the chronic phase.

Differential considerations for the imaging appearance include:
  • Herpes simplex encephalitis
  • Vasculitis
  • Low-grade astrocytoma (unilateral)
  • Status epilepticus
  • Gliomatosis cerebri
  • Metastases
  • Radiation therapy

References

  • Kano O, Arasaki K, Ikeda K, Aoyagi J, Shiraishi H, Motomura M, Iwasaki Y. Limbic encephalitis associated with systemic lupus erythematosus. Lupus. 2009 Dec;18(14):1316-9.
  • Ravin CE, Bergin D, Bisset GS 3rd, Fine SA, Guo AC, Helms CA, Hollingsworth CL, Kirk SR, Ravenel JG. Image interpretation session: 2000. Radiographics. 2001 Jan-Feb;21(1):267-87.

Wednesday, February 17, 2010

Alveolar Sarcoid

Alveolar sarcoid refers to an atypical presentation of pulmonary sarcoidosis. There are large opacities ranging in diameter from 1 cm to 4 cm with a rounded or elongated shape, irregular edges and blurred margins with or without air bronchograms. They are typically found in the parahilar or peripheral regions.

The opacities don't represent a true alveolar process, but result from the confluence of a large number of interstitial granulomas. Indeed, on CT, small nodules are often visible around these large opacities, an appearance that has been called the galaxy sign.

Another pattern of alveolar sarcoid is the so-called "fairy ring." This refers to circumferentially organized opacities. On mediastinal windows, this can mimic central necrosis, but lung windows reveal apparently normal lung centrally. It is hypothesized that the central area represents spontaneous resolution of granulomatous inflammation with new granulomatous inflammation developing peripherally.

References

Tuesday, February 16, 2010

Hippocampal Malrotation

Hippocampal malrotation, perhaps more properly referred to as incomplete hippocampal inversion, is the constellation of:
  • Incomplete inversion of the hippocampus with with an abnormally round shape
  • Unilateral involvement of the whole hippocampus: Most often left-sided
  • Normal hippocampal signal intensity and size
  • Blurred hippocampal internal structure
  • Abnormal angle of the collateral sulcus: The normal collateral sulcus angle is flat at the level of the body and tail of the hippocampus, and more vertical in cases of hippocampal malrotation
  • Abnormal position and size of the fornix: Normally symmetrical, the fornix may be inferiorly displaced in patients with hippocampal malrotation. However, a low fornix can also be seen in subjects without seizures and without hippocampal malrotation, suggesting that it may be an incidental finding.
  • Normal size of the temporal lobe.
  • Enlargement and particular configuration of the temporal horn seen with agenesis of the corpus callosum but with a normal corpus callosum.
The full constellation is reportedly not present in patients without seizures, while others have found no causality between temporal lobe epilepsy and hippocampal malrotation. Raininko and Bajic (2010) suggest that hippocampal malrotation is a common variant that can be a sign of disturbed cerebral development, which in turn may affect other parts of the brain, leading to epilepsy. Gamss et al (2009) suggest that like mesial temproal sclerosis, hippocampal malrotation is uncommon in people without seizures and should elevate suspicion for an underlying epileptogenic disorder.

References

  • Barsi P, Kenéz J, Solymosi D, Kulin A, Halász P, Rásonyi G, Janszky J, Kalóczkai A, Barcs G, Neuwirth M, Paraicz E, Siegler Z, Morvai M, Jerney J, Kassay M, Altmann A. Hippocampal malrotation with normal corpus callosum: a new entity? Neuroradiology. 2000 May;42(5):339-45.
  • Gamss RP, Slasky SE, Bello JA, Miller TS, Shinnar S. Prevalence of hippocampal malrotation in a population without seizures. AJNR Am J Neuroradiol. 2009 Sep;30(8):1571-3.
  • Raininko R, Bajic D. "Hippocampal Malrotation": No Real Malrotation and Not Rare. AJNR Am J Neuroradiol. 2010 Jan 14.

Monday, February 15, 2010

CT Angiography Spot Sign

The CTA spot sign is a focus of enhancement within acute intracranial hematomas that is associated with expansion of an acute hematoma. Expansion of hematoma is, in turn, associated with increased mortality and diminished functional outcomes.

Other risk factors for hematoma expansion include hyperglycemia,hypertension, and anticoagulation.

References

Wada R, Aviv RI, Fox AJ, Sahlas DJ, Gladstone DJ, Tomlinson G, Symons SP. CT angiography "spot sign" predicts hematoma expansion in acute intracerebral hemorrhage. Stroke. 2007 Apr;38(4):1257-62.

Sunday, February 14, 2010

Stenogyria

Stenogyria (stenos=narrow) refers to the packing of small gyri with shallow sulci and preservation of the general sulcal pattern. It is the most common cortical malformation described in Chiari II and is seen predominantly in the posterior and medial portion of the hemispheres.

On histological evaluation, stenogyric brain demonstrates normal cortical organization (in contrast to polymicrogyria). There is typically thinning of the underlying white matter.

References

Miller E, Widjaja E, Blaser S, Dennis M, Raybaud C. The old and the new: supratentorial MR findings in Chiari II malformation. Childs Nerv Syst. 2008 May;24(5):563-75.

Saturday, February 13, 2010

Lung Cancer Staging and Resectability

UPDATED based on the 7th edition of the Tumor, Node, and Metastasis (TNM) staging manual of non–small cell lung cancer.

Early-stage disease (stage I, II, and, in some cases, IIIA) is considered surgically resectable with or without neoadjuvant or adjuvant chemotherapy and radiation therapy.

Stage IIIB and IV tumors are considered unresectable. Under the 7th edition TNM classification, stage IIIB is defined as 1) T4, N2, M0 OR 2) T1-T4, N3, M0. Presence of M1 disease bumps the stage to IV.
  • T4: Tumor (size is irrelevant) that invades the mediastinum, trachea/carina, heart, great vessels, esophagus, or vertebral body.
  • N2: Ipsilateral mediastinal or subcarinal nodes.
  • N3: Contralateral hilar and mediastinal and contra- or ipsilateral scalene and supraclavicular nodes.
  • M1: Thoracic (M1a): Malignant pleural effusions, pleural dissemination, pericardial disease, and pulmonary nodules in the contralateral lung. Extrathoracic (M1b): Spread to locations away from the chest (liver, adrenal gland, brain, etc.).
In semi-plain English: 1) Any tumor size that involves contralateral, scalene, or supraclavicular nodes is unresectable, 2) T4 tumor is unresectable once nodes other than ipsilateral hilar are involved, and 3) Any metastatic disease is considered unresectable.

T4 tumor with ipsilateral hilar nodes (N1) is now considered stage IIIA and resectable.

Quick Links

References

UyBico SJ, Wu CC, Suh RD, Le NH, Brown K, Krishnam MS. Lung cancer staging essentials: the new TNM staging system and potential imaging pitfalls. Radiographics. 2010 Sep;30(5):1163-81.

Friday, February 12, 2010

Idiopathic giant bullous emphysema

Idiopathic giant bullous emphysema (vanishing lung syndrome, type 1 bullous disease, or primary bullous disease of the lung) is a progressive condition characterized by extensive paraseptal emphysema coalescing into giant bullae. It usually occurs in young men, most of whom are smokers, but can also occur in nonsmokers.

Radiographs will reveal giant bullae in one or both upper lobes that occupy at least one third of the hemithorax and compress surrounding normal lung parenchyma. On HRCT, multiple large bullae may be seen without a single dominant giant bulla. There may also be subtle parenchymal paraseptal and centrilobular emphysema in the apparently normal lung.

References

Stern EJ, Webb WR, Weinacker A, Müller NL. Idiopathic giant bullous emphysema (vanishing lung syndrome): imaging findings in nine patients. AJR Am J Roentgenol. 1994 Feb;162(2):279-82.

Thursday, February 11, 2010

Pulmonary Complications Following Bone Marrow Transplantation

The differential diagnosis for pulmonary complications following bone marrow transplantation can be narrowed based on timing. Chest radiography is the mainstay of radiologic evaluation, but HRCT can demonstrate a significant pulmonary abnormality in 10% of immunosuppressed patients with normal chest radiographs.

Time Infectious Non-infectious
Neutropenic
(<30 d)
Invasive aspergilosis, Candida Pulmonary edema, Drug reaction, DAH
Early
(30-100 d)
CMV, PCP Engraftment syndrome
Late
(>100 d)
Uncommon OB, COP, GVHD
CMV=cytomegalovirus, COP=cryptogenic organizing pneumonia, DAH=diffuse alveolar hemorrhage, GVHD=graft-versus-host disease, OB=obliterative bronchiolitis, PCP=Pneumocystis jirovecii pneumonia


During the neutropenic phase, non-infectious causes comprise between 50% to 80% of pulmonary complications. Pulmonary edema is seen in up to 65% of patients.

DAH is now uncommon, but has an associated mortality of up to 100%. Chest radiographs may reveal bilateral areas of predominantly perihilar and lower lung ground-glass and patchy consolidation. There is rapid deterioration.

The differential considerations change after engraftment. The return of neutrophils makes bacterial and fungal infection less common, and CMV and other viruses become the dominant pathogens. PCP is now less common due to availability of PCP prophylaxis.

Engraftment syndrome refers to diffuse alveolar damage following bone marrow transplantation in the absence of an infectious etiology. The chest radiographs may reveal bilateral pleural effusions, transient pulmonary infiltrates, and interstitial pulmonary edema.

Obliterative bronchiolitis (OB) is the most common noninfectious respiratory complication after hematopoietic stem cell transplantation, occurring in up to 20% of cases. Chest radiographs may reveal signs of hyperinflation, recurrent pneumothorax and occasional focal/diffuse opacities. There may be bronchial dilatation, bronchial wall thickening, peripheral vascular pruning and mosaic attenuation with air trapping on expiratory scans on HRCT.

References

TM, Moss HA, Robertson RJ, Barnard DL. Pulmonary complications following bone marrow transplantation. Br J Radiol. 2003 Jun;76(906):373-9.

Wednesday, February 10, 2010

Flat Waist Sign

Flat waist sign refers to the loss of concavity of the left heart border in left lower lobe atelectasis. Specifically, there is flattening of the contours of the aortic arch and main pulmonary artery on a symmetrical frontal chest radiograph due to slight right anterior oblique rotation of the heart.

References

Kattan KR, Wlot JF. Cardiac rotation in left lower lobe collapse. "The flat waist sign." Radiology. 1976 Feb;118(2):275-9.

Tuesday, February 9, 2010

Retrotracheal Triangle

The retrotracheal (RT) triangle, also known as the Raider triangle, is seen on the lateral chest radiograph and is bordered anteriorly by the posterior wall of the trachea, posteriorly by the upper thoracic vertebrae and inferiorly by the distal portion of the aortic arch. On frontal radiographs, the triangle is bordered superiorly by the thoracic inlet, laterally by the manubrial borders, and inferiorly by the aortic arch.

A number of processes may manifest as abnormalities of the Raider triangle, including:
  • Acquired vascular anomalies: Aortic aneurysm, pseudoaneurysm, transection.
  • Congenital vascular anomalies: Aberrant right subclavian artery (with left aortic arch), aberrant left subclavian artery (with a right aortic arch), double aortic arch.
  • Esophageal abnormalities: Esophageal atresia, Zenker diverticulum, achalasia, carcinoma.
  • Mediastinal masses: Neoplasm, hemorrhage, lymphadenopathy (shown above), lymphatic malformation, abscess.
  • Thyroid masses: Intrathoracic goiter.

References

Franquet T, Erasmus JJ, Giménez A, Rossi S, Prats R. The retrotracheal space: normal anatomic and pathologic appearances. Radiographics. 2002 Oct;22 Spec No:S231-46.

Monday, February 8, 2010

Myocardial Bridging

Myocardial bridging refers to an anatomic variant where a short segment of a coronary artery dips into and is completely surrounded by myocardium. As would be expected, this segment narrows during systole and re-expands during diastole. It is most commonly seen in the left anterior descending coronary artery.

Myocardial bridging is easily detected on conventional angiography, which reveals a characteristic "milking" appearance: The lumen of the arterial segment is compressed by myocardial contraction during systole but recovers its normal diameter in diastole.

On CT coronary angiography, however, myocardial bridging may be mistaken for focal stenosis. Multiplanar reformations help by depicting myocardial fibers overlying the arterial segment.

The bridged segment rarely has atherosclerosis, but plaques may be seen proximally and distally. Chest pain and myocardial infarction may occur if there is >75% narrowing during systole.

Septal perforating arteries, which are normally intramural, don't narrow much during systole unless there is increased left ventricular wall tension (e.g., as may be seen with aortic stenosis, hypertensive heart disease, and hypertrophic cardiomyopathy).

References

  • Choi HS, Choi BW, Choe KO, Choi D, Yoo KJ, Kim MI, Kim J. Pitfalls, artifacts, and remedies in multi- detector row CT coronary angiography. Radiographics. 2004 May-Jun;24(3):787-800.
  • Miller SW and Boxt LM. Chapter 7: Ischemic heart disease. in Cardiac Imaging: The Requisites (third ed). Miller SW et al (eds).

Sunday, February 7, 2010

Atrial Ridges

Crista Terminalis

The crista terminalis is a smooth muscular ridge within the right atrium that represents the line of fusion between the trabeculated primitive right atrium and the smooth-walled right atrium arising from the sinus venosus. It is oriented in the cradiocaudad direction and extends from the superior vena cava to the inferior vena cava.

It can often be seen extending into the right atrium. When prominent, it may be mistaken for a tumor or thrombus.

Warfarin (Coumadin) Ridge

The warfarin (Coumadin) ridge is a ridge of smooth muscle found along the wall of the left atrium at the junction of the left atrial appendage and the entrance of the left superior pulmonary vein. It derives its name from its misidentification as a thrombus and subsequent anticoagulation therapy with warfarin.

It may also be mistaken for a pedunculated mass arising from the lateral wall of the left atrium.

References

Broderick LS, Brooks GN, Kuhlman JE. Anatomic pitfalls of the heart and pericardium. Radiographics. 2005 Mar-Apr;25(2):441-53.

Saturday, February 6, 2010

Branches of the Coronary Arteries

  • Conus branch: The first branch of the right coronary artery (RCA) in about 50% of cases. Courses anteriorly to supply the right ventricular outflow tract. Can also arise from the left main coronary artery (LM) or have a common origin with the RCA.
  • Sinoatrial nodal artery (SAN): Usually the second branch of the RCA. Courses toward the superior vena cava inflow near the cephalad aspect of the interatrial septum. Can also arise from the proximal left circumflex coronary artery (LCx).
  • Acute marginal branches: Arise from from the RCA and supply the anterior right ventricular wall.
  • Posterior descending artery (PDA): Also known as the posterior interventricular artery. Arises from the RCA in the majority of cases. Runs in the inferior interventricular groove and supplies the diaphragmatic surface of the ventricles and part of the interventricular septum.
  • Posterior left ventricular artery (PLV): Also known as the posterolateral branch. Arises from the RCA in the majority of cases. Supplies the inferior left ventricular wall.
  • Septal perforators: Arise from the left anterior descending (LAD) artery and supply the anterior ventricular septum.
  • Diagnonal branches: Arise from the LAD artery and supply the anterior wall of the left ventricle.
  • Ramus intermedius: The most common variation in left coronary anatomy. A third branch that arises between the LAD and LCx at the distal left main coronary artery. The ramus intermedius artery may supply the anterior or the lateral wall of the left ventricle depending on its course.
  • Obtuse marginal branches: Arise from the LCx and supply the lateral wall of the left ventricle.
The origin of the PDA determines dominance. In a right-dominant heart, the PDA is supplied by the RCA. In a left dominant heart the PDA is supplied by the LCx. In a co-dominant heart, the PDA is supplied by the RCA and the PLV is supplies by the LCx.

References

  • Kini S, Bis KG, Weaver L. Normal and variant coronary arterial and venous anatomy on high-resolution CT angiography. AJR Am J Roentgenol. 2007 Jun;188(6):1665-74.
  • Abbara S and Achenbach S. Chapter 8: Coronary Computed Tomography Angiography. in Cardiac Imaging: The Requisites (third ed). Miller SW et al (eds).

Friday, February 5, 2010

Spring Ligament

The spring (plantar calcaneonavicular) ligament arises from the medial aspect of the calcaneus and attaches to the inferior and medial surfaces of the navicular bone. The spring ligament is composed of superomedial, inferior, and "third" ligaments:
  • Superomedial: Originates from the medial aspect of the sustentaculum tali and inserts in a fanlike manner to the superomedial aspect of the navicular bone close to the talonavicular joint.
  • Inferior: Also known as the inferoplantar calcaneonavicular ligament. Originates anterior to the middle articular facet of the calcaneus at the coronoid fossa anterior to the medioplantar oblique ligament (see below) and takes a slightly oblique course to attach in a fanlike manner at the inferior beak of the navicular bone. Located plantar and lateral to the superomedial ligament.
  • "Third": Also known as the medioplantar oblique calcaneonavicular ligament. Originates anterior to the middle articular facet of the calcaneus at the coronoid fossa and takes a medial oblique course to insert to the medioplantar portion of the navicular bone, just below its tuberosity. Located in the fatty tissue between the superomedial and inferior components
The spring ligament was initially thought to act as a spring for the longitudinal arch of the foot, but subsequent work has shown that it has no elastic properties. It does have two important functions, however. It supports the head of the talus and (together with the tibialis posterior tendon, the plantar fascia, and the plantar ligaments) stabilizes the longitudinal arch of the foot.

References

Thursday, February 4, 2010

Button Sequestrum

A round radiolucent skull defect with a central bony density is referred to as a button sequestrum. This finding can be seen in the following cases, but is an uncommon appearance in all (bold indicates classic cases)
  • Langerhans cell histiocytosis: Classic description. Most commonly affects the skull.
  • Osteomyelitis
  • Fibrosarcoma
  • Lymphoma
  • Partially calcified intraosseous lipoma
  • Tuberculous osteitis
  • Radiation necrosis
  • Metastatic carcinoma: Especially breast
  • Fibrous dysplasia
  • Epidermoid and dermoid cysts
  • Hemangioma: Mimics button sequestrum.
  • Meningioma
  • Paget disease
  • Multiple myeloma
  • Syphilis
  • Sarcoidosis

References

  • Gamuts in Radiology - Reeder and Felson - 4th ed (Springer, 2003).
  • Krasnokutsky MV. The button sequestrum sign. Radiology. 2005 Sep;236(3):1026-7.
  • Satin R, Usher MS, Goldenberg M. More causes of button sequestrum. J Can Assoc Radiol. 1976 Dec;27(4):288-9.

Wednesday, February 3, 2010

Well-Circumscribed Lesions on Mammography

Breast cancers that can appear as well-circumscribed masses on mammography include:
  • Medullary carcinoma:
  • Mucinous carcinoma:
  • Papillary carcinoma: Intraductal or intracystic
  • Invasive ductal carcinoma:
  • Ductal carcinoma in situ:
  • Primary lymphoma:
  • Metastasis:
  • Phyllodes tumor: Benign or malignant
  • Sarcoma of breast:
These usually turn out not to be completely well-circumscribed on magnification views.

References

Gamuts in Radiology - Reeder and Felson - 4th ed (Springer, 2003).

Tuesday, February 2, 2010

Gas in the Spinal Canal (Pneumorrhachis)

This was a puzzle on call a while back. An intoxicated man, found down, was brought in and sent to us for head and cervical spine CT. The head was negative, but the cervical spine CT showed two tiny pockets of gas in the anterior epidural space at the level of C4-C5 and C5-C6 on the right. What I finally settled on was that gas introduced into the venous system during IV access had made it to the epidural venous plexus just in time for the CT of the cervical spine. Another possibility was that gas from vacuum disc phenomenon had escaped into the epidural space with disc herniation. The patient was stable and clinical suspicion for a traumatic etiology (see below) was low, so he was monitored while he detoxified and released. If there had been clinical suspicion, a more thorough workup would have been indicated.

The differential diagnosis of gas in the spinal canal is wide:
  • Disc degeneration
  • Epidural abscess
  • Iatrogenic: e.g., thoracostomy tube placement, IV access
  • Blunt chest trauma: Gas from pneumothorax or pneumomediastinum (tracheal or esophageal rupture), when associated with a tear of the spinal meninges, can track into the spinal canal. A case of traumatic lung herniation into the epidural space has also been reported.
  • Blunt pelvic trauma: Gas from the gastrointestinal tract, when associated with a tear of the spinal meninges, can track into the spinal canal
  • Strenuous exercise
  • Skull fracture: Source may be gas the sinuses, mastoid air cells, or outside world.

References

  • Hwang WC, Kim HC. CT demonstration of spinal epidural air after chest trauma. Eur Radiol. 2000;10(2):396-7.
  • McIntosh SE, Salcedo-Dovi H, Cortes V. Air in the spinal canal associated with trauma. J Emerg Med. 2006 Jul;31(1):33-5.

Monday, February 1, 2010

Syntelencephaly

Syntelencephaly, also known as middle interhemispheric variant, is a mild subtype of holoprosencephaly that is characterized by an abnormal midline connection of the cerebral hemispheres between the posterior frontal and parietal regions. There is preserved interhemispheric separation of the basal forebrain, anterior frontal lobes, and occipital regions.

The images above show interhemispheric fusion of the gray matter and white matter across the midline and absence of the interhemispheric fissure in the posterior frontal and parietal lobes. The coronal image shows that the gyral pattern is abnormal with increased cortical thickness and irregularity of the cortical–white matter junction. On the sagittal view only the genu and splenium of the corpus callosum are present.

References

Simon EM, Hevner RF, Pinter JD, Clegg NJ, Delgado M, Kinsman SL, Hahn JS, Barkovich AJ. The middle interhemispheric variant of holoprosencephaly. AJNR Am J Neuroradiol. 2002 Jan;23(1):151-6.