Round Atelectasis

Round atelectasis occurs adjacent to the pleural surface and is almost always asymptomatic. In about 70% of cases, there is a history of asbestos exposure, but any form of pleural thickening can be associated with round atelectasis.

Imaging Findings

The appearance is that of a rounded subpleural opacity that forms acute angles with the pleura. It is usually seen in the lower lobes posteriorly, and there is almost always adjacent pleural thickening. As in other forms of atelectasis, there is volume loss in the affected lobe. There may be air bronchograms within the mass, giving the appearance of cavitation (pseudocavitation).

The aunt Minnie is the comet tail sign, which is formed by vessels and bronchi of the affected collapsed lung that are pulled in as the lung collapses.

Theories

Two main theories attempt to explain how round atelectasis happens after a pleural effusion. One posits that round atelectasis is caused by infolding the visceral pleura into and surrounding an area of atelectasis. This somehow causes the lung to curl on itself. Then fibrous adhesions form that suspend the atelectatic segment and usually tilt the lung cranially. When the effusion resolves, aerated lung fills in the space between the area of round atelectasis.

Another theory proposes that local pleural irritation (e.g., by asbestos) cause contraction and thickening of the pleura in the setting of a pleural effusion. The underlying lung then shrinks, and a round area of atelectasis develops.

The main differential diagnosis is bronchogenic carcinoma.

Reference

Partap VA. The Comet Tail Sign. Radiology. 1999;213:553-554.

Embryology of Corpus Callosum

The corpus callosum forms between the 11th and 20th weeks. The anterior genu is the first part to form. Development then proceeds posteriorly: anterior body, followed by the posterior body and splenium. After all of this is done, development pays attention to the front again, forming the rostrum.

This is important in differentiating partial dysgenesis of the corpus callosum from a developmental injury when the splenium is not seen. Since the rostrum is the last to form, if you see a rostrum in the absence of a splenium, you know that the problem is injury to the splenium. If the rostrum is not seen, then the absent splenium is likely due to partial dysgenesis.

References

Loevner, LA. Case Review Series: Brain Imaging, 2nd edition.

Artery of Percheron

The artery of Percheron is a rare variant of the posterior aspect of thalamic blood supply. The thalami and the midbrain are supplied by both the anterior and posterior circulations.

Anterior Circulation

The anteroinferior aspects of the thalami and midbrain are supplied by the thalamoperforator arteries arising from the posterior communicating arteries.

Posterior circulation

The medial aspects of the thalami and midbrain are supplied via branches arising from P1 segments of the posterior cerebral arteries.

The lateral and superior aspects of the thalami are supplied by branches arising from the P2 segments of the posterior cerebral arteries.

The artery of Percheron refers to a single trunk that arises from one of the P1 segments and provides bilateral distribution.

Occlusion of the artery of Percheron causes bilateral infarctions in the medial aspects of thalami and brainstem.

References

Matheusa MG and Castilloa M. Imaging of Acute Bilateral Paramedian Thalamic and Mesencephalic Infarcts. AJNR Am J Neuroradiol. 2003 Nov-Dec;24(10):2005-8.

Recurrent Artery of Huebner

The recurrent artery of Huebner is the largest and longest of the penetrating branches of the anterior cerebral artery. It arises from either the proximal A2 segment, the A1 segment, or, less commonly, the anterior communicating artery. It terminates dorsal and slightly lateral to the carotid bifurcation.

The recurrent artery of Huebner and medial lenticulostriate arteries supply the caudate head, anterior limb of the internal capsule, and part of the basal ganglia.

Reference

Osborn AG, Chapters 5 and 6 in Diagnostic Cerebral Angiography (2nd ed). Lippincott, Williams, & Wilkins (1999).

Periapical Cyst

Periapical Cysts are the most common cyst of the jaw and are usually asymptomatic (as was this patient who presented for evaluation for trauma).

Periapical cysts are the result of periapical inflammation that occurs due to pulpal necrosis in a tooth (the pulp of a tooth is the central part of a tooth that contains odontoblasts).

Periapical cysts are usually less than 1 cm in diameter and are bordered by a thin rim of cortical bone. The radiographic appearance of periapical cysts and granulomas is similar. Periapical cysts are less common and often larger. Periapical cysts are treated by enucleation of the cyst lining and root canal.

In the case shown here, the periapical cyst has eroded into the maxillary sinus.

References

Scholl RJ, et al. Cysts and Cystic Lesions of the Mandible: Clinical and Radiologic-Histopathologic Review. Radiographics. 1999;19:1107-1124.

Differentiating Primary CNS Lymphoma from Toxoplasmosis

Cerebral toxoplasmosis and primary CNS lymphoma can present similarly both clinically and radiologically. PET and Thallium-201 brain SPECT can be used to help differentiate them.

Thallium-201 is sensitive for lesions larger than 2 cm. Initial and delayed (~4 hours) images are obtained. Lymphoma demonstrates increased activity on delayed images, while Toxoplasma demonstrates decreased activity over time.

With the advent of highly active antiretroviral therapy (HAART), however, new studies have found decreased specificity of Thallium-201 brain SPECT, presumably because of the improved immune response to Toxoplasmosis, resulting in increased uptake due to inflammatory cells. The increased numbers of patients with toxoplasmosis who demonstrate elevated uptake on Thallium-201 brain SPECT may make differentiation of toxoplasmosis and primary CNS lymphoma more difficult.

On PET, lymphoma shows high standardized uptake values (usually more than 3.5), while toxoplasmosis usually does not. PET has higher resolution than SPECT and can be used for smaller lesions. Of note: corticosteroid treatment may decrease F-18 FDG activity on PET.

References

• Giancola ML, Rizzi EB, Schiavo R, Lorenzini P, Schininà V, Alba L, Del Grosso B, Gigli B, Rosati S, Mango L, Bibbolino C, Antinori A. Reduced value of thallium-201 single-photon emission computed tomography in the management of HIV-related focal brain lesions in the era of highly active antiretroviral therapy. AIDS Res Hum Retroviruses. 2004 Jun;20(6):584-8.
• Lorberboym M, et al. Rapid Differential Diagnosis of Cerebral Toxoplasmosis and Primary Central Nervous System Lymphoma by Thallium-201 SPECT. The Journal of Nuclear Medicine. 1996 37 (7);1150-1154.

Tolosa-Hunt Syndrome and Idiopathic Orbital Inflammatory Pseudotumor

Tolosa-Hunt syndrome and idiopathic orbital inflammatory pseudotumor are both chronic granulomatous diseases with common clinical characteristics (painful ophthalmoplegia) and response to corticosteroid therapy. Tolosa-Hunt is characterized by inflammation of the cavernous sinus and/or superior orbital fissure, while idiopathic orbital inflammatory pseudotumor involves the orbit. There may be territorial overlap of the two entities.

Contrast-enhanced, thin-slice (axial and coronal) MRI of the cavernous sinus and fat-suppressed pre- and post-contrast images of the orbits are recommended for evaluation.

Tolosa-Hunt syndrome

Imaging may be normal or demonstrate inflammatory changes in the cavernous sinus, superior orbital fissure, and/or orbit. Suprasellar and parasellar tumor invasion of the cavernous sinus may have a similar appearance. Enlargement of the optic nerve or extraocular muscles may also bee seen. MRA may show narrowing of the cavernous portion of the internal carotid artery.

Inflammatory orbital pseudotumor

Inflammatory orbital pseudotumor most commonly involves the extraocular muscles and/or lacrimal gland. The margins are irregular and the lesion may look infiltrative, mimicking neoplasm or infection.

The most common pattern is termed myositic and involves the extraocular muscles (superior complex and medial rectus most common). The tendinous insertions are also involved, differentiating this entity from thyroid-associated orbitopathy (tendons are spared).

Isolated lacrimal gland involvement (case shown here) is the second most common pattern, with diffuse enlargement of gland in the anteroposterior dimension. Differential considerations include sarcoidosis and lymphoproliferative disorders.

Another pattern of involvement is isolated to the globe and retrobulbar orbit. There is thickened sclera with heterogeneous enhancement and variable involvement of the retrobulbar fat and optic nerve.

The least common pattern involves irregular thickening and enhancement of the optic nerve sheath. Differential considerations include optic neuritis.

A diffuse pattern may also be observed, involving several of the above patterns.

Reference

• Taylor DC. Tolosa-Hunt Syndrome. eMedicine, Mar 12, 2009.
• Wasmeier C, Pfadenhauer K, Rösler A. Idiopathic inflammatory pseudotumor of the orbit and Tolosa-Hunt syndrome--are they the same disease? J Neurol. 2002 Sep;249(9):1237-41.

Eye-of-the-Tiger Sign

Eye-of-the-tiger sign refers to a low intensity globus pallidus with a central region of high intensity in the anteromedial globus pallidus.

This is classically described in Hallervorden-Spatz syndrome. The complete differential diagnosis includes:

• CO poisoning
• Corticobasal ganglionic degeneration
• Hallervorden-Spatz syndrome: low T2 signal globus pallidus represents excess iron deposition. The central high signal is thought to involve gliosis and/or demyelination and axonal swelling.
• Leigh syndrome
• Neurofibromatosis
• Parkinson disease
• Progressive supranuclear palsy (Steele-Richardson-Olszewski syndrome)
• Shy-Drager syndrome
• Toxins

Reference

• Guillerman RP. The Eye-of-the-Tiger Sign. Radiology. 2000;217:895-896.
• Neuroradiology: The Requisites, 2nd edition. pp 391-932.

Dural Sinus Thrombosis: MRI

Sequence	Acute	Subacute
T1	iso	hyper
T2	hypo	hyper
FLAIR	hypo	hyper
GRE	blooms	blooms

Artery of Adamkiewicz

The artery of Adamkiewicz, also known as the great anterior radiculomedullary artery, connects to the anterior spinal artery and is the most important arterial supply of the thoracolumbar spinal cord.

The artery of Adamkiewicz is a third order branch of the left intercostal or lumbar arteries. These arteries divide into anterior and posterior branches. The anterior branch runs along the costal groove, while the posterior branch courses to the spine.

The posterior branch then trifurcates into the radiculomedullary artery, the muscular branch, and the dorsal somatic branch. The radiculomedullary artery in turn bifurcates into posterior and anterior radiculomedullary arteries. The artery of Adamkiewicz is the largest anterior radiculomedullary artery.

The artery of Adamkiewicz is important in surgical planning for patients with aortic aneurysms in order to prevent postoperative paraplegia or paraparesis.

References

Yoshioka K, et al. MR Angiography and CT Angiography of the Artery of Adamkiewicz: Noninvasive Preoperative Assessment of Thoracoabdominal Aortic Aneurysm. RadioGraphics 2003; 23: 1215-1225.

Segments of the Internal Carotid Artery

The internal carotid artery (ICA) can be divided into 7 segments:

• C1: Cervical segment - From the bifurcation to the carotid canal
  
  
• C2: Petrous segment - Enters the skull base at the carotid canal. Has vertical and horizontal subsegments, forming a genu.
  
  
• C3: Lacerum segment - Begins at the end of the petrous canal and ends at the petrolingual ligament. Travels above (not through) the foramen lacerum.
  
  
• C4: Cavernous segment - within the cavernous sinus. Has 3 subsegments: posterior vertical or ascending (longer), horizontal, and anterior vertical or ascending (shorter). The proximal dural ring forms the roof of the cavernous sinus and is continuous with the dura covering the inferolateral aspect of the anterior clinoid process.
  
  The meningohypophyseal trunk, also known as the posterior trunk, is usually seen on angiography arising posteriorly to supply the the pituitary gland (via the inferior hypophyseal artery) and the meninges overlying the tentorium (via the marginal tentorial artery, also known as the artery of Bernasconi-Cassinari) and the meninges overlying the clivus (via the clival branches).
  
  The persistent trigeminal artery (rare) typically arises from the distal posterior vertical segment.
  
  
• C5: Clinoid segment - The shortest segment. Bounded inferiorly by the proximal dural ring and distally by the distal dural ring, and located extradurally. Spans a wedge-shaped area along the superior aspect of the anterior genu.
  
  Internal carotid artery aneurysms arising from the clinoid segment have a lower risk of rupturing into the subarachnoid space than those arising from the supraclinoid segments.
  
  
• C6: Ophthalmic segment - Terminates just before the posterior communicating artery origin. It arches posteriorly and slightly superiorly and is located intradurally
  
  Internal carotid artery aneurysms arising from the supraclinoid segments have a higher risk of rupturing into the subarachnoid space than those arising from the clinoid segment.
  
  
• C7: Communicating (terminal) segment - Another small segment. Begins at the origin of the posterior communicating artery and ends at the bifurcation of the ICA into anterior and middle cerebral arteries.

Reference

• Alleyne CH, Coscarella E, Spetzler RF, Walker MT, Patel AC, Wallace RC. Microsurgical Anatomy of the Clinoidal Segment of the Internal Carotid Artery, Carotid Cave, and Paraclinoid Space. Barrow Quarterly - Volume 18, No. 1, 2002.
• Osborn AG, Chapters 3 and 4 in Diagnostic Cerebral Angiography (2nd ed). Lippincott, Williams, & Wilkins (1999).
• Thines L, Delmaire C, Le Gars D, Pruvo JP, Lejeune JP, Lehmann P, Francke JP. MRI location of the distal dural ring plane: anatomoradiological study and application to paraclinoid carotid artery aneurysms. Eur Radiol. 2006 Feb;16(2):479-88.

Cavernous Angioma

Cavernous angiomas are congential vascular hamartomas that are made up of sinusoidal collection of vessels without interspersed normal brain. Blood products of various ages, calcification, and gliosis are also present.

They are occult on angiography and demonstrate increased attenuation on CT. On MR, there is a hemosiderin rim (low signal on all sequences) surrounding areas of methemoglobin. GRE is the most sensitive sequence for the detection of cavernous angiomas.

The patient whose MRI is shown here presented with seizures. CT (not shown) was negative (even in retrospect). MRI showed a right cerebellar hemisphere lesion with a rim that was low on all sequences and had a nidus of increased signal. Post-contrast images (panel D) showed no enhancement. A: T1, B: T2, C: FLAIR, D: Post-contrast, E: GRE, F: DWI.

Simple parenchymal hemorrhages and hemorrhagic tumors may demonstrate similar signal intensity, but parenchymal hemorrhages will appear as slit-like cavities (cavernous angiomas are round) and tumors will not have a complete rim of hemosiderin.

Reference

Neuroradiology: The Requisites, 2nd edition. pp 231-234.

Insertable Cardiac Monitors

These devices were a mystery to me for a while. Thanks to a helpful clinic note, it turns out that they're called implantable loop recorders or insertable cardiac monitors (Medtronic Reveal, in this case). The top one had a dead battery and was switched for a newer version (below).

MRI may move the device, but according to Medtronic "the device does not represent a safety hazard." The magnetic field may interfere with the data being stored by the device. Also, "MRI scans should be performed only in a specified MR environment under specified conditions as described in the device manual."

References

Reveal Web Page

Ivor Lewis Esophagectomy

The Ivor Lewis esophagectomy is a two-stage procedure for resection of masses in the middle or distal third of the esophagus. The first stage involves an abdominal incision to mobilize and resect part of the stomach. The second stage involves a right chest wall entry to perform the esophagogastrostomy.

First described in 1946 by Ivor Lewis, the procedure has been modified for laparoscopy.

References

Lewis I. The surgical treatment of carcinoma of the esophagus, with special reference to a new operation for growths of the middle third. Br J Surg 1946; 34:18–31.

Intra-arterial FLAIR Hyperintensity

Arterial segments proximal and distal to areas of stenosis or occlusion have been shown to demonstrate high signal on FLAIR images. This finding is seen in acute stroke and may be transient.

Increased FLAIR signal is thought to reflect altered hemodynamic and is seen with high grade of collateral circulation. Here we see intra-arterial FLAIR hyperintensity in the basilar artery.

Reference

Sanossian N, et al. Angiography Reveals That Fluid-Attenuated Inversion Recovery Vascular Hyperintensities Are Due to Slow Flow, Not Thrombus. Am J Neuroradiol, 2009; 30(3): 564-568.

Hyperechoic Renal Medulla

Hyperechoic renal medulla may be seen with the following conditions:

• Dehydration/Sepsis
• Medullary nephrocalcinosis:
  • Hypercalcemia:
    • Hyperparathyroidism: Primary or secondary
    • Bone destruction/turnover: Metastatic disease, Paget, osteoporosis, immobilization (especially, especially in infants)
    • Medications: Milk-alkali syndrome (ingestion of lots of calcium), hypervitaminosis D, furosemide (especially in children).
  • Renal tubular acidosis: Type 1 (distal).
  • Medullary sponge kidney (image shown above): Tiny calculi in dilated tubules. Usually asymptomatic, but may be complicated by nephrolithiasis, denal calculi, and urinary tract infection.
    
    
  • Sarcoidosis:
  • Syndromes: Williams, Hurler, Bartter, Achondroplasia.
• Renal papillary necrosis: Multifactorial process. Most common causes are pyelonephritis, analgesic nephropathy, and diabetes. Trivia: Beethoven's autopsy revealed renal papillary necrosis, possibly due to his alcohol and analgesic abuse, cirrhosis, and diabetes.

There's a stupid mnemonic for medullary nephrocalinosis that, like all such mnemonics, is 1) too long to be of any use, and 2) sacrifices relevance for the sake of the acronym. It is repeated here for the sake of completeness: Stadiumm Ditch (Sarcoidosis, Tuberculosis, A (vitamin), D (vitamin), Immobilization, Milk-alkali syndrome, Medullary sponge kidney, diuretics (furosemide in children), Idiopathic (especially in neonates/infants with Williams syndrome), Thyrotoxicosis, Carcinoma, Hyperparathyroidism).

Papillary necrosis also has a mnemonic, Postcards: Pyelonephritis, Obstruction of the urinary tract, Sickle cell, Tuberculosis, Cirrhosis of the liver, Alcoholism, Analgesic abuse, Renal transplant rejection, Diabetes mellitus, Systemic vasculitis.

References

• Gamuts in Radiology - Reeder and Felson - 4th ed (Springer, 2003).
• Khan AN, MacDonald S, Chandramohan M, Chandramohan H. Nephrocalcinosis. eMedicine. Updated: Jul 10, 2008.
• Shultz PK, Strife JL, Strife CF, McDaniel JD. Hyperechoic renal medullary pyramids in infants and children. Radiology. 1991 Oct;181(1):163-7.

Resistive Index: Role in Renal Colic

There appears to be some controversy about this issue. One camp maintains that the resistive index (RI) is an insensitive tool for differentiating obstructive and nonobstructive calculi in patients with acute renal colic. The opposing view is that RI can distinguish obstructed and unobstructed kidneys (with an RI> 0.7 seen in the symptomatic kidney).

References

• Gurel S, et al. Correlation Between the Renal Resistive Index (RI) and Nonenhanced Computed Tomography in Acute Renal Colic. J Ultrasound Med. 2006; 25:1113-1120.
• Onur MR, et al. Role of resistive index in renal colic. Urol Res. 2007;35(6):307-12.

Limbus Vertebrae

Limbus vertebra refers to the herniation of the disc under the ring apophysis before it fuses with the vertebral body. It presents as an oblique defect toward the outer surface of the vertebral body, most commonly at its anterior and superior border.

It can simulate fracture. The patient shown in this case had a CT of the abdomen at an outside institution that was interpreted as an L4 fracture. He had a CT and MR of the lumbar spine that were characteristic for a limbus vertebra.

Reference

R Kumar et al. The vertebral body: radiographic configurations in various congenital and acquired disorders. RadioGraphics 1988; 8: 455-485.

Normal Hepatic Artery Velocity in Portal Vein Thrombosis

Hepatic artery (HA) velocity is increased with portal vein thrombosis (PVT). This is responsible for the increased arterial-phase enhancement of the liver parenchyma supplied by the thrombosed veins.

In this image we see an enlarged hepatic artery (red) anterior to a thrombosed portal vein.

Normal values for HA peak velocities are hard to come by. Normal subjects in one study had mean HA velocities of less than 0.7 m/s. In this image (same patient as the first image) we see that the hepatic artery peak systolic velocity is greater than 2.5 m/s.

It has also been shown that HA resistance decreases with acute portal vein thrombosis. Control subjects in one study had mean HA resistive indices (HARI) of 0.75 +/- 0.08, while those with PVT had HARIs of 0.57 +/- 0.11. The reduction in HARI may not be as apparent with more chronic PVT.

References

• Platt et al. Hepatic artery resistance changes in portal vein thrombosis. Radiology 1995; 196 (1): 95-98.
• Rokni-Yazdi H and Sotoudeh H. Assessment of Normal Doppler Parameters of Portal Vein and Hepatic Artery in 37 Healthy Iranian Volunteers. Iran J Radiol, 2006; 3(4): 213-216

Persistent Hyperplastic Primary Vitreous

Persistent hyperplastic primary vitreous (PHPV) is a congenital condition caused by incomplete regression of the embryonic ocular blood supply. On physical examination, there is Leukocoria (white retinal light reflex)

Anteriorly, we see soft tissue behind the lens that corresponds to the persistent hyperplastic primary vitreous. Posteriorly, there is a stalk of hyaloid remnant that extends from this structure to the retina.

PHPV may present as an isolated anterior form (best prognosis for preserved vision), isolated posterior form, or combined form (most common). Unilateral involvement is three times more common than bilateral involvement.

On cross-sectional imaging, there is a hyperattenuating/hyperintense small globe with soft tissue behind the lens. No calcification is seen.

Differential considerations for leukocoria with microphthalmia include PHPV (if unilateral) and retinopathy of prematurity and PHPV (if bilateral). For completeness, leukocoria in a normal-sized eye can be seen with calcifications in retinoblastoma and retinal astrocytoma and without calcifications in toxocaral endophthalmitis, and Coats disease.

Carotid Artery Pseudo-Occlusion

Carotid artery pseudo-occlusion (CAPO), also known as preocclusive stenosis, the carotid slim sign, and the carotid string sign, refers to incomplete ICA occlusion and may be misdiagnosed at angiography as complete occlusion. The distinction is important because while CAPO carries a pretty high stroke risk (~25% within three years), complete internal carotid artery occlusion has a relatively benign prognosis.

The string sign is a thin, antegrade trickle of contrast material in the internal carotid artery distal to an occlusion. The lumen distal to the occlusion is collapsed, leading to diminished flow.

References

• Berman SS, et al. Distinguishing Carotid Artery Pseudo-Occlusion With Color-Flow Doppler. Stroke. 1995;26:434-438
• Greiner C, et al. Revascularization procedures in internal carotid artery pseudo-occlusion. Acta Neurochir (Wien). 2004 Mar;146(3):237-43;
• Pappas JN. The Angiographic String Sign. Radiology 2002;222:237-238.
• Verlato F, et al. Clinical outcome of patients with internal carotid artery occlusion: a prospective follow-up study. J Vasc Surg. 1995; 32:293–298.

Hydranencephaly, Alobar Holoprosencephaly, and Massive Hydrocephalus

The main differential considerations for very large ventricles (> 20 mm) on prenatal ultrasound are hydranencephaly, alobar holoprosencephaly, and massive (maximal) hydrocephalus.

Hydranencephaly is thought to arise from bilateral internal carotid artery occlusions with intact posterior circulation. This results in a large cerebrospinal fluid space anteriorly where the frontal and temporal lobes would have formed and intact areas in the posterior circulation, namely preserved thalami. The third ventricle will be normal. You will also see a falx.

Holoprosencephaly is caused by the failure of division of the forebrain (specifically the prosencephalon). There are varying degrees of frontal lobe fusion. There may or may not be associated facial anomalies. Alobar holoprosencephaly is the most severe form and is characterized by a monoventricle communicating with a dorsal cyst; fused thalami, basal ganglia, and choroid plexus; and absent third ventricle, interhemispheric fissure, and corpus callosum. A ridge of tissue arising from the posterior aspect of the boomerang-shaped frontal lobes separates the monoventricle from the dorsal cyst. This ridge corresponds to the hippocampal fornix and is sometimes referred to as the hippocampal ridge.

Finally, in massive (maximal) hydrocephalus, there is a falx and separate ventricles with a septum pellucidum. The cortex, although squeezed extremely thin due to the large ventricles (circumferential mantle), can be seen (best with MRI). The third ventricle is dilated. Look for aqueductal stenosis.

References

• Filly RA, Chinn DH, Callen PW.. Alobar holoprosencephaly: ultrasonographic prenatal diagnosis. Radiology. 1984 May;151(2):455-9.
• Neuroradiology: The Requisites
• Yassin OM, El-Tal YM. Solitary maxillary central incisor in the midline associated with systemic disorders. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 1998 May;85(5):548-51.

Ductal Plate

The ductal plate is a sleeve of liver progenitor cells that forms around the portal vein and is the embryological precursor of the biliary system. Malformations of the ductal plate result in segmental dilatation of the intrahepatic bile ducts and variable degrees of fibrosis.

Ductal plate malformations include:

• biliary hamartoma: Also known as a von Meyenberg complex. Usually multiple lesions that follow water attenuation or intensity on CT and MR, respectively and measure less than 1.5 cm diameter. Enhancement depends on degree of fibrous or cystic makeup. Predominantly fibrous lesions become isoattenuating to liver on enhanced images, while predominantly cystic lesions become hypoattenuating to liver on enhanced images. They may be confused with hepatic metastases on imaging, and biopsy is needed for diagnosis.
• mesenchymal hamartoma:
• autosomal dominant polycystic kidney disease:
• autosomal recessive polycystic kidney disease:
• hepatic cyst:
• Caroli disease:

Intrahepatic Peripheral Cholangiocarcinoma: Path Issue

Cholangiocarcinoma is an adenocarcinoma that affects the bile ducts from the terminal ductules to the ampula. Intrahepatic peripheral cholangiocarcinoma (IPC) may be mistaken for colon cancer metastases on pathology. A primary colon cancer, therefore, should be excluded when cholangiocarcinoma is suspected. This is especially important in patients with ulcerative colitis, who are at risk for both colon cancer and cholangiocarcinoma.

Radiographic, Sonographic, and MRI Appearance of the Essure Device

The Essure microinsert is a hysteroscopically placed permanent contraceptive device made of an inner flexible metallic coil surrounded by an outer metallic coil. The ends of each coil have radiopaque markers.

The device measures 4 cm in length. The inner coil sticks out at one end, and the outer coil sticks out at the other. The inner coil end is inserted into the fallopian tube. The device is considered optimally placed when 5-10 mm of the outer coil stick out into the endometrial cavity.

Hysterosalpingography can be used to document the position of the device and patency of the tubes after device placement. Here we see a scout view of a hysterosalpingogram showing two micro-inserts on the right and one on the left.

On ultrasound, the outer coil shows up as two parallel interrupted echogenic lines that protrude into the endometrial cavity. The central coil may or may not be seen.

On MRI, there is linear loss of signal in the region of the fallopian tubes.

Complications include device expulsion, tubal perforation, and pregnancy.

References

Wittmer MH, et al. Sonography, CT, and MRI appearance of the Essure microinsert permanent birth control device. AJR Am J Roentgenol. 2006 Oct;187(4):959-64.

Misty Mesentery

The term misty mesentery was coined by Mindelzun et al to "describe the CT appearance of mesenteric fat infiltrated by inflammatory cells, fluid (edema, lymph, and blood), tumor, and fibrosis."

Misty mesentery is seen when the mean density of mesenteric fat increases from <-100 to -40 to -60 HU. The mesenteric vessels may also lose their sharp borders with the surrounding fat. The patient shown here was treated for non-Hodgkin lymphoma. There is a group of mesenteric lymph nodes with increased attenuation in the surrounding fat.

Misty mesentery can be idiopathic or be seen with

• Mesenteric panniculitis
• Edema/lymphedema
• Hemorrhage
• Tumor

At least one group has subdivided misty mesentery into segmental or nonsegmental types. They don't give a definition of nonsegmental misty mesentery, but state that it occurs most commonly in the setting of inflammatory bowel disease or trauma adjacent to the involved bowel.

They define segmental misty mesentery as increased attenuation of the fat around mesenteric vessels with a segmental distribution along the branches of the mesenteric vessels (jejunal, ileal, and ileocolic vessels). Segmental misty mesentery may be seen with mesenteric panniculitis, but not all cases of segmental misty mesentery are necessarily due to mesenteric panniculitis.

References

• Mindelzun et al. The Misty Mesentery on CT: Differential Diagnosis. AJR. 1996;167 (1): 61.
• Seo BK, Ha HK, Kim AY, Kim TK, Kim MJ, Byun JH, Kim PN, Lee MG, Yang SK, Yu ES, Kim JH. Segmental misty mesentery: analysis of CT features and primary causes. Radiology. 2003 Jan;226(1):86-94.

Swyer-James Syndrome

Swyer-James syndrome (SJS), also known as Macleod syndrome, refers to hypoplasia of a portion of or the whole lung caused by postinfectious obliterative bronchiolitis. It is thought to occur following acute bronchiolitis in infancy or early childhood. This early insult results in damage to the terminal and respiratory bronchioles, preventing normal development of alveolar buds.

Radiographic manifestations of SJS include pulmonary hyperlucency and pruning of vessels. On this radiograph, we can see that the left lung is smaller and more lucent compared to the right. In addition, the pulmonary vessels on the left are smaller and don't extend as far peripherally as those on the right.

CT demonstrates pruning of vessels and a mosaic attenuation pattern. Expiratory images show air trapping. On this coronal reformation, we can see decreased caliber of vessels on the left, with a relative hyperlucency.

References

• Ghossain MA, et al. Swyer-James syndrome documented by spiral CT angiography and high resolution inspiratory and expiratory CT: an accurate single modality exploration. J Comput Assist Tomogr. Jul-Aug 1997;21(4):616-8.
• Marti-Bonmati L, et al. CT findings in Swyer-James syndrome. Radiology. 1989 Aug;172(2):477-80.

Axillary Subsegment of the Right Upper Lobe

In about 15% percent of people, an independent limb of the posterior right upper lobe bronchus supplies an axillary subsegment. Disease localized to the axillary subsegment has a characteristic appearance on chest radiographs and CTs.

On PA images of the chest, disease of the axillary subsegment can resemble that of the anterior segment: a triangular opacity with its base abutting the right lateral chest wall, and the apex pointing toward the right hilum.

Differentiation can be made on the lateral view: the opacity is 4-sided and has sharp inferior (minor fissure) and posterior (major fissure) borders whose junction forms a wing-shaped lower border.

Reference

MacGregor JH, et al. Imaging of the axillary subsegment of the right upper lobe. Chest 1986;90;763-765

Inferior Vena Cava Filter Penetration

This can look scary the first time you see it. The limbs of the inferior vena cava filter were outside the lumen of the inferior vena cava. After discounting motion artifact, the only possibility left was that the limbs had actually dug their way out of the inferior vena cava. It's a not uncommon occurrence with inferior vena cava filters, and as long as the filters don't penetrate adjacent structures (bowel, aorta, pancreas, vertebral bodies), it's usually not of concern.

References

• Al-Basheer MA, et al. Chronic pain syndrome caused by a Bird's Nest filter: first case report. Cardiovasc Intervent Radiol. 2008 Jul;31 Suppl 2:S182-4.
• DuraiRaj R, Fogarty S. A penetrating inferior vena caval filter. Eur J Vasc Endovasc Surg. 2006 Dec;32(6):737-9.
• Putterman D, Niman D, Cohen G. Aortic pseudoaneurysm after penetration by a Simon nitinol inferior vena cava filter. J Vasc Interv Radiol. 2005 Apr;16(4):535-8.
• Sadaf A, et al. Significant caval penetration by the celect inferior vena cava filter: attributable to filter design? J Vasc Interv Radiol. 2007 Nov;18(11):1447-50.

Retroperitoneal Sarcomas

Retroperitoneal sarcomas (excluding Kaposi) make up about 10% of all sarcomas. The most common retroperitoneal sarcomas are liposarcoma and leiomyosarcoma, which each make up about 30% of cases, followed by malignant fibrous histiocytoma (15%).

Reference

Mack TM. Sarcomas and other malignancies of soft tissue, retroperitoneum, peritoneum, pleura, heart, mediastinum, and spleen. Cancer 1995; 75(suppl 1):211-44.