Acute Tubular Necrosis

Tc-99m MAG3 renal scan of a renal transplant recipient, day 1 after transplant with oliguria, shows delayed excretion of tracer from the transplant kidney. Images in vascular phase (not shown) are normal (normal perfusion and uptake).

Facts

• May occur immediately or after an initial short period of allograft function
• Related to both donor and recipient factors
• More common in cadaveric kidneys of older donors who sustained warm ischemia time or prolonged hypotensive periods
• Presented with oliguria or anuria early after transplant
• Diagnosis made by exclusion of other factors. Traditional signs (tubular casts, low urine osmolality) not reliable if patients with native partially functioning kidneys
• Treatment: supportive, return to dialysis if anuric (expected recovery of renal function usually within 3 weeks)

Renal Scan

• Normal perfusion, variable uptake but no (or delayed) excretion
• Serial scans helpful in determining viability of oliguric kidneys, predicting recovery or deterioration

Reference:

Resnick MI, Older RA. Diagnosis of Genitourinary Disease, 2nd edition, 1997

Renal Artery Aneurysm

Axial CT image shows a large partially thrombosed aneurysm of the right renal artery, which is extraparenchymal. On other images, the aneurysm is saccular, and appears to arise from the segmental artery.

Facts:

• True aneurysms involve all layers of the artery and usually inherited. They can be fusiform or saccular, and are more commonly extraparenchymal in location. Example: fibromuscular dysplasia, Ehlers-Danlos
• False aneurysms involve only some layers of the artery, usually are acquired and saccular. Examples: trauma, iatrogenic, dissection, mycotic
• Intrarenal aneurysms are intraparenchymal, can be either true or false aneurysm. Examples: polyarteritis nodosa, tuberculosis, neurofibromatosis

Indications for Intervention

• Symptomatic: rupture, pain, ischemia, infarction, hypertension
• Diameter more than 2 cm, enlarging or dissection
• Female patient who is pregnant, or contemplating pregnancy

Our case: False aneurysm probably due to dissection, surgical removal was performed in this symptomatic patient

Reference:

Lew WK, Weaver FA, Otero CA, et al. Renal artery aneurysm. E-medicine, updated September 17, 2008

Primary Brachial Plexus Tumor

Case Contributor: Gopalaratnam Balachandra, M.D.

Editor: Rathachai Kaewlai, M.D.

Coronal T1W and T2W MR images of the brachial plexus show a fusiform-shaped mass (large arrows) along the course of the right cervical nerve root (small arrow). The mass demonstrates heterogeneous low T1 and high T2 signal intensity. It has smooth, well circumscribed borders.

Axial T1W post contrast MR image shows heterogeneous enhancement of the mass (arrows) with a central area of non-enhancement.

Facts: Primary Brachial Plexus Tumor

• Rare tumor, most commonly benign with good prognosis after surgical resection
• Clinical presentations: pain, paresthesia, palpable mass
• Common pathology: schwannoma, neurofibroma. Other possibilities: malignant peripheral nerve sheath tumor (MPNST), desmoid, ganglion, epidermoid

Imaging

• MRI is the study of choice to delineate the margins of tumor from surrounding tissues
• Characteristic feature on any imaging techniques is close relationship with the parent nerve, which helps to exclude other possibilities such as lymphadenopathy, vascular anomalies, etc.
• Low signal on T1, high signal on T2 and heterogeneous enhancement
• MRI cannot differentiate schwannoma from neurofibroma

This case - Schwannoma of the brachial plexus in a 32-year-old woman who presented with pain in the right arm and right neck mass.

References:

1. Binder DK, Smith JS, Barbaro NM. Primary brachial plexus tumors: imaging, surgical, and pathological findings in 25 patients. Neurosurg Focus 2004;16.

2. Rettenbacher T, Sogner P, Springer P, et al. Schwannoma of the brachial plexus: cross-sectional imaging diagnosis using CT, sonography, and MR imaging. Eur Radiol 2003;13:1872-1875.

About Case Contributor: Dr. Balachandra is the head of the Department of Radiology at Government General Hospital in Pondicherry, S. India.

Colonic Closed Loop Obstruction

Supine radiographic study of a 41-year-old woman shows a focally dilated loop of large bowel (star) in the right side of the abdomen. There is little gas in the more distal colon.

Axial CT image shows a dilated right colon (star) with a transition point with a 'whirl-like' appearance (shown on contiguous images) in the mid abdomen (arrow). The rest of the colon is not dilated. Findings are most concerning for closed loop obstruction.

Facts: Closed Loop Obstruction of the Colon

• Colonic obstruction is rarely caused by postoperative adhesion (less than 1%). It is most commonly due to tumor
• CT should be the next imaging work-up to look for a mass. Contrast enema should be omitted due to the risk of perforation
• Closed loop obstruction of the colon usually is due to volvulus, which can be sigmoid (80%), cecal (15%) or involving the transverse colon (5%). Long mesocolon can predispose to malrotated cecum and result in a bascule or volvulus
• Signs of closed loop obstruction on imaging include focally dilated bowel loop with little gas distally and proximally, transition point with a whirl-like appearance at the mesenteric root, mesenteric haziness and free fluid

Our case: transverse colonic closed loop obstruction due to extralong colonic mesentery

Reference:

Halpert RD. Gastrointestinal imaging case review series, 2nd ed, 2008.

Brenner Tumor of the Ovary

Ultrasound image of the right ovary shows a well-circumscribed complex mass (arrows) with cystic and solid components (arrowheads) in a 66-year-old woman with abnormality seen on CT scan.

Facts: Complex Ovarian Mass

• Long list of potential causes, encompassing tumor (primary and neoplastic), inflammation and infection in a postmenopausal woman
• Potential tumors: serous and mucinous cystadenoma/cystadenocarcinoma, teratoma, clear cell carcinoma, endometrioid carcinoma, necrotic primary or metastatic tumors
• Most of these (if we think it is neoplasm) would need to be diagnosed histologically because imaging findings are nonspecific and malignancy cannot be excluded

Facts: Brenner Tumor

• Uncommon ovarian neoplasm, usually incidentally found
• Women in 5th to 7th decade of life
• Predominantly solid, but can be complex with cystic components when associated with serous and mucinous cystadenomas (seen in up to 30% of cases)
• Can be benign, borderline or malignant

Our case: Brenner tumor with struma ovarii on histology.

Reference:

Green GE, Mortele KJ, Glickman JN, Benson CB. Brenner tumors of the ovary sonographic and computed tomographic imaging features. J Ultrasound Med 2006;25:1245-1251.

Anatomic Position of Heart Valves

PA and lateral chest radiographs demonstrate anatomic position of three heart valves, A = aortic, M = mitral and T = tricuspid, in a patient with rheumatic valve disease. Note that the tricuspid prosthesis is an annuloplasty.

Facts

• The three heart valves (aortic, mitral and tricuspid) commonly overlap each other on frontal radiograph. Correct radiographic identification can be difficult.
• To differentiate the mitral from aortic valve on lateral view, one draws a line from the junction of the sternum and diaphragm to the carina. This line normally intersects aortic valve*. The valve below the line is mitral valve. The tricuspid valve is the one to the mitral valve.
• Without a lateral view, the best criterion for use in differentiating between aortic and mitral prostheses is the direction of flow (discernable in Starr-Edwards and most Bjork-Shiley prostheses). Orifice (en face or in profile) and orientation (vertical or horizontal) of prosthesis are less reliable.

* This may not always be true in patients who have deformed anterior chest wall or markedly enlarged right ventricle.

Our patient's mitral and aortic prostheses are disc type, so their direction of flow was not discernable.

Reference:

1. Gross BH, Shirazi KK, Slater AD. Differentiation of aortic and mitral valve prostheses based on postoperative frontal chest radiographs. Radiology 1983;149:389-391.

2. Miller SW, Boxt LM, Abbara S. Cardiac Imaging the Requisites, 3rd edition, 2009.

Scimitar Syndrome

Author: Santip Srisuwan, M.D.

Fig. 1: Chest radiograph of an asymptomatic young woman shows small right lung volume with cardiomediastinal shift toward the right side, small right hilum and a characteristic scimitar-shaped structure in the right lower lobe (arrow).

Figs 2&3: Contrast-enhanced CT images (maximal intensity projection, and 3D volumetric images) show an anomalous right lower lobe pulmonary vein (arrows) descending vertically, draining the right lower lobe and entering the IVC.

Facts: Scimitar Syndrome

• Also known as venolobar syndrome, hypogenetic lung syndrome
• Associations: congenital heart disease 25% (usually atrial septal defect)
• Symptoms: usually asymptomatic. Patients may have dyspnea if there is a large left to right shunt

Imaging Findings

• Small right lung
• Diminutive right hilum
• Dextroposition of the heart
• Characteristic scimitar vein draining below the diaphragm

Reference:

Hansell DM, et al. Imaging of diseases of the chest. Elsevier Mosby, 4th edition, 2005.

About Guest Author: Dr. Santip Srisuwan is a radiologist at Samitivej Hospital, Bangkok, Thailand.

Ankylosing Spondylitis (AS)

Frontal radiograph of the lumbar spine shows fusion of the sacroiliac joints (arrowheads) and thin syndesmophytes along the lateral borders of the lumbar spine.

Facts: AS

• Prototype of seronegative spondyloarthropathies (SNSA), which is a group of disorders of chronic inflammation of sacroiliac joints and spine
• Frequency: about 0.1% - 6% across different population (most likely toward the lower end)
• Genetic risk factor = human leukocyte antigen (HLA)-B27
• Principal bone/joint abnormalities = sacroilitis, synovitis and enthesitis

Imaging Findings

• Imaging findings are incorporated into the modified New York criteria for ankylosing spondylitis, as one of the four criteria.
• Sacroilitis: pseudowidening, sclerosis, erosions and later ankylosis
• Grading of sacroilitis on radiographs can be viewed here (link to Google Document provided by Schering-Plough Ply)

Modified New York Criteria for AS

Definite AS if 4a or 4b AND any clinical criteria (1-3)

1. Low back pain for at least 3 months' duration improved by exercise and not relieved by rest

2. Limitation of lumbar spine motion in sagittal and frontal planes

3. Chest expansion decreased relative to normal values for age and sex

4a. Unilateral sacroilitis grade 3-4

4b. Bilateral sacroilitis grade 2-4

Reference

Kippel JH. Primer on the rheumatic diseases, 13rd ed, 2008.

Peritonsillar Abscess

Axial CT image shows a multilocular low density collection (arrow) beneath the enlarged right tonsil (arrowhead), which is displaced medially.

Facts: Peritonsillar Infection

• Peritonsillar space is a space between anterior and posterior tonsillar pillar, deep to the tonsillar capsule and below the superior pharyngeal constrictor muscle
• Infection of this space usually arises from tonsillitis or pharyngitis, which can lead to peritonsillar cellulitis or abscess

Differentiation between Cellulitis and Abscess

• Differentiation of cellulitis from abscess has a clinical value, since cellulitis is treated medically but abscess usually requires surgical drainage
• Clinical distinction of the two can be difficult; imaging such as contrast-enhanced CT or ultrasound have been utilized for this purpose
• On CT, abscess appears as a cystic/multilocular low density collection with enhancing rim, with or without presence of gas at the center. Cellulitis appears as homogeneous soft tissue swelling with obliteration of fat planes.

References

1. Domino FJ. the 5-minute clinical consult 2007, 2007.

2. Sakaguchi M, Sato S, Asawa S, Taguchi K. Computed tomographic findings in peritonsillar abscess and cellulitis. J Laryngol Otol 1995;109:449-451.

Meningioma

Figure 1: Axial unenhanced CT image of the brain shows an isodense mass in the left posterior fossa with minimal, if any, mass effect.
Figure 2: Axial contrast-enhanced T1W MR image shows a large homogeneously enhancing extra-axial mass (star) near the left petrous bone overlying the sigmoid venous sinus (arrow).

Facts: Meningioma

• Tumors of meningeal cells (typically arising from meninges but can also be found in the choroid plexus, tela choroidea and arachnoid villi); therefore meningiomas can be seen in the meninges, spinal canal, intraventricular, and pineal regions
• Common, greater than 20% of all primary intracranial neoplasms
• Female:male = 3:2 to 2:1; mostly in late middle age
• Pathology: benign, atypical and malignant

Imaging Features

• Homogeneous, lobulated, well-circumscribed mass with uniform dense enhancement following contrast administration
• Common locations: parasagittal > convexity > sphenoid ridge
• High attenuation on unenhanced CT, iso- to mildly hypointense on T1W MR images
• May calcify in up to 1/4 of all cases, best seen on CT. Calcifications can be microscopic, punctate, large, peripheral or central. Malignant meningiomas rarely calcify.
• Hyperostosis can be seen in up to 1/2 of cases that meningiomas are immediately adjacent to the bone. Common in 'en plaque' meningioma
• Uncommon to have bone destruction (if pure destruction think of metastasis, sarcoma or myeloma)

Our case: benign meningioma overlying the sigmoid sinus without invasion. It is important to note if the meningioma is adjacent vascular structures for optimal surgical planning.

References:

1. Drevelegas A. Imaging of brain tumors with histological correlation, 2002.

2. DeAngelis LM, Gutin PH, Leibel SA. Intracranial tumors: diagnosis and treatment, 2002.