Pericardial Effusions in HIV Infection

The above image is from a patient with a history of HIV and lymphoma. CECT demonstrates a thickened, enhancing pericardium with a complex pericardial effusion. Bilateral pleural effusions, right greater than left, are also noted. 

Pericardial effusions are the most common cardiovascular complication of HIV infection and usually carry a poor prognosis. The majority of cases are due to an idiopathic cause. Other causes that must be considered in this population are tuberculosis, bacterial infection (S. aureus is the most common), malignancy (lymphoma and Kaposi's sarcoma), viral, and fungal.


REFERENCES
Chen Y, Brennessel D, Walters J, et al. Human immunodeficiency virus-associated pericardial effusion: report of 40 cases and review of the literature. Am Heart J 1999;137(3):516-21.
Restrepo CD, Diethelm L, Lemos JA, et al. Cardiovascular complications of human immunodeficiency virus. Radiographics 2006;26:213-31.
Wang ZJ, Reddy GP, Gotway MB, et al. CT and MR imaging of pericardial disease. Radiographics 2003;23:S167-80.

Cystic Lesions of the Renal Sinus

Peripelvic Cysts

• multiple benign cysts arising in the renal sinus (extraparenchymal)
• likely originate from sinus lymphatics
• usually bilateral
• may mimic hydronephrosis on US and NCECT but cannot be traced to the ureter
• indistinguishable from renal sinus lipomatosis on excretory urography

Parapelvic Cysts

• simple cysts originating from the medial renal parenchyma
• same imaging features as simple renal cysts (Bosniak I)
• usually asymptomatic but a large parapelvic cyst that compresses the renal vasculature/collecting system may cause hypertension, hematuria, and hydronephrosis

REFERENCES

Rha SE, Byun JY, Jung SE, et al. The renal sinus: pathologic spectrum and multimodality imaging approach. Radiographics 2004;24:S117-31.

The Air Crescent Sign

The air crescent sign refers to a radiolucent rim around a soft tissue density and is characteristic of invasive pulmonary aspergillosis (or other angioinvasive fungal infections) in immunocompromised patients. It results when Aspergillus invades the pulmonary vasculature and causes hemorrhage with subsequent infarction of pulmonary tissue. Over time, the infarcted tissue retracts and is absorbed along its periphery by leukocytes which is what gives rise to the air crescent appearance. The visualization of the air crescent sign indicates a favorable outcome because patients without leukocyte function cannot form this consolidation.

The image above is from a patient with prior history of tuberculosis who presented with a cough. The air crescent sign is seen in the left upper lobe.


REFERENCES
Abramson S. The air crescent sign. Radiology 2001;18:230-2.

The Molar Tooth Sign - Joubert Syndrome

Joubert syndrome is an autosomal recessive disorder characterized by cerebellar vermian hypoplasia with a midline cleft and lack of decussation of the superior cerebellar peduncles, the latter causing an enlargement of the peduncles. Other decussation defects of the central pontine and corticospinal tracts as well as dysplasia of the olivary nuclei may also be present. Associated renal, retinal, and hepatic abnormalities are often seen. 

The molar tooth sign refers to the characteristic appearance of the midbrain seen on axial imaging (CT or MR) in patients with Joubert syndrome. Thickened superior cerebellar peduncles surrounding an elongated fourth ventricle give this appearance. A vermian cleft may also be recognized.


REFERENCES
McGraw P. The molar tooth sign. Radiology 2003;29:671-2.

Discitis/Vertebral Body Osteomyelitis

Vertebral body osteomyelitis (and associated discitis) is an infection involving the vertebral body endplates that extends to the intervening disc space. While vertebral body endplate destruction may be visible on plain films or bone CT studies, MR is the preferred imaging modality to assess for spread of infection to the disc space and paraspinal tissues, or for development of an epidural abscess. T1W images (A, D) will show endplate destruction and thickening of the paraspinal tissues with ill-defined fat places. T2W images (B) will demonstrate high signal in the intervertebral disc. Gadolinium enhanced images (C) will demonstrate enhancement of the infected vertebral bodies and paraspinal tissues. In the presence of an epidural abscess fluid sensitive sequences will show a collection in the epidural space that demonstrates peripheral enhancement upon gadolinium administration. 


REFERENCES
Dagirmanjian A, Schils J, McHenry M, et al. MR imaging of vertebral osteomyelitis revisited. Am J Roentgenol 1996;167(6):1539-43.
Kowalski TJ, Layton KF, Berbari EF, et al. Follow-up MR imaging in patients with pyogenic spine infections: lack of correlation with clinical features. Am J Roentgenol 2007;28:693-99.

Pulmonary Pseudotumors

Nodular Pulmonary Amyloid (Amyloidoma)

• one of the three presentations of amyloidosis in the chest (the other two are tracheobronchial and nodular septal)
• solitary or multiple nodules with smooth contours
• lower lobe, subpleural/peripheral location 
• may calcify or undergo osseous metaplasia
• larger nodules may cavitate or become hemorrhagic
• resection is diagnostic and curative
• differential - primary or metastatic neoplasms

Exogenous Lipoid Pneumonia

• caused by aspiration of mineral, vegetable, or animal oil present in food, radiologic contrast media, or oil based medications
• NECT will show low attenuation, mass-like consolidation, with regions of fat density
• crazy paving

REFERENCES

Gimenez A, Franquet T, Prats R, et al. Unusual primary lung tumors: a radiologic-pathologic overview. Radiographics 2002;22:601-19.

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