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General Hospital Health Sciences Centre. Robert 0. Campbell, MD, FRCPC. Department of Medicine. St. Clare's Mercy Hospital. Robert L. Nolan, MD, FRCPC.
more common). Inflammatory lesions of the liver usually produce abnormal results of liver function tests, as described by Zipser and colleagues.' In their case the diagnosis of pseudotumour of the liver was established by laparotomy, and the morphologic appearance of the mass was similar to and confused with that of metastatic carcinoma. It is therefore likely that Forward and colleagues' patient had an extrahepatic, extraperitoneal tuberculous mass adjacent to the right lobe of the liver, similar to those described by Taylor and coworkers,2 which became evident clinically when the ascites disappeared. Laparoscopy would have been useful in the case described by Forward and colleagues to determine whether the mass was indeed in the liver. With the imaging modalities available today it should not be difficult to accurately describe unusual presentations of disease. Jacob Korula, MD, FRCPC

University of Southern California Liver Unit Rancho Los Amigos Hospital Downey, Calif.

References 1. Zipser RD, Rau JE, Ricketts RR et al: Tuberculous pseudotumor of the liver. Am J Med 1976; 61: 946-951 2. Taylor RH, McNicol MW: Ultrasound in the diagnosis of two unusual tuberculous abscesses. Br J Surg 1980; 67: 556-557

[Forward and colleagues reply.] Dr. Korula suggests that the hepatic pseudotumour that we described was an extrahepatic pseudotumour. We did, however, find liver tissue, albeit with somewhat distorted architecture, in the percutaneous biopsy specimen. We apologize for not making that clear in our case report. Korula was also surprised at the normal results of the liver function tegts; however, the results of these tests have been normal in several other confirmed cases of hepatic tuberculous pseudotumour or abscess.'-3 Even in the case cited by Korula the serum levels of glutamic oxaloacetic transaminase, glutamic pyruvic transaminase and bilirubin were within normal limits, and the serum alkaline phosphatase level was only twice the normal level.4 268

We examined many CT scans and ultrasonograms and are - confident that the mass was indeed in the liver parenchyma. Unfortunately, the puiblished reproductions of the ultrasonograms were less than optimal. Kevin R. Forward, MD, FRCPC Resident, medical microbiology Toronto General Hospital Toronto, Ont. Amy Y. Tong, MD, FRCPC Department of Medicine General Hospital Health Sciences Centre Robert 0. Campbell, MD, FRCPC Department of Medicine St. Clare's Mercy Hospital Robert L. Nolan, MD, FRCPC Department of Radiology General Hospital Health Sciences Centre St. John's, Nfld.

References 1. Pendse AK, Khamersa HL, Babel AL et al: Tuberculoma of the liver. J Indian Med Assoc 1981; 76: 175-176 2. Purohit VP, Verma R: Tuberculous liver abscess. J Postgrad Med 1982; 28: 221222 3. Rosin RD: Tuberculoma of the liver. Tubercle 1978; 59: 47-54 4. Zipser RD, Rau JE, Ricketts RR et al: Tuberculous pseudotumor of the liver. Am J Med 1976; 61: 946-951

How safe is diagnostic ultrasonography? I am pleased to see articles such as those by Drs. B. St. John Brown (1984; 131: 307-311) and Henry F. Muggah (ibid: 280, 282) in CMAJ. The authors' recommendations and conclusions should help doctors to fulfil their responsibility to use ultrasonography prudently. However, with this goal in mind, it is important that an oversight in St. John Brown's article be brought to attention: he does not identify the types of intensities mentioned in his discussion of adverse biologic effects. An understanding of these different types of intensities should be of use in promoting the prudent use of ultrasonography.' Furthermore, an apparent misinterpretation of the type of intensity led to an error in St. John Brown's discussion of transient cavitation. He says that transient cavitation occurs at intensities far above that

CAN MED ASSOC J, VOL. 133, AUGUST 15, 1985

regarded as the desired upper limit for pulsed ultrasound in diagnostic procedures. However, a significant number of pulsed ultr'asound devices yield intensities above those at which transient cavitation has been claimed to occur.2 Although the clinical implications of these claims are still highly speculative, the possibility of transient cavitation cannot be dismissed simply on the basis of St. John Brown's arguments. The topic is too complex to cover in a brief letter. However, for the interested reader the definitions of intensity and other aspects of the safety of diagnostic ultrasonography are thoroughly discussed in two recent and valuable publications.3'4 Stephen Bly, PhD Head Acoustics Unit Non-Ionizing Radiation Section Consumer and Clinical Radiation Hazards Division Health Protection Branch Department of National Health and Welfare Ottawa, Ont.

References I. Bioeffects Committee, American Institute of Ultrasound in Medicine: Safetli ConSiderations Jor Diagnostic Ultrasounid (pubi no 316), American Institute of Ultrasound in Medicine, Bethesda, Md, 1984 2. Stewart HF: Output levels from commercial diagnostic ultrasound equipment [abstrl. J Ultrasoiund Med 1983; (suppl): 39 3. Biological EJjfetts oJ Ultrasound: Mechanisins an1d Clinical Imiiplications (rep no 74), National Council on Radiation Protection and Measurements, Bethesda, Md, 1983 4. American Institute of Ultrasound in Medicine/National Electrical Manufacturers Association: Safety standard for diagnostic ultrasound equipment. J Ultrasound Med 1983; 2 (suppl): Si -S50

The Vancouver Lymphadenopathy AIDS Study: 3.

[correctioni In Table I of the article by Dr. William J. Boyko and his colleagues (133: 28-32) the absolute number of helper T cells per millilitre in the persistent generalized lymphadenopathy group should have been 649. We apologize for the error.-Ed.