Central lucency of pelvic phleboliths:

Comparison of radiographs and noncontrast helical CT

Jong Chul Kim*

Department of Diagnostic Radiology, Chungnam National University Hospital, 640 Daesa-dong, Jung-gu, Taejon, 301-721, South Korea

Received 20 October 2000

Abstract

To compare how often the central lucency of pelvic phleboliths is seen on plain radiographs and noncontrast helical computed

tomography (CT), both images in 70 patients with renal colic were analyzed. Both images revealed the same number of phleboliths in all

cases except one in which one of two phleboliths demonstrated by CT was not seen on radiographs. Radiography revealed central lucency in

95 of 149 pelvic phleboliths (63%), but CT failed to depict a hypodense center in any of 150 phleboliths. The presence or absence of central

lucency on CT images cannot, therefore, be used to differentiate phleboliths from distal ureteral calculi. D 2001 Elsevier Science Inc. All

rights reserved.

Keywords: Pelvis; Radiography — pelvis; CT — veins; CT — ureter; Calculi — ureter; CT

1. Introduction

Noncontrast helical computed tomography (CT) has

recently been established as an important imaging alter-

native to KUB or excretory urography for the examination

of patients with acute flank pain and suspected ureter-

olithiasis with ureteral obstruction [1–4]. However, this

technique has a potential pitfall in the differentiation of

distal ureteral calculi from periureteral calcifications, pelvic

phleboliths in particular [3–5]. Phleboliths are calcified

concretions within a vein wall as a result of thrombosis

[6], and the incidence of them increases with age without a

statistically significant difference in incidence between

male and female [7]. Central lucency of pelvic phleboliths

is frequently found on plain pelvic radiographs [8], and

when present, it is usually considered diagnostic of a

phlebolith [5]. When it is present on noncontrast helical

CT images, pelvic phleboliths may be easily diagnosed,

with no suspicion of distal ureteral calculi. The objective

of this study was to determine the frequency with which

this phenomenon is seen on plain radiographs and non-

contrast helical CT images.

2. Materials and methods

During the past two years, noncontrast helical CT scan

was performed in our hospital in 125 patients with acute

flank pain who were suspected to have renal colic. Ninety-

three of these patients also underwent plain radiography of

abdomen and pelvis within one month of the CT scan.

Sixteen of these 93 patients had no phleboliths on plain

radiography, and in seven patients, all phleboliths were

obscured by overlying bowel loops or bony structures.

The remaining 70 patients had at least one pelvic phlebolith

that was not obscured by overlying structures, and these

patients with renal colic who underwent both abdominopel-

vic radiography obtained at 70–85 kVp and 30–40 mA and

noncontrast helical CT scanning were included in our study.

All patients were adults (38 males and 32 females) and

their ages ranged from 23 to 77 (mean, 45) years. Forty-two

patients had obstructing ureteral calculi on excretory urog-

raphy, retrograde pyelography, or noncontrast helical CT

scans, and 28 patients had no radiographic evidence of

ureteral stones or obstruction. In those patients with an

obstructing ureteral stone, all other pelvic calcifications

were presumed to represent phleboliths. In those patients

without radiographic or CT evidence of ureteral calculi or

obstruction, all pelvic calcifications were considered to

represent phleboliths.

0899-7071/01/$ – see front matter D 2001 Elsevier Science Inc. All rights reserved.

PII: S0899 -7071 (01 )00259 -5

* Tel.: +82-42-220-7835; fax: +82-42-253-0061.

E-mail address: jckim@cnuh.co.kr (J.C. Kim).

Journal of Clinical Imaging 25 (2001) 122–125

Using High Speed Advantage or Cti Standard (General

Electric Medical Systems, Milwaukee, WI) scanner, axial

CT images were obtained from the tops of both kidneys

through the base of the urinary bladder in all patients with

parameters of 120 kVp, 200–220 mA, 5-mm collimation, a

pitch of 1–1.6, and reconstruction of 5-mm intervals using a

soft-tissue setting (window width of 300–400 HU, window

level of 40–60 HU) and a bone setting (window width of

1300–1500 HU, window level of 130–150 HU).

Radiographs were interpreted together by two experi-

enced radiologists who did not know the CT findings,

and all phleboliths seen on radiography were individu-

ally identified and compared on the CT scan. With

regard to the central lucency of pelvic phleboliths, as

seen on both radiographs and CT images, two radiol-

ogists reached a consensus.

3. Results

Among the 70 patients, 150 pelvic phleboliths on

noncontrast helical CT images and 149 phleboliths on

pelvic radiographs were found. Comparison of plain

radiography and noncontrast helical CT on detected num-

ber and central lucency of these pelvic phleboliths was

summarized in Table 1.

In all cases except one, pelvic radiography and non-

contrast helical CT revealed the same number of phlebo-

liths. The exception was a case in which one of two

phleboliths demonstrated by CT was not seen on radio-

graphs (Fig. 1). The number of phleboliths per patient

ranged from 1 to 4 (mean, 2), and the largest diameter of

phleboliths varied from 3 to 7 mm (mean, 3.5 mm). There

was no sexual difference in mean phlebolith size. The total

Table 1

Comparison of plain radiography and noncontrast helical CT on detected

number and central lucency of 150 pelvic phleboliths in 70 patients

Radiography CT

Detected number of phleboliths 149 150

Central lucency of phleboliths 95 (64%) 0

Fig. 1. A 39-year-old man with right flank pain. (A) Pelvis radiograph

shows a single phlebolith of 5 mm in diameter with central lucency in right

pelvis (thick arrow). (B) Pelvis CT scan obtained using soft-tissue window

setting shows a phlebolith of 5 mm in diameter in right pelvis (thick arrow)

and another small phlebolith in left pelvis (thin arrow). Both phleboliths

have no evidence of central lucency.

Fig. 2. A 48-year-old man with right flank pain. (A) Pelvis radiograph

shows a single phlebolith of 3 mm in diameter with central lucency in right

pelvis (arrow). (B) Pelvis CT scan obtained using bone setting shows a

phlebolith of 3 mm in diameter with no evidence of central lucency in right

pelvis (arrow).

J.C. Kim / Journal of Clinical Imaging 25 (2001) 122–125 123

number of phleboliths present increased with the age of

the patient.

Pelvic radiography revealed central lucency in 95 (64%)

of 149 pelvic phleboliths (Figs. 1 and 2) and homogeneous

radiopaque or nonradiolucent center in 43 (29%) phleboliths

(Fig. 3). The remaining 11 phleboliths (7%) were too small

to be evaluated in detail.

Noncontrast helical CT on both soft-tissue and bone

setting failed to depict a hypodense center in any of 150

pelvic phleboliths (Figs. 1–3).

4. Discussion

When radiographic images show any pelvic calcifica-

tions in patients with acute flank pain, it is usually

necessary to differentiate pelvic phleboliths from distal

ureteral calculi, appendicoliths, etc. [5]. Because ureteral

calculi are frequently confused with pelvic phleboliths,

urographic imaging such as excretory urography is usually

required for the differential diagnosis of the two. Non-

contrast helical CT has been reported to be a sensitive and

accurate modality to evaluate acute flank pain and suspi-

cious ureteral calculi [1–4,6]. When ureteral dilatation is

absent or when the exact course of the ureter cannot be

determined with confidence, such as in patients with little

retroperitoneal fat, the diagnosis of ureterolithiasis can be

very difficult [6]. Ureteral calculi can be easily diagnosed

if the calcifications are located within the lumen of the

ureter or at the vesicoureteral junction, especially when the

ureter is dilated. The secondary signs of ureterolithiasis

include ureteral dilatation, nephromegaly, and perirenal

edema (stranding of the perirenal fat, perirenal fluid

collection, and thickening of the renal fascia) [9]. Tissue

rim sign (a halo of soft-tissue attenuation around a calci-

fication or the edematous wall of the ureter around the

calculus) is known to be very specific for ureteral calculi

rather than for phleboliths [10,11]. This tissue rim has

some limitations, because it may not be apparent in

patients with nonobstructing ureteral calculi or it may be

still present in patients with recently passed ureteral

calculi. Boridy et al. [6] suggested that the tail sign might

also be helpful in distinguishing phleboliths from ureteral

calculi, because the tail of soft tissue was thought to

represent the vein, venules, or venous plexus in which

the phlebolith was located.

On KUB or pelvic radiographs, it is well known that

pelvic phleboliths often have a characteristic radiolucent

center [8]. The CT appearance of phleboliths has been of

interest recently because confusion of pelvic phleboliths

with distal ureteral calculi on routine noncontrast helical CT

is now an important issue [11]. As far as we know, there is

only one report of Traubici et al. [5] to determine whether

the radiolucent center of pelvic phleboliths seen on radio-

graphs is revealed on routine unenhanced helical CT. If the

central lucency of pelvic phleboliths is also easily seen on

routine noncontrast helical CT, it may be very useful in the

difficult differentiation of pelvic phleboliths from distal

ureteral calculi on plain pelvic radiographs. In our study,

the radiographic appearance of phleboliths was compared

and correlated with their appearance on routine noncontrast

helical CT scans.

Traubici et al. [5] reported that 69 (66%) of 120

pelvic phleboliths revealed radiolucent centers on

abdominal radiography, and 119 (99%) of 120 phleboliths

failed to reveal a low-attenuation center on routine

clinical CT examinations. In our study, radiography

revealed central lucency in 95 of 149 pelvic phleboliths

(64%), but CT failed to depict a hypodense center in any

of 150 phleboliths.

We do not know the exact reason why pelvic phleboliths

lack central lucency on CT examinations despite their

appearance on radiography. Microscopic and chemical anal-

ysis of 20 phleboliths performed by Culligan [12] showed a

small central ‘‘nucleus’’ surrounded by concentric lamina-

Fig. 3. A 42-year-old woman with left flank pain. (A) Pelvis radiograph

shows a radiopaque phlebolith of 3 mm in diameter without central

lucency in right pelvis (thick arrow) and another small nodule in left

pelvis (thin arrow). The latter was considered as bowel content because

it was not radiopaque as adjacent bone and it was not shown on CT

scan. (B) Pelvis CT scan obtained using bone setting shows a phlebolith

of 3 mm in diameter with no evidence of central lucency in right pelvis

(thick arrow).

J.C. Kim / Journal of Clinical Imaging 25 (2001) 122–125124

tions. In his study, the chemical composition of the phlebo-

liths was largely calcium, magnesium, and iron in the form

of carbonates and phosphates, and small phleboliths of less

than 4 mm in diameter contained very little calcium [12]. If

a phlebolith has a somewhat elongated oval shape oriented

in the axial plane and if its center contains less calcium than

its outer portion, it might appear to have central lucency on

radiograph but not on an axial CT section [5]. At the higher

kilovoltage settings usually used for CT (120–140 kVp), X-

ray photon interactions are essentially Compton scattering,

while at the lower kilovoltage settings usually used for

radiography (60–85 kVp), there is still significant photo-

electric interactions. This may play a role in the failure to

see central lucency in phleboliths on CT scans [5].

Our study has some limitations that routine noncontrast

helical CT studies were performed with a thick 5-mm

collimation and with no overlapping reconstruction interval.

If CT scan is obtained with thinner sections of 1- or 2-mm

and overlapping reconstruction intervals, central lucency of

pelvic phleboliths on dedicated noncontrast helical CT

might be apparent.

In conclusion, central lucency of pelvic phleboliths, as

frequently seen on plain pelvic radiographs, was not

revealed by routine noncontrast helical CT in any patient.

The presence or absence of central lucency on these CT

images cannot, therefore, be used to differentiate phleboliths

from distal ureteral calculi.

References

[1] Dalrymple NC, Verga M, Anderson KR, Bove P, Covey AM, Rosen-

field A, Smith RC. The value of unenhanced helical CT in the man-

agement of patients with acute flank pain. J Urol 1998;159:735–40.

[2] Smith RC, Verga M, McCarthy S, Rosenfield AT. Diagnosis of acute

flank pain: value of unenhanced helical CT. AJR, Am J Roentgenol

1998;159:735–40.

[3] Sommer FG, Jeffery RB, Rubin GD, Napel S, Rimmer SA, Benford J,

Harter PM. Detection of ureteral calculi in patients with suspected

renal colic: value of reformatted noncontrast helical CT. AJR, Am J

Roentgenol 1995;165:509–13.

[4] Smith RC, Rosenfield AT, Choe KA, Essenmache KR, Verga M,

Glickman M, Lange RC. Acute flank pain: comparison of non-con-

trast-enhanced CT and intravenous urography. Radiology 1995;194:

789–94.

[5] Traubici J, Neitlich JD, Smith RC. Distinguishing pelvic phleboliths

from distal ureteral stones on routine unenhanced helical CT: is there a

radiolucent center? AJR, Am J Roentgenol 1999;172:13–7.

[6] Boridy IC, Nikolaidis P, Kawashima A, Goldman SM, Sandler CM.

Ureterolithiasis: value of the tail sign in differentiating phleboliths

from ureteral calculi at nonenhanced helical CT. Radiology 1999;

211:619–21.

[7] Green M, Thomas ML. The prevalence of pelvic phleboliths in rela-

tion to age, sex, and urinary tract infections. Clin Radiol 1972;

23:492–4.

[8] Rice RP. The plain film of the abdomen. In: Taveras JM, Ferrucci JT,

editors. Radiologic diagnosis-imaging-intervention, vol. 4. Philadel-

phia: Lippincott, 1992. p. 5.

[9] Katz DS, Lane MJ, Sommer FG. Unenhanced helical CT of ureteral

stones: incidence of associated urinary tract findings. AJR, Am J

Roentgenol 1996;166:1319–22.

[10] Kawashima A, Sandler CM, Boridy IC, Takahshi N, Benson GS,

Goldman SM. Unenhanced helical CT of ureterolithiasis: value of

tissue rim sign. AJR, Am J Roentgenol 1997;168:997–1000.

[11] Heneghan JP, Darlymple NC, Verga M, Rosenfield AT, Smith RC.

Soft tissue ‘‘rim’’ sign in the diagnosis of ureteral calculi with use

of unenhanced helical CT. Radiology 1997;202:701–11.

[12] Culligan JM. Phleboliths. J Urol 1925;15:175–88.

J.C. Kim / Journal of Clinical Imaging 25 (2001) 122–125 125