Incidentally detected grade 3 cystocele on FDG PET/CT in a case of suspected malignancy.

Unexpected findings are seen on FDG PET/CT outside the primary site of abnormality. Such incidental findings are common in the genitourinary tract due to normal urinary excretion of FDG. We report a case of incidentally detected grade 3 cystocele in a patient who underwent FDG PET/CT study for a suspected lung malignancy.

INTRODUCTION

Physiological sites of FDG uptake are well documented, with urinary bladder being one of these. Since it is the route of tracer excretion, any pathology related to urinary bladder is associated with FDG avidity. Grade III cystocele was incidentally seen on FDG PET/CT done for a 65 year old lady, which was identified due to a large area of tracer concentration in communication with the urinary bladder.

CASE REPORT

A 65-year-old lady presented to our institution with non resolving pneumonia. She had severe cough with expectoration since 2 months, which aggravated over last one month. She also complained of significant weight loss during that period. Posteroanterior chest radiograph showed consolidation involving the lower lobe of left lung, following which she was treated with broad spectrum antibiotics. Since there was no improvement in her symptoms and her radiographic findings, lung malignancy was suspected. She was referred for a whole body 18 Fluoride fluorodeoxyglucose positron emission tomography/computed tomography (18 F FDG PET/CT), for further evaluation of a possible malignant etiology. Maximum Intensity Projection (MIP) images revealed low grade FDG uptake in left lung [Figure 1-arrowhead], corresponding to the consolidation and ground glass opacification seen on the CT component of the study. Physiological tracer distribution was seen in the heart, brain, liver and urinary bladder. However, a distinct focus of intense FDG uptake was seen inferiorly, separate from the urinary bladder [Figure 1-arrows]. The intense nature of the FDG concentration was similar to that of urinary tracer accumulation in the bladder. Axial CT images showed that the uptake corresponded to a well defined rounded lesion, which was protruding out from the introitus and had a fluid density Figure 2-arrow]. Sagittal fused PET/CT images revealed that there was definite communication with the bladder, suggesting the possibility of herniated bladder [Figure 3-arrows]. Subsequent clinical evaluation confirmed that the intensely tracer concentrating structure at the introitus was a grade 3 cystocele.

Figure 1

MIP image showing FDG uptake in left hemithorax corresponding to lung mass (arrowhead) and two large foci of uptake in the pelvis (arrows)

Figure 2

Axial CT image showing cystocele protruding from the introitus (arrow)

Figure 3

Sagittal fused images shows tracer concentration in bladder and cystocele suggestive of definite communication (arrows)

DISCUSSION

FDG is excreted by kidneys without reabsorption by proximal tubules, as a result of which increased tracer uptake is seen in the renal collecting system, ureters, and bladder. There are occasions when urinary tracer concentration can simulate pathology resulting in false positive PET studies.[1] Commonly, tracer activity in the ureter can be focal and mimic a retroperitoneal node. Also, in patients with previous transurethral resection of prostate, urine may be retained in the dilated prostatic urethra, which passes through the midline of prostate. Also, uptake may be seen in surgical urinary diversions such as ileal conduit.[2] Intense tracer activity in the bladder is always a hindrance as it compromises the sensitivity of FDG PET for neighboring adnexal organs. The intense nature of tracer concentration in the urinary bladder normally is very suggestive and is easily recognized as physiological uptake. However, on certain occasions such as post surgery or radiation therapy the normal orientation and contours of the bladder are altered and displaced and the uptake can be falsely regarded as pathological. On such occasions the CT component of the examination proves useful in localizing the uptake.[3] Our case demonstrates one such unusual cause of bladder displacement, the location of which and its intense tracer uptake which can potentially mimic a pathology. Cystocele is protrusion of bladder into or through the vagina and is radiographically defined as descent of the bladder base below the pubococcygeal line, which defines the level of pelvic floor.[4] It is primarily caused due to weakening of pubocervical fascia due to child birth, aging or prior hysterectomy, other causes include obesity, heavy lifting and chronic constipation. The patient in our report had grade 3 cystocele as the bladder had bulged through the introitus.[4] Our case demonstrates how a commonly encountered clinical condition like cystocele can potentially mimic a sinister pathology on FDG PET scan. It also highlights how careful attention to the nature and intensity of FDG uptake and the anatomical information provided by CT can avoid potential pitfalls when FDG concentration is noted in a displaced and altered urinary system.