Keywords
18Fluorine-fluorodeoxyglucose - mucinous neoplasm - positron emission tomography/computed
tomography - urachal adenocarcinoma
Introduction
Urachal cancer is a rare clinical entity usually identified as a midline, supravesical
mass, with mixed solid-cystic components that may be difficult to confidently diagnose
from other benign urachal pathology or more commonly encountered urothelial bladder
neoplasms. Adenocarcinoma accounts for up to 80% of urachal tumors with over two-thirds
producing mucin. On computed tomography (CT), urachal adenocarcinoma can demonstrate
low-attenuation due to mucinous or necrotic components. Intrinsic calcification can
be seen in the majority of cases with solid tumor demonstrating variable enhancement
on postintravenous contrast imaging. On magnetic resonance imaging (MRI), solid components
of urachal adenocarcinoma exhibit intermediate T2 signal with the presence of hyperintense
T2 signal suggesting necrotic constituent, high mucin content, or cystic change.
Case Report
A 37-year-old woman with a history of the right invasive ductal breast carcinoma surgically
managed with right mastectomy and axillary lymph node dissection presented for follow-up.
Laboratory hematological and serum biochemical analyses were unremarkable. 18Fluorine-fluorodeoxyglucose
(18F-FDG) positron emission tomography (PET) CT was performed for the purpose of restaging.
No hypermetabolic disease was demonstrated, however, a calcified, non-FDG-avid pelvic
lesion was revealed, possibly representing a subserosal pedunculated partially calcified
uterine leiomyoma [Figure 1]. Following multidisciplinary discussion, further cross-sectional imaging was considered.
Figure 1 Sagittal positron emission tomography (a) and computed tomography (b) images, coronal
positron emission tomography (c) and computed tomography (d) images, as well as axial
positron emission tomography (e) and computed tomography (f) images, demonstrate a
well-defined soft-tissue density (arrows) in the midline pelvis, superior to the bladder,
exhibiting coarse central and peripheral calcification, and without abnormal fluorodeoxyglucose
avidity
Subsequently performed pelvic MRI demonstrated a well-defined, multilobulated, predominantly
T2 hyperintense mass arising from the anterosuperior bladder dome, extending into
the space of Retzius suspicious for a primary mucinous neoplasm [Figure 2]. Percutaneous CT-guided biopsy of the mass was performed. Histopathology showed
the presence of invasive adenocarcinoma with mucinous features invading into the lamina
propria with no evidence of urothelial component consistent with urachal mucinous
adenocarcinoma. Immunohistochemistry was positive for CK7 and CK20 and negative for
GATA3.
Figure 2 Sagittal (a) and axial (b) T2 weighted magnetic resonance imaging of the pelvis demonstrating
a lobulated supravesical lesion (arrows) with heterogeneous hyperintense signal abnormality
representing mucin
The partial bladder dome cystectomy and excision of the urachus and umbilicus were
performed. The final Sheldon stage was T3N0.
Discussion
The urachus is a fibrous cord extending from the anterosuperior bladder dome to umbilicus
that obliterates during normal fetal development. Incomplete obliteration of this
channel can result in persistent urachal pathology. Urachal adenocarcinoma, a rare
nonurothelial tumor accounting for <0.5% of bladder cancers, can develop in this vestigial
remnant and occurs almost twice as common in men with a median age of onset between
45 and 56 years.[1],[2] Urachal adenocarcinoma can present with nonspecific lower urinary tract symptoms
with almost 30% of patients present with locally advanced or distant metastatic disease
at the time of the initial investigation.[2],[3]
The current series have demonstrated a 10-year survival rate of up to 49% with surgical
treatment. Salvage chemotherapeutic agents are rarely effective with a <10% success
rate for patients with systemic metastases, which occur most commonly in the liver
and lung.[1],[2],[3]
Urachal remnant pathology demonstrates a characteristic location in the midline, superior
to the bladder dome, extending into Retzius space toward the umbilicus. On CT, urachal
adenocarcinoma usually exhibits central or peripheral calcifications, seen in up to
70% of cases. Urachal cancer may contain both solid and cystic components, demonstrating
low attenuation and heterogeneous enhancement on postcontrast imaging. Potentially
mimicking other benign and malignant pelvic pathology.[2],[3],[4],[5]
Notably, the majority (69%) of urachal adenocarcinomas are mucin-producing.[2],[5] Although FDG PET/CT may be helpful in diagnosing urachal adenocarcinoma,[6],[7],[8] it is important to highlight that up to 59% of mucinous malignancies demonstrate
low FDG avidity because of tumor hypocellularity compared to other nonmucinous tumor
types, which may limit the diagnostic efficacy of FDG PET/CT.[9],[10]
This case highlights the challenge of differentiating mucinous urachal neoplasms from
other benign low-FDG avid pelvic pathology on FDG PET/CT.
Physicians and PET readers should be aware of the limitations of FDG PET/CT in detecting
mucinous tumors and consider further evaluation of non-FDG avid calcified pelvic pathology
with additional cross-sectional imaging, such as MRI, to address the possibility of
mucinous malignancy.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms.
In the form the patient(s) has/have given his/her/their consent for his/her/their
images and other clinical information to be reported in the journal. The patients
understand that their names and initials will not be published and due efforts will
be made to conceal their identity, but anonymity cannot be guaranteed.
