In-utero Diagnosis of Prostatic Embryonal Rhabdomyosarcoma

Introduction

Rhabdomyosarcoma is the most common soft-tissue tumor in children, causing 3–5% of all pediatric malignancies with a median age at diagnosis of 5–6 years.¹ The most common subtype, embryonal rhabdomyosarcoma, most commonly effects the head and neck and genitourinary structures. Some studies report that approximately 13–20% of pediatric rhabdomyosarcoma cases arise from genitourinary organs including the bladder, prostate, and the uterus². Here, we present a case of prenatally detected prostatic embryonal rhabdomyosarcoma and it’s postnatal evaluation in a newborn patient. A literature reviewed revealed no reported cases of prenatally detected prostatic embryonal rhabdomyosarcoma.

Case Report

A 35-year-old G2P1 woman with no obstetric complications presented for prenatal ultrasound at 33 weeks 6 days gestation. The study demonstrated a solid mass at the base of the fetal bladder (Fig. 1). The prenatal ultrasound was otherwise normal. After a full-term uncomplicated birth, labot, and delivery, a postnatal ultrasound revealed a 2.2 × 1.5 cm pedunculated, vascular mass at the base of the bladder with normal appearance of the ureters and kidneys (Fig. 2A). The patient was referred to our pediatric urology clinic for further evaluation where he had no urinary symptoms and physical examination was unremarkable.

Figure 1:

Prenatal Ultrasound at 33 weeks 6 days Gestation

Solid mass in the inferior fetal bladder measuring 1.14 cm × 1.09 cm.

Figure 2:

Postnatal Imaging

A) Postnatal ultrasound demonstrating a 2.2 × 1.5 cm mass within the bladder.

B) MRI of abdomen and pelvis at 33 days old. Slightly T2 hyperintense 0.9 × 1.4 × 2.5 cm (AP x TV x CC) mass centered in the posterior urethra/prostate that extends into the inferior urinary bladder.

C) VCUG at 37 days old. (Left) Persistent filling defect in the inferior urinary bladder during the early filling phase. (Right) Markedly posterior urethral dilatation which intermittently opacifies with contrast over the course of the examination.

At 33 days old, multiplanar T1-weighted, T2-weighted, and diffusion-weighted MRI sequences were obtained of the abdomen and pelvis, including dynamic post-contrast T1-weighted sequences (Fig. 2B). MRI demonstrated a 0.9 × 1.4 × 2.5 cm T2 hyperintense mass centered in the posterior urethra/prostate that extended into the inferior urinary bladder. The mass did not extend outside of the bladder/prostate and there was no detectable lymphadenopathy.

Follow-up voiding cystourethrogram (VCUG) on day of life 37 revealed a persistent filling defect in the inferior urinary bladder seen during the early filling phase (Fig. 2C). The posterior urethra was markedly dilated and intermittently opacified with contrast over the course of the examination. The posterior urethra appeared to dilate as the mobile mass transits to the posterior urethral lumen from the urinary bladder. The patient produced a subjectively strong urinary stream per urethra throughout VCUG examination. Imaging of the renal beds obtained during voiding and oblique views of the ureterovesical junctions did not show evidence of reflux.

At 45 days old, the patient underwent cystoscopy with transurethral mass biopsy. During the procedure, the distal urethra appeared normal. Proximal to the verumontanum, there was soft fluffy type of tissue in the region of the prostate that extended into the urinary bladder (Fig. 3A). The tissue was biopsied using a 9.5 loop resectoscope. Biopsy of the mass was consistent with embryonal rhabdomyosarcoma, with a confirmatory immunohistochemical phenotype. Subsequent molecular evaluation documented lack of FOX01 fusion, compatible with the embryonal subtype of rhabdomyosarcoma (Fig. 3B). Staging studies showed no other sites of disease. The patient was staged as Stage 2, Group III (intermediate risk). Following an extensive discussion of the range of surgical options, including upfront cysto-prostatectomy (which would have rendered him Stage 1, Group I, low-risk and have resulted in the need for a substantially shorter and less intensive chemotherapy treatment regimen), the family opted to proceed without additional surgery and the patient began standard-of-care treatment with alternating cycles of Vincristine, Dactinomycin, and Cyclophosphamide (VAC) and Vincristine and Irinotecan (VI). Repeat imaging after 3 months of treatment showed no change in the size of the mass. The patient remains on chemotherapy with plans to avoid surgery and radiation therapy in the absence of disease progression.

Figure 3:

Gross and histology appearance of mass

A) Gross appearance of mass on cystoscopy

B)The biopsy showed a mildly hypocellular tumor within a loose myxoid stroma. The tumor was composed of rounded and spindled cells containing a variable amount of eosinophilic cytoplasm. Occasional strap cells consistent with skeletal muscle differentiation were seen (arrows). The urothelium could be seen at the top of the biopsy but was compressed by the underlying tumor. (Hematoxylin and eosin stain; 200x)

Discussion

Here, we report a case of prenatally detected prostatic embryonal rhabdomyosarcoma diagnosed at 33 weeks 6 days gestation. This finding was worked up with postnatal ultrasound, MRI, and VCUG with subsequent biopsy confirming prostatic embryonal rhabdomyosarcoma.

Imaging was a key factor in identifying a mass in this patient. Imaging allows practitioners the ability to assess the primary tumor, its extent, and plays a role in long term follow up of these patients.¹ Previous studies report the use of ultrasound to aid in the diagnosis, but these are often done in postnatal setting. Due to improvements in prenatal imaging, there has been an increase in detection of tumors on prenatal ultrasound. There are only a handful of published reports describing prenatally detected embryonal rhabdomyosarcoma. These were located in the thoracic cavity, orbits, cervix, and extremities.^3–7 The management of prenatally diagnosed lesions is complex and often requires a multidisciplinary team. One study found that the involvement of pediatric surgical specialists led to 3.4% change in the decision to terminate pregnancy based on information about the diagnosis and potential prognosis.⁸

Prenatal ultrasound plays a large role in detecting abnormalities within the genitourinary tract. The fetal kidneys and bladder can be seen around 10–12 weeks of gestation.⁹ The prostate is difficult to image in the prenatal setting. Postnatally, magnetic resonance imaging (MRI) proved very useful in identifying this mass, as well as its origin and extension. The goal of MRI is to characterize the primary tumor with rhabdomyosarcoma showing intermediate signal intensity on T1-weighted images and intermediate to high signal intensity on T2-weighted images.¹

The disease has a bimodal age distribution that peaks in the first 2 years of life followed by another peak during adolescence. Within the literature there are 2 reported cases of the diagnosis being made within the first 6 months of life.^10,11 In both cases the children were treated with upfront vincristine, actinomycin, and cyclophosphamide therapy followed by surgical management with cystectomy and urinary diversion.^10,11 In this instance, based on the favorable prognosis for long-term survival associated with a conservative approach to surgery, and the desire to avoid the devastating effects of pelvic radiation in an infant, a chemotherapy-alone approach was recommended^12,13. After three months of chemotherapy, the child’s tumor remains apparently controlled with treatment ongoing.