A rare case of subpubic parasymphyseal cyst, diagnosed with MRI imaging, in a patient with prostate cancer who underwent pelvis radiotherapy

¹Medical Physics Laboratory, School of Medicine, Democritus University of Thrace, Alexandroupolis, Greece, ²Department of Interventional Radiology, General University Hospital of Patras, Patras, Greece, ³Department of Surgery, General University Hospital of Patras, Patras, Greece, ⁴Department of Radiology, School of Medicine, Democritus University of Thrace, Alexandroupolis, Greece, ⁵Department of Radiotherapy/Oncology, School of Medicine, Democritus University of Thrace, Alexandroupolis, Greece

^&Corresponding author
Eleni Bekou, Medical Physics Laboratory, School of Medicine, Democritus University of Thrace, Alexandroupolis, Greece

Introduction    

The cartilaginous subpubic cyst is a rare cystic lesion characterized by cyst formation in the pubic symphysis area. Limited literature is available on cartilaginous subpubic cysts. Most cases are reported in multiparous and post-menopausal women [1]. Patients may report a variety of symptoms, including urinary voiding difficulties, a painless slow-growing vulvar mass, or pelvic pain and dyspareunia. There are limited reported male cases with cartilaginous subpubic cysts that usually present with discomfort or pain in the perineum, scrotum, or testicles [1,2]. Magnetic Resonance Imaging (MRI) characteristics of these cysts are crucial to pubic cysts' diagnosis and management. Still, a complete report of MRI features of parasymphyseal cysts (PD) has been described only in one female case [3]. In last, there are no studies that describe the role of pelvis radiotherapy on cartilaginous subpubic cysts.

The current study is one of the few reports focused on managing subpubic cysts in male patients including a complete review of the role of MRI imaging before and after pelvis radiotherapy.

Patient and observation     

Patient information: a 72-year-old man, with a biopsy-proven diagnosis of prostate cancer, underwent an MRI scan of the prostate for the staging of an underlying prostatic carcinoma. The patient reported excessive urinary frequency without any other specific symptomatology. Prostate Specific Antigen (PSA) serum was found to be abnormal (8 ng/ml; normal value < 4 ng/ml), while digital rectal examination was normal.

Clinical findings: MRI findings were suspicious for prostate adenocarcinoma. The detected lesion had dimensions < 1.5 cm, located in the right apex transitional zone characterized as Prostate Imaging Reporting and Data System (PI-RADS) score III. MRI-guided prostate biopsy has verified intermediate prostate risk adenocarcinoma with Gleason Score (GS)= 7 (4+3). In addition, MRI revealed an oval fibrous mass attached to the subpubic symphysis area.

Timeline: the patient came into our department for an MRI scan of the prostate cancer staging before pelvis radiotherapy. MRI findings revealed a cyst attached to the subpubic symphysis area. The patient received pelvis radiotherapy and was referred for imaging observation of the subpubic cyst.

Diagnostic assessment: the MRI findings in the subpubic symphysis area were verified with a mass measuring 1.27 cm x 1.43 cm x 1.16 cm. The lesion was hypointense about muscular tissue on T1-weighted sequences and heterogeneously hyperintense on T2-weighted sequences (Figure 1). Diffusion-weighted imaging (DWI) shows a decreased signal on a high b-value and an increased signal on a low b-value with a corresponding high Apparent Diffusion Coefficient (ADC) value on ADC maps (Figure 2).

T1-weighted DIXON without contrast enhancement corresponded to the area of decreased intensity showing a cystic component (Figure 3 A). Also, the cystic formation was confirmed from T2-weighted multi-echo fast field echo (mFFE), which did not present a blooming (Figure 3 B). Finally, the mean diffusivity and fractional anisotropy (FA) from Diffusion Tensor Imaging (DTI) revealed the water content of the cyst (Figure 4 (A,B)). Based on the MRI evidence and the location of the lesion, we considered a diagnosis of the subpubic cartilaginous cyst (SCC).

Therapeutic intervention: the patient was treated with hypo-fractionated-accelerated radiotherapy for prostate cancer and received 4.32 Gy in 7 fractions of 6.05 Gy within 24 days. The patient is encouraged to observe with imaging modalities due to the absence of a specific treatment following the existence of bibliography guidelines.

Follow-up and outcomes: the follow-up of the patient was done 2 months after completion of radiotherapy sessions. On follow-up, the patient underwent an MRI screening using the same MR protocol. The imaging finding revealed that SCC dimensions remained the same. Signal intensities of SCC on T2W, DWI, ADC, and DTI images were reduced as expected due to the effects of radiation verified the normal glandular tissue of the lesion. Also, T1 DIXON without constant enhancement and mFFE verify the cystic components of a lesion.

Patient perspective: the patient and his family were satisfied with the health care we provided during the hospitalization, and they were hopeful about his health outcomes.

Informed consent: the patient was informed about the publication of the case report and why the authors wanted to report it. A verbal consent was obtained from the patient for the clinical data to be published in the journal.

Discussion     

A cartilaginous pubic cyst, also known as a retropubic parasymphyseal cyst, is an uncommon cystic lesion of the pubic symphysis. Histopathological analysis of this cyst reveals inflammatory fibrous tissue infiltrated by lymphocytes without evidence of malignancy [1].

The pubic symphysis is a cartilaginous joint between two thin layers of hyaline cartilage of the pubis of the hip bones. Specifically, pubic symphysis is a non-synovial amphiarthrosis featuring a fibrocartilaginous disc. The absence of a synovial membrane shields the joint from synovial disorders [4]. The joint's stability is predominantly provided by a robust arcuate ligament, also known as the inferior pubic ligament, which stretches across the lower pubic branches. Although the symphysis pubis can be impacted by various conditions, including infectious, congenital, metabolic, inflammatory, traumatic, and degenerative processes, the occurrence of cysts in this location is uncommon. Based on the site of origin of the cyst from the joint cartilage, they can be suprapubic, retropubic, and subpubic in location.

The first reference to this rare mass was by Alguacil-Garcia et al. in 1996 in two female patients [5]. A similar case in a 72-year-old asymptomatic male was reported by Martel et al. in 2007 [6]. Since then, other 4 cases have been reported on male patients. Table 1 summarizes the clinical data for subpubic cartilaginous cysts in males. Because of their rarity, there is not a well-documented range of symptoms [1-7]. However, symptoms may include pain or discomfort in the pubic area or lower abdomen, pelvic pain, and even lower urinary tract symptoms if the cyst compresses the bladder or urethra [1,5,8]. However, in some cases, men may not present symptoms, and the cysts are discovered incidentally during routine imaging [6,8]. Consequently, careful assessment and follow-up are mandatory for the management of both symptomatic and asymptomatic patients with retropubic parasymphyseal cysts. Clinicians should ensure proper diagnosis and discussion for the management of the multi-disciplinary board.

Appropriate diagnostic methods, such as MRI, ultrasound (US), and computed tomography (CT) are valuable for the characterization of the component of the cyst and lesion´s location [2,6,7]. US diagnostic accuracy is restricted only to characterize the existence of a cystic structure in the symphysis pubis [1]. Computed Tomography (CT) scan of the pelvis verifies cystic masses with characteristic gas-containing masses due to containing small foci of nitrogen gas from the degenerative fibrocartilaginous disc of the symphysis pubis [1,6,8]. MRI, a non-ionizing imaging method, can also detect and characterize a cyst using conventional and advanced imaging techniques. A cartilaginous pubic cyst located on the center of pubic mass depicted hypointense on the T1 weighted and hyperintense on the T2 weighted conventional techniques [1,2,4-8]. The freedom of its molecular motion and cellulitis can be estimated through low and high b-value DWI signals, combined with the information derived from the relative quantitative ADC map. Cysts lesions do not show DWI restriction in cyst lesions and their ADC value is high [5-8].

Our case shows that T1 DIXON without constant enhancement suppressed fat or water signals may reveal the cystic components of a lesion. Also, mFFE sequences are sensitive to magnetic susceptibility differences and could distinguish the malignant from benign cysts, appearing as areas of signal drop-out. These findings verify the most results of the case of Javalgi et al. [3]. Our case highlights the importance of implementing DTI sequences which is an evolution of the DWI technique since it can quantify the molecular motion in more than one direction and provide quantitative indices useful for lesion characterization [9]. In this case, we observed high mean diffusivity and low fractional anisotropy due to the free diffusion of water within the cystic fluid, reflexed in benign cystic mass.

Retropubic parasymphyseal cysts most commonly are benign but, ultrasonography-guided needle biopsy, CT-guided aspiration of the cyst, or open biopsy must be performed to exclude malignancy [10]. Sometimes, resection may be necessary due to lesion size and urinary tract symptoms [5,10]. There is no standard treatment established for retropubic parasymphyseal cysts (RPC). Observation with imaging modalities is crucial for the management and follow-up of pubic cysts, especially in asymptomatic cases.

According to previous studies, in male patients with cysts ≤3 cm in size, the cystic lesion might shrink spontaneously after several years. Additional medical treatment may be considered, in larger than 3 cm cysts or when symptomatology persists. Cyst aspiration and instillation with steroids have been used, demonstrating a temporary reduction of the lesion.

In our study, radiation does not seem to be affected drastically on dimensions or on the structure of SCC. Laparoscopic or surgical resection seems to be more effective.

Conclusion     

Subpubic parasymphyseal cyst is a rare benign lesion in the pubic symphysis area, occurring commonly in postmenopausal women and rarely in men. Its diagnosis may be difficult due to variable pressure symptoms, mainly discovered incidentally during routine imaging. US and CT imaging have restricted diagnostic accuracy. Conventional and advanced MRI imaging techniques highlight the anatomical and functional lesion with high sensitivity and specificity of the diagnostic images. The lack of standardized treatment makes also difficult the treatment of SCC. This case report describes MRI imaging features of a parasymphyseal cyst that can be of clinical value in diagnosis and the restricted role of radiotherapy of the pelvis. Further studies are necessary to conclude the role of pelvis radiotherapy on SCC.

Competing interests     

The authors declare no competing interests.

Authors' contributions     

All the authors read and approved the final version of this manuscript.

Table and figures     

Table 1: clinical data for subpubic cartilaginous cyst in male

Figure 1: T2-weighted magnetic resonance (MR) images in axial (A); coronal (B); and sagittal (C) planes show a well-defined hyperintense lesion in the space of pubic symphysis

Figure 2: diffusion-weighted images (A) with b=0 s²/mm; (B) b=800s²/mm; (C) Apparent Diffusion Coefficient (ADC) map in axial planes show cystic lesions with no diffusion restriction

Figure 3: (A) T1-mDIXON sequence on an axial plane without contrast enhancement, the suppressed signal intensity of subcutaneous and perirectal fat reveal; (B) axial mFFE

Figure 4: the free diffusion of water within the cystic fluid created high (A) mean diffusivity and low (B) fractional anisotropy (FA) diffusion tensor imaging (DTI) images

References