Nabothian cysts (also called mucinous retention cysts or epithelial cysts) are a common and benign gynecological condition in reproductive age without clinical significance. These cysts are at the squamocolumnar junction (SCJ) of the uterine cervix, which is the targeted anatomical area of brush sampling at the time of cervical screening cytology. They are filled with mucus, but they may also contain proteinaceous material, neutrophils, or neutrophil debris. These cysts usually appear superficially and are easily recognized during colposcopy examination.
Multiple and large cysts, situated in the cervical stroma, can induce considerable enlargement of the cervix, which can lead to symptomatology. Other causes of these large cysts include cystic degeneration of uterine leiomyoma and congenital uterine cysts such as mesonephric and paramesonephric cysts and cystic adenomyosis.
The squamous epithelium of the uterine cervix proliferates, covering the columnar epithelium of the endocervical glands; this takes place when it gets chronically inflamed as a result of the healing process of chronic cervicitis, or as part of the physiological metaplasia. The columnar epithelium secrets mucous, which then forms retention cysts, which are the Nabothian cysts. Although the cysts are often small, only a few millimeters in diameter, they sometimes may reach 4 cm or more.
The epidemiology of Nabothian cysts has not been a study topic in the literature. Yet, a study was conducted in Florida hospital, USA, between 2010 and 2011 to investigate the spectrum of pigmented uterine cervix lesion over 2118 hysterectomy specimens. Researchers found the incidence of hemorrhagic Nabothian cyst to be 3%.
Nabothian cysts can occur as a result of the accumulation of secretions due to obstruction caused by trauma or inflammation.
During smear taking, superficial Nabothian cysts may get busted by the spatula; the mucoid content could stick to the brush and be smeared upon the slides in conventional cytology or be mixed in with the preserving solution of the liquid-based cytology (LBC) preparations. In LBC, mucus is rarely present, as it dissolves in the preserving solutions and centrifugation preceding the slide preparation. Macroscopically, a Nabothian cyst would appear as a cervical cyst containing mucinous liquid (2). Infrequently, mucus contained in Nabothian cysts may become impregnated by neutrophils, where its granular appearance will be visible on LBC slides. It is a well-established fact that Nabothian cyst content is identifiable on conventional Pap smears and that it can be misguided for tumor diathesis pattern that is associated with invasive carcinoma.
Microscopically, Nabothian cysts are lined by a single layer of columnar epithelium or flattened epithelium without cellular mitosis or atypia.
Nabothian cysts are often asymptomatic and discovered incidentally during colposcopy examination. However, if the cyst is large and complex, it may be mistaken for malignancy or a tumor, as it may cause symptoms such as dyspareunia, pelvic pain, pressure symptoms if it does press on an organ, for example, if it presses on the rectum it may lead to abnormal defecation and tenesmus, urinary retention, amenorrhea, and lower abdominal pain.
Transvaginal ultrasound and Magnetic Resonance Imaging (MRI) can help establish a diagnosis of Nabothian cysts. MRI can differentiate between endophytic and exophytic growth, and between normal and abnormal conditions. The Nabothian cyst appears characteristically as high T2 signal intensity on MRI.
If cancer is suspected and MRI can't exclude it, biopsy, conization, and endocervical curettage are efficient investigative tools to be used.
Sadly, despite the use of these modern diagnostic techniques, exploratory laparotomy and hysterectomy may still be required in the case of uncommonly large and deep intracervical cysts when malignancy cannot be ruled out.
Nabothian cysts require no treatment if they are asymptomatic and carry no malignant possibility. Therapy is advocated in symptomatic cases with pain, or when malignancy cannot be excluded. If required, treatment mainly consists of drainage. The main objection to surgical intervention is the risk of scar tissue, which itself may cause pain in the future.
In cases of an obstructed passage of labor, simple drainage is also used to allow normal vaginal delivery. If the diagnosis can't be reached, or in cases of deep cysts or large symptomatic cysts, excision is demanded to evaluate the histopathology and exclude other cervical tumors and adenoma malignum.
Adenoma malignum (which is a slight aberration adenocarcinoma of mucinous type, a well-differentiated multicystic form) and glandular malignant cervical lesions may mimic Nabothian cysts; however, the glandular malignant cervical lesions are usually located deep in the cervix. Also, endocervical adenocarcinoma should be a consideration, as it may present with a prominent cystic component.
Other differentials include leiomyomas, endometriosis, micro-glandular hyperplasia, squamous papilloma, and mesonephric duct remnants, all of which are benign tumors of the uterine cervix.
Trials evaluating nabothian cysts mainly focus on best detection techniques, despite multiple randomized trials that evaluate diagnostic techniques, no true gold-standard still exists.
Complications of Nabothian cysts include hematometra, labor passage obstruction, rectal compression, abnormal uterine bleeding, specifically in case of giant cysts, and chronic urinary retention by restricting the bladder's outlet or by compressing the pudendal and sacral nerves, thus, disturbing the nerve supply to the detrusor muscle.
Furthermore, during whole-body scan studies using the uptake of iodine -131, Nabothian cysts were found to be a very common cause of false-positive iodine uptake in the uterine cervix. In such cases, MRI can be used to identify the Nabothian cysts.
Even though Nabothian cysts are benign and common gynecological findings, they may present as a giant mass. If it is large and deeply located, total excision is mandatory to exclude malignancy.
As a proper preoperative diagnosis and management of cervical proliferative disorders presenting with multiple cysts, such as Nabothian cyst, have not yet been thoroughly set. A study conducted in Japan proposed a management protocol that includes a diagnostic approach by cytology, MRI, gastric-type mucin, subsequent treatment, and follow up. The usefulness of this protocol had an evaluation with 94 patients with multicystic cervical lesions between 1995 and 2014. Using the protocol mentioned above, the diagnosis was correct in 90% of the cases, and the study concluded that the proposed protocol was accurate and useful in diagnosing and treating cervical multicystic lesions.
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