This study reports the spontaneous resolution of a cavum septum pellucidum (CSP) cyst. While a CSP is a frequently encountered normal variant, the occurrence of a cyst within the CSP is rare. Significant debate exists regarding their clinical relevance, natural progression and their need for intervention. Even more rare is the spontaneous resolution of a CSP cyst, a phenomenon scarcely described in the literature in a handful of case reports. We provide imaging evidence demonstrating the spontaneous resolution of a CSP cyst in a patient with a history of recurrent falls with loss of consciousness (LOC).

A fifty-year-old man was referred to the neurology clinic by his primary care physician for a history of recurrent falls with LOC that started two years ago. He had around three episodes or more per month. He also had memory issues. He denied any history of headache or visual symptoms. There was no history of head injuries, central nervous system infection or febrile seizure. His past medical history was significant for diabetes, generalized anxiety disorder and osteoarthritis. On physical examination, the patient’s vitals were within normal limits, and his neurological examination was unremarkable. The blood work-up and electrocardiogram were also unremarkable. The initial head computed tomography (CT) and brain MRI were unremarkable apart from incidental finding of a CSP et cavum vergae (Figure 1 (A)–(B)). The follow up CT head obtained more than a year later demonstrated interval enlargement of the CSP diameter, associated with newly seen outward bowing of the leaflets, suggestive of an expanding cyst of the CSP (Figure 1 (C)–(D)). The repeated brain MRI after 18 months demonstrated normal size and morphology of the CSP et vergae with interval resolution of previously identified outward bowing of the leaflets, indicating spontaneous resolution of a CSP cyst (Figure 2). The CSF flow images were normal with no evidence of hydrocephalus. Despite regression of CSP cyst, patient continued to have a stable course of his nonspecific symptoms without significant improvement. He was referred to neurosurgery for further consultation to evaluate whether intermittent CSF flow impedance could be the cause of his symptoms.

Figure 1. Initial MRI brain (A) axial and, (B) coronal FLAIR MR images show cavum septum pellucidum and vergae. Follow up CT head 18 months later (C) axial and, (D) coronal CT head shows interval development of an expanding septum pellucidum cyst situated between the lateral ventricles associated with outward bowing of wall leaflets (white arrows). No associated hydrocephalus.

Figure 2. Follow up MRI brain 19 months later (A), (B), (C) axial T2, coronal T2 and axial FLAIR show normal size and morphology of cavum septum pellucidum and vergae with interval resolution of previously identified CSP cyst and outward bowing of wall leaflets.

The CSP may persist in 15% of the adult population. ^{Reference Hong, Chen, Guo and Zhang3} Although the majority of CSP cases are discovered incidentally and considered normal variants with negligible clinical significance, some studies have suggested an association between a large CSP and repetitive head trauma, as seen in boxers and individuals with certain neuropsychiatric disorders such as schizophrenia. ^{Reference Bot, Constantini and Roth4} CPS cysts are uncommon finding with estimated frequency of 0.04% in brain CT and MRI, defined as outward bowing leaflets of CSP walls and a transverse diameter exceeding 10 mm. ^{Reference Hong, Chen, Guo and Zhang3,Reference Bot, Constantini and Roth4} They are classified as either asymptomatic or symptomatic. The most common type is asymptomatic (communicating type), which communicates with the ventricular system. They are usually discovered incidentally, remain stable throughout the life and are managed conservatively. On the other hand, noncommunicating cysts, which are symptomatic, do not communicate with the ventricular system or cisternal spaces. ^{Reference Hong, Chen, Guo and Zhang3–Reference Loft, Rafaelsen and Pedersen5} The symptoms occur once the cyst is growing in size and exerting local mass effect on nearby structures and/or causing hydrocephalus. ^{Reference Hong, Chen, Guo and Zhang3,Reference Kojder7} The real mechanism behind the cyst expansion is still unknown. ^{Reference Hong, Chen, Guo and Zhang3,Reference Sagan, Limanówka, Herbowski, Poncyljusz and Giżewska8} Several hypotheses explained the mechanisms for cyst growth and enlargement, including fluid secretion within CSP by ependymal cells, ball-valve mechanisms causing progressive fluid accumulation and entrapment within CSP or osmotic gradients between the cyst and subarachnoid space. ^{Reference Hong, Chen, Guo and Zhang3,Reference Bot, Constantini and Roth4,Reference Krejčí, Krejčí and Lipina6,Reference Sagan, Limanówka, Herbowski, Poncyljusz and Giżewska8} The clinical manifestations of symptomatic cysts fall into two categories: one includes headaches, dizziness, vomiting, LOC and papilledema, due to blockage of the interventricular foramina. While the other includes behavioral, autonomic and sensorimotor symptoms, brought on by compression of the hypothalamoseptal triangle’s structures or impairment of the deep cerebral venous drainage. ^{Reference Sayama, Harnsberger and Couldwell2,Reference Hong, Chen, Guo and Zhang3,Reference Sagan, Limanówka, Herbowski, Poncyljusz and Giżewska8} But because the symptoms of septum pellucidum cysts are nonspecific, sometimes it can be difficult to tell if the cyst is the cause of the symptoms or can be attributed to another cause, like in our patient. ^{Reference Hong, Chen, Guo and Zhang3}

There are no specific guidelines or recommendations for treatment option of symptomatic cysts, and the management of these conditions is controversial. ^{Reference Kojder7,Reference Sagan, Limanówka, Herbowski, Poncyljusz and Giżewska8} The surgical intervention is recommended for large symptomatic cysts that cause obvious hydrocephalus or local compression, with different treatment options, including direct craniotomy, conventional ventriculoperitoneal shunting, stereotactic fenestration and neuroendoscopic cystoventriculostomy. ^{Reference Hong, Chen, Guo and Zhang3,Reference Kojder7,Reference Sagan, Limanówka, Herbowski, Poncyljusz and Giżewska8} The neuroendoscopic treatment is considered to be a safe and efficient method with immediate symptomatic relief and fewer complication compared to other alternatives. ^{Reference Kojder7,Reference Sagan, Limanówka, Herbowski, Poncyljusz and Giżewska8} Only a few cases of CSP cysts have been reported to resolve spontaneously without surgical intervention. ^{Reference Koçer, Kantarci, Mihmalli, Işlak and Cokyüksel1–Reference Krejčí, Krejčí and Lipina6} In 2000, Kocer et al reported the first case of spontaneous resolution of an asymptomatic cyst of the septum pellucidum. ^{Reference Koçer, Kantarci, Mihmalli, Işlak and Cokyüksel1} Spontaneous fenestration of the cyst secondary to increased pressure or shear forces on an area of thinning out lateral wall seen on follow up MRI was suggested as the mechanism of cyst resolution. ^{Reference Koçer, Kantarci, Mihmalli, Işlak and Cokyüksel1,Reference Hong, Chen, Guo and Zhang3} Previous literature suggested spontaneous cyst regression attributed to mechanisms such as intracystic pressure changes or micro-fenestrations of the cyst wall. ^{Reference Koçer, Kantarci, Mihmalli, Işlak and Cokyüksel1,Reference Sayama, Harnsberger and Couldwell2} Straining, coughing, breath holding, forced breathing, swimming, sports and head trauma are some of the factors that can cause profound shear forces and elevated intracystic pressure. ^{Reference Hong, Chen, Guo and Zhang3} Other processes that might contribute to spontaneous cyst regression include the reabsorption of the cyst by capillaries and veins in the septal wall and the displacement of fluid from the cystic cavity into the ventricle by a pressure gradient. ^{Reference Hong, Chen, Guo and Zhang3–Reference Loft, Rafaelsen and Pedersen5} In the present case, no direct evidence of fenestration or trauma was observed, suggesting that other factors may contribute to cyst regression.

Finally, we present a case of a large CSP cyst that resolved spontaneously. We propose that the lack of regular monitoring and follow-up of patients with a CSP cyst may result in underestimation of the frequency of spontaneous cyst regression. Spontaneous resolution, though rare, may occur, and a conservative approach should be considered in treatment planning, particularly when hydrocephalus or neurological deficits are absent, to avoid unnecessary surgical interventions. Close follow-up with imaging remains essential to ensure favorable outcomes.