A Gigantic Heterogenous Silent Corticotroph Pituitary Neuroendocrine Tumour With Posterior Fossa Cyst and a Fibrotic Wall—Diagnostic Mimicry and Route-Tailored Staging: A Case Report

The human brain is encased in a rigid skull, a protective shell that leaves little room for error when something grows inside. Within this tight space, the pituitary gland sits at the base, a small but vital organ often called the master gland because it controls the body's hormone system. Occasionally, this gland develops a tumor, a mass of cells that grows where it should not. Most of these tumors are benign, meaning they do not spread to other parts of the body, but their location can make them dangerous. If a tumor grows large enough, it can press against the optic nerves, causing blindness, or push against the brainstem, which controls breathing and heart rate. Doctors have long known that some of these tumors are "silent," meaning they do not produce excess hormones that cause obvious symptoms like weight gain or rapid growth, yet they can still be aggressive and invasive, burrowing into nearby blood vessels and bone. Treating them requires a delicate balance: removing the threat without damaging the critical structures nearby, a challenge that often demands more than one surgical approach.

This story begins with a twenty-one-year-old man who arrived at a hospital in London with a headache, double vision, and a drooping eyelid. He also had a history of autism spectrum disorder, which meant the medical team had to adapt their communication and care plan to ensure he felt safe and understood. Scans of his head revealed a massive, complex problem. A large, mixed-texture tumor had grown from the pituitary gland, filling the space behind the eyes and pressing into the cavernous sinus, a region packed with major blood vessels. Even more unusually, the tumor was connected to a fluid-filled cyst located at the very back of the brain, in an area called the posterior fossa. This cyst was so large it was squashing the brainstem, the vital stalk that connects the brain to the spinal cord. The patient's hormone levels were normal, suggesting the tumor was one of the "silent" type, but the physical pressure it created was severe.

The medical team decided to tackle the problem in stages, starting with the most accessible part. They chose an endoscopic endonasal approach, a technique where surgeons operate through the nose using a thin camera and tiny instruments. This route allowed them to reach the center of the tumor without cutting through the skull. They successfully removed the central portion of the mass, which relieved the pressure on the optic nerves and provided a tissue sample for analysis. The pathology report confirmed the diagnosis: a silent corticotroph pituitary neuroendocrine tumor. This is a specific type of tumor that produces a hormone called adrenocorticotropic hormone but does not cause the typical symptoms of hormone excess. While the central part of the tumor was gone, the team had to leave the lateral parts alone because they were wrapped tightly around the internal carotid artery, a major blood vessel. Removing that tissue through the nose would have been too risky.

In the weeks following the first surgery, the patient developed a temporary condition called diabetes insipidus, where the body struggles to regulate water, but this was managed with medication. However, a new problem emerged. The fluid-filled cyst at the back of the brain, which had been compressed by the tumor, began to grow again. It expanded rapidly, pushing against the brainstem and causing the patient to develop trouble walking and speaking. The fluid buildup also caused hydrocephalus, a condition where cerebrospinal fluid accumulates in the brain. The team first tried a minimally invasive solution: they attempted to insert a small catheter into the cyst through the skull to drain the fluid. This device, known as an Ommaya reservoir, is often used for cysts with thin, flexible walls. But in this case, the cyst wall was tough and fibrous, like a thick, rubbery membrane. The catheter bounced off the wall twice, unable to penetrate it, and the drainage attempt failed.

Recognizing that the minimally invasive route was not working, the team switched strategies. They performed an open craniotomy, a traditional surgery where a section of the skull is temporarily removed to access the brain directly. This approach allowed them to see the cyst clearly and cut through the tough, fibrous wall under direct vision. They successfully drained the fluid and removed more of the tumor from the side, relieving the pressure on the brainstem. The patient's ability to walk and speak improved significantly after this operation. Despite the success, some of the tumor remained near the blood vessels, where further surgery would have been too dangerous. To handle this remaining tissue, the patient received proton beam therapy, a highly precise form of radiation that delivers energy to the tumor while sparing the surrounding healthy brain tissue. He received a total dose of 50.4 Gy over twenty-eight sessions.

The outcome was a clear demonstration of how complex brain tumors sometimes require a tailored, multi-step plan. The initial surgery through the nose secured the diagnosis and protected the vision. When the cyst proved too tough for a needle, the team did not persist with a failing method; instead, they moved to an open approach to solve the immediate life-threatening pressure. Finally, radiation therapy was used to control the parts of the tumor that could not be safely removed. Follow-up scans showed that the remaining mass had shrunk, and the patient's neurological function continued to improve. The case highlights that for certain aggressive, silent tumors, a single surgical route is often not enough. Success depends on recognizing when a minimally invasive technique has reached its limit and having the flexibility to switch to a more direct approach, all while using advanced radiation to ensure long-term control. The patient's journey underscores the importance of a coordinated team that can adapt its strategy to the unique biology of the tumor and the specific needs of the individual.