A 66-year-old man presents to A&E with a 3-day history of worsening abdominal discomfort. The pain started as dull and centered around the upper abdomen but has intensified and spread throughout the abdomen. He feels bloated, experiences occasional nausea, and has a reduced appetite. 
His has osteoarthritis and atrial fibrillation, but he is otherwise fit and well.
On physical examination, he appears pale and somewhat distressed. His abdomen is distended, with diffuse tenderness and involuntary guarding. Bowel sounds are faint, and percussion elicits tympany.
Observations: blood pressure 99/56mmHg, pulse rate 101bpm, respiratory rate 18 breaths per minute, oxygen saturations 100% on room air, temperature 37.6 degrees Celsius.
An erect chest x-ray shows the following:
What is the most likely diagnosis?

Options:
explanation: Although headaches are reasonably common following a lumbar puncture, they typically resolve within 14 days of the procedure. Furthermore, they are usually worsen in an upright position and are relieved when lying down, which differs to the experience of this patient. Post-lumbar puncture headaches can occur when there is a persistent leak of cerebrospinal fluid (CSF) through the dural puncture site, causing a reduction in CSF pressure. By contrast, this vignette describes symptoms of increased intracranial pressure.
name: Furosemide treatment
label: d
answer: no
explanation: Although headaches are reasonably common following a lumbar puncture, they typically resolve within 14 days of the procedure. Furthermore, they are usually worsen in an upright position and are relieved when lying down, which differs to the experience of this patient. Post-lumbar puncture headaches can occur when there is a persistent leak of cerebrospinal fluid (CSF) through the dural puncture site, causing a reduction in CSF pressure. By contrast, this vignette describes symptoms of increased intracranial pressure.
name: Post-lumbar puncture
label: b
answer: no
explanation: This is the correct answer. The patient has a history of lung cancer, which commonly metastasises to the brain. This vignette describes symptoms of increased intracranial pressure. According to the Monro-Kellie Doctrine, cerebrospinal fluid (CSF), blood volume and brain parenchyma volume exist in equilibrium. Metastatic brain tumours typically form space-occupying lesions within the brain tissue. They increase the brain parenchyma volume, increasing the pressure inside the intracranial cavity. Brain metastases can also obstruct the flow of CSF, leading to a build-up of CSF and increased pressure within the intracranial space.
name: Intracranial metastasis
label: a
answer: yes
explanation: This vignette describes symptoms of increased intracranial pressure (ICP). By contrast, dehydration could lead to decreased ICP. According to the Monro-Kellie Doctrine, cerebrospinal fluid (CSF), blood volume and brain parenchyma volume exist in equilibrium. Severe dehydration could reduce the volume of cerebrospinal fluid within the intracranial and intraspinal spaces, which could lower ICP. Furthermore, it would be highly unusual for a dehydration headache to last for so long.
name: Dehydration
label: c
answer: no
explanation: This vignette describes symptoms of increased intracranial pressure (ICP). Cluster headaches are severe headaches that occur in clusters. They are often described as excruciating pain focused around one eye, and may be associated with other symptoms like tearing, nasal congestion, and restlessness. They are not typically worsened by lying down, and would not last for several weeks.
name: Cluster headache attacks
label: e
answer: no

Correct answer: a

Intracranial metastasis