A 52-year-old man from Delhi presents with a 3-month history of progressive left-sided weakness and sensory loss in a pyramidal distribution. MRI brain shows a well-defined, T2-hyperintense mass in the right motor cortex with minimal surrounding edema and no enhancement on contrast-enhanced T1. Diffusion-weighted imaging shows no restricted diffusion. There is no mass effect or midline shift. What is the most likely diagnosis?

Explanation

## Imaging Diagnosis of Cavernous Malformation **Key Point:** Cavernous malformations (cavernomas) are characterized by the pathognomonic "popcorn" appearance on MRI — a lesion with mixed signal intensity (hemosiderin-containing caverns of varying ages) surrounded by a hemosiderin rim on gradient-echo sequences, with minimal or absent enhancement. **High-Yield:** The classic MRI triad of cavernous malformation: 1. **No enhancement** or minimal enhancement (unlike gliomas) 2. **Hemosiderin rim** (hypointense on T2/GRE) — pathognomonic 3. **Mixed internal signal** (T2-hyperintense with hypointense foci) from recurrent microhemorrhages 4. **Minimal vasogenic edema** (unlike tumors) ### Pathophysiology and Clinical Presentation Cavernous malformations are benign vascular lesions composed of abnormal dilated capillaries without intervening brain parenchyma. They can present with seizures (most common, 50–70% of symptomatic cases), focal neurological deficits from microhemorrhages, or headaches. The lesion in this case presents with progressive motor weakness from repeated microhemorrhages in the motor cortex. ### Differential Diagnosis: Non-Enhancing Cortical Lesions | Feature | Cavernoma | Pilocytic Astrocytoma | Hemangioblastoma | DNET | |---------|-----------|----------------------|-------------------|------| | **Enhancement** | None/minimal | Homogeneous, bright | Prominent (mural nodule) | None/minimal | | **Hemosiderin rim** | Pathognomonic | Absent | Absent | Absent | | **Edema** | Minimal | Moderate to severe | Moderate | Minimal | | **Location** | Supratentorial > infratentorial | Cerebellum, brainstem | Cerebellum, spinal cord | Temporal lobe (cortical) | | **Age** | Any age | Pediatric/young adult | Young adult | Pediatric (seizures) | | **Signal on T2** | Mixed (popcorn) | Homogeneous hyperintense | Cystic + solid nodule | Homogeneous hyperintense | **Clinical Pearl:** The hemosiderin rim (hypointense on T2 and gradient-echo sequences) is the imaging hallmark that distinguishes cavernoma from other non-enhancing lesions. This rim represents chronic hemosiderin deposition from repeated microhemorrhages. ### Imaging Algorithm for Non-Enhancing Cortical Lesions ```mermaid flowchart TD A[Non-enhancing Cortical Lesion]:::outcome --> B{Hemosiderin rim present?}:::decision B -->|Yes| C[Cavernous Malformation]:::action B -->|No| D{Location and signal?}:::decision D -->|Temporal lobe + homogeneous| E[DNET]:::outcome D -->|Cerebellum + cystic mural nodule| F[Pilocytic Astrocytoma]:::outcome D -->|Posterior fossa + prominent vessels| G[Hemangioblastoma]:::outcome C --> H[MRI surveillance, seizure prophylaxis]:::action E --> I[Often seizure focus]:::action F --> J[Benign, slow growth]:::action ``` **High-Yield:** Gradient-echo (GRE) or susceptibility-weighted imaging (SWI) sequences are essential for detecting the hemosiderin rim — conventional T1/T2 may underestimate the lesion. The absence of enhancement is crucial: if a lesion enhances, cavernoma becomes less likely. ### Why This Case Fits Cavernoma 1. **No enhancement** — rules out pilocytic astrocytoma and hemangioblastoma (which typically enhance) 2. **Minimal edema** — cavernomas cause less vasogenic edema than tumors 3. **Progressive motor deficit** — consistent with recurrent microhemorrhages in motor cortex 4. **Age and presentation** — cavernomas can present at any age with focal neurological deficits **Mnemonic:** **CHARMS** — Cavernoma Has A Rim of hemosiderin, Minimal enhancement, Seizures (common presentation). [cite:Osborn's Brain Imaging, Pathology, and Anatomy Ch 8; Harrison 21e Ch 375]